2005 PX150 Soft Seize
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Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Thu Sep 05, 2019 4:09 pm quote
Two years ago, I acquired a nearly new US 2005 PX150 (see photo). It had just 368 miles on it. I put on a SIP Road 2 muffler and re-jetted it (102/E1/150 main and a 50/160 slow idle jet). It ran great with a quick throttle response and strong pull throughout the throttle range. After nearly 4000 miles riding this bike, today with the temp at 75 degrees and riding on a level road at about 40 mph, I noticed a pull on the forward motion of the bike. It was like the brakes were being applied. Then after a few seconds, the pull become really bad and the bike was going to come to a screeching stop. I pulled in the clutch and the bike became a free rolling vehicle, the engine was dead. As I coasted to a near stop, I put it in 3rd gear and released the clutch. The engine started and I was able to ride it back home. This appears to have been a soft seize.

What caused this soft seize is unknown. This has never happened before and the bike has been running great for the past 4000 miles. Could my mid-range be too lean? I had installed the 50/160 slow idle jet which is on the lean side. I have in the past tried the richer 55/160 but the bike never ran good with it. The E1 atomizer is also lean but the bike did not run better when I tried the richer BE3. Then again, maybe an air leak occurred making the engine run lean. However, I did re-torque the two carb bolts to 11 ft lbs just 400 miles ago. Regardless, I must now find the cause and fix it. For starters, I will up the jets in the middle range and check the spark plug. As it stands now, my PX150 is not dependable for regular rides in the country.

If anyone has encountered this problem with their 2005 PX150s and has suggestions where I should start testing or jetting I should try, I would be most grateful.

DSC05741.JPG
US 2005 PX150 Vespa.

Addicted
Joined: 26 Jan 2019
Posts: 872
Location: california
Thu Sep 05, 2019 8:04 pm quote
RB - first off - sweet bike.
Frustrating I'm sure to have that happen out of the blue.
I am guessing you might have been lugging it in 4th based on your speed.
That will heat up the motor more than being at higher revs - I was surprised to learn that myself.

Given the circumstances, if it were mine, first thing I would do is check for an air leak as you suspect. Likely culprits include your carb, the head bolts, or internal seals.

Plenty online on how to do a leak down test - but with 20-30 min, you could drop the exhaust pipe down and shove a rubber stopper in the port coming out of the head, pull the carb and carb box and seal off the inlet - small stiff piece of plate aluminum with 1/8" rubber under it is what I use there. Then put about 5 lbs of pressure in through the spark plug and see what happens.

Of course - you could also just check carb bolts, and head bolts, and see if something stands out as outright loose. Wouldn't surprise me to find a head nut not much more than finger tight. Easy enough to check.

Your jet stack seems a bit lean to me - but as you noted - its run fine.
Of course, its possible you were close to the line with that jetting, and an air leak has opened up - together causing the soft seize.

Other's can comment on that front.
If you pull the carb, make sure to have new gaskets.
I like the SIP ones also sold by some of the US shops - they seal nicely for me.
Enthusiast
1965 VBB/2005 Stella
Joined: 16 May 2016
Posts: 77
Location: Leetonia, ohio
Fri Sep 06, 2019 4:32 am quote
I have to agree with Charlieman on the air leak theory. I don't think one would ride 4000 miles on a particular jet stack with no problems then all of sudden experience a soft seize because of the jetting. It don't make sense to me.
An air leak seems much more realistic.
In your opening line you mentioned you acquired this bike in nearly new condition with 368 miles on it.
Meaning it probably had never seen a dealer between when it was produced and today some 14 years later.
Head bolts are the first place I would look since you mentioned the re-torquing of the carb bolts some 400 miles ago but didn't mention the head bolts. Not too sure I would condemn the internal seals with less than 5,000 miles on the bike.
Good luck in your quest in getting to the cause of this. It will be interesting to here your resolve.
I know only to well the feeling of riding a bike with fear of experiencing a soft seize or worse yet a bull blown lockup.
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Thu Sep 12, 2019 2:34 pm quote
Soft Seize Issue Sill Unresolved
Why I had a soft seize riding on a level road at 35 to 45 mph and a 75 degrees ambient temp after 4000 uneventful miles is still unknown. Today, I checked the four head bolts and they were all torqued to specification, none was lose. I checked the spark plug and it looked perhaps a little rich (see photo). I re-torqued the two carb bolts and got just a fraction on both bolts at 11 ft lbs of torque. So I replaced the slow idle jet (50/160) with a richer jet (45/140). I then took the bike on the same route at the same speeds. The ambient temp on this run was 86 degrees. No soft seize occurred and the bike ran great. I still plan to try the richer BE3 mixer and richer 55/160 slow idle jet. For now, the bike is running great and I can find no reason for the soft seize I encountered. The only theory I have for now is the slow idle jet was too lean. But why did it take 4000 miles for it to show up? It is anyone's guess.

DSC06545a.jpg
Iridium spark plug following soft seize.

Addicted
GL, PK, PE200 with hack, Sears Rust Badge
Joined: 24 Apr 2012
Posts: 789
Location: Deep in the heart of Texas
Thu Sep 12, 2019 4:54 pm quote
I can't see down the plug but it does not look too rich from that angle. What did the top of the piston head look like? Did it look like it could be decoked a little or did you see a lot of the metal surface?
Molto Verboso
1980 P125X, 1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 1565
Location: Staten Island, NY
Thu Sep 12, 2019 5:09 pm quote
I think it looks too hot and too rich. White tip over black is hot I believe. It also looks like you might have some metallic speckles on it from being too hot. Check your timing.

Maybe one end of the jetting is too rich and the other is too lean, and your normal riding habits it seems ideal cause they even each other out in the middle and you never push the limit on the extremes enough. And this time you just rode it too hard for too long in the lean throttle range that amplified the incorrect jetting until it seized.
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1670
Location: London UK
Thu Sep 12, 2019 7:36 pm quote
That plug is lean. The grey colour comes after white and means damage is being done. The grey is melted aluminum (piston).

Either an air leak or you have just been lucky until recently. At least now you know and we can fix it.
Ossessionato
Joined: 22 Oct 2011
Posts: 4258
Location: Tega Cay, SC
Fri Sep 13, 2019 3:29 pm quote
Get the 55\160 and Be3 in there. Your midrange is too lean. What 2 stroke oil are you using? Are you premixing or on autolube?

Last edited by Tierney on Sat Sep 14, 2019 7:19 am; edited 1 time in total
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Fri Sep 13, 2019 4:53 pm quote
Based on the great comments received here and the results seen, it is obvious I have been running too lean in the low to mid throttle range. After 4000 miles, it caught up with me.

I am in the process of enriching the low to mid range. The main stack I am now testing is 102/BE5/150 with a slow idle jet of 45/140. The main stack is the same as the original except the main jet is increased to 102 primarily because of the SIP Road 2 muffler installed. The BE5 is richer in the low end compared to the E1 I have been using for the past 4000 miles. The slow idle 45/140 is also slightly richer than the 50/160 that was installed during the 4000 miles. Hopefully, the bike will run as well as it did before with this new jetting. I will report my findings later.

To answer some questions, I use Motul 710 2T fully synthetic oil in the auto lube system that was originally installed in the 2005 PX150.
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1670
Location: London UK
Fri Sep 13, 2019 7:52 pm quote
I think you should find out which main jet you need by testing it. Once you know which one splutters at WOT the correct one won't be much smaller than that.
Enthusiast
GS150, LI200, TX200, PX125, T5200, SX200, PX125 CUTDOWN
Joined: 31 Jul 2019
Posts: 72
Location: South West England
Sun Sep 15, 2019 11:06 am quote
i had the same twice last year, once on a PX with 166 kit and once with my straight sx200.

in both occasions it was 24/25+ degrees out side temp, i was razzing the nuts of them and was using cheaper fully synth. i put it down to my riding in those conditions. Although a mate of mine did say that the barrel can lose mechanical elasticity as they age, so doesn't contract and expand in the same way as the piston does?

in both occasions i did lock up, i rescued the sx but the px sent me tarmac surfing.....

might just be bad luck?
Enthusiast
GS150, LI200, TX200, PX125, T5200, SX200, PX125 CUTDOWN
Joined: 31 Jul 2019
Posts: 72
Location: South West England
Sun Sep 15, 2019 11:10 am quote
Re: Soft Seize Issue Sill Unresolved
RB Prior wrote:
Why I had a soft seize riding on a level road at 35 to 45 mph and a 75 degrees ambient temp after 4000 uneventful miles is still unknown. Today, I checked the four head bolts and they were all torqued to specification, none was lose. I checked the spark plug and it looked perhaps a little rich (see photo). I re-torqued the two carb bolts and got just a fraction on both bolts at 11 ft lbs of torque. So I replaced the slow idle jet (50/160) with a richer jet (45/140). I then took the bike on the same route at the same speeds. The ambient temp on this run was 86 degrees. No soft seize occurred and the bike ran great. I still plan to try the richer BE3 mixer and richer 55/160 slow idle jet. For now, the bike is running great and I can find no reason for the soft seize I encountered. The only theory I have for now is the slow idle jet was too lean. But why did it take 4000 miles for it to show up? It is anyone's guess.
looks lean to me mate.....
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Mon Sep 16, 2019 6:53 pm quote
Jack221 wrote:
That plug is lean. The grey colour comes after white and means damage is being done. The grey is melted aluminum (piston).

Either an air leak or you have just been lucky until recently. At least now you know and we can fix it.
Wow, does the aluminum actually melt? The melting point for aluminum is 1221 degrees F. I did not know these engines could get that hot during a soft seize.
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1670
Location: London UK
Mon Sep 16, 2019 8:10 pm quote
Well that's a coincidence. About the same temperature that the spark plug tip normally runs at. On a lean running engine, which is running hot enough to soft seize, the plug tip will be about 400 degrees hotter (1600F). Add the extra pressure from the detonation that will be occurring in the squish area and the aluminum doesn't stand a chance.


However, unlikely you have done any major damage. Just get it jetted correctly and will run for many years.

dsc06545a_18427.jpg
Tip melted? Iridium plug should handle 1800F

Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Tue Sep 17, 2019 1:03 pm quote
Jet Testing Update
To review, my previous jetting was 102/E1/150 main stack and 50/160 slow idle. The 2005 PX150 ran great with this combo but I experienced a soft seize at about 4000 miles. My riding style is in the lower to mid throttle range and the leanness of this combo in this range led to the soft seize. So my intent was to enrich the low to mid throttle range to prevent any further soft seizes.

I tried various combinations of jets in the main stack and ended up with two that performed the best. These were:

101/BE3/150 and 102/BE5/160

Both stacks worked well but I had a “feeling” the BE5 performed the best. I also increased the main air from 150 to 160 to lean out the main stack slightly. The 102/BE5/160 stack is richer than the 102/E1/150 and 101/BE3/150 since the BE5 is richer than the E1 and BE3 especially in the lower end. The holes below the collar are smaller on the BE5 compared to the E1 and BE3 (blue arrow in photo) and thus it is richer in the lower end.

I tried several slow idle jets and ended up with the richer 55/160. Compared to the 50/160 I was using at the time of the soft seize, the 55/160 slow idle jet is significantly richer.

So the jetting I am currently testing is comprised of a 102/BE5/160 main stack and a 55/160 slow idle jet. Hopefully, the low to mid range has been enriched and I will not encounter a soft seize in this range again. Currently, the bike is running great, it idles nicely, responds quickly to the throttle, shows no four stroking while cruising at 35 to 40 mph, and has lots of torque and pull through the throttle range. I will check the spark plug later when I have more miles on it.

My thanks to all who helped me with this problem.

DSC06109.aJPG.JPG
Comparison of various mixer tubes.

Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Wed Sep 18, 2019 1:03 pm quote
Jetting Update
I made some minor changes to the jetting I previously reported. I replaced the 160 air with a 150 to enrich slightly the main stack. The current main stack is as follows:

102/BE5/150

With the exception of the 102 main jet, this is the standard stack that Piaggio used in this bike.

I also replaced the slow idle 55/160 with a slightly leaner 45/140. This slow idle jet is still richer than the 50/160 I was using at the time of the soft seize. The addition of the BE5 mixer and 45/140 slow idle should enrich the lower end where I ride the most.

Regarding the slow idle jet, it is interesting to note that the stock 2005 PX150 came with a 45/160. This 45/160 is an extremely lean jet and leaner than the 50/160 I was using at the time of the soft seize. Surely Piaggio knew that most of the customers would ride in the low to mid throttle range. I would speculate that the extremely lean slow idle jet was used to comply with the EPA emission standards. Maybe the catalyzed stock muffler helped prevent soft seizes in the low end. I really don't know.
Ossessionato
1964 GS 160 MK II, 1967 Vespa GT, 1968 SS180, 1964 Vespa GL, 1964 Vespa VBB, 2006 Buddy 125, 2013 BMW C650GT
Joined: 07 Apr 2008
Posts: 2951
Location: Boca Raton, Florida
Thu Sep 19, 2019 6:14 am quote
RB Prior wrote:
Jack221 wrote:
That plug is lean. The grey colour comes after white and means damage is being done. The grey is melted aluminum (piston).

Either an air leak or you have just been lucky until recently. At least now you know and we can fix it.
Wow, does the aluminum actually melt? The melting point for aluminum is 1221 degrees F. I did not know these engines could get that hot during a soft seize.
That is why an EGT gauge can be very useful. It lets you know what is happening now while the CHT lets you know more of what has happened already.
bodgemaster
1963 GL, 1976 Super (x 2), 1974 Primavera (x 2), 2006 Fly 150
Joined: 26 Sep 2013
Posts: 5041
Location: So Cal
Thu Sep 19, 2019 7:30 am quote
Any recommendations for a good EGT gauge?
Ossessionato
2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
Joined: 26 May 2013
Posts: 3900
Location: That bushfire place
Sat Sep 21, 2019 4:42 am quote
For starters... fit a BIGGER main jet!
Ossessionato
2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
Joined: 26 May 2013
Posts: 3900
Location: That bushfire place
Sat Sep 21, 2019 5:01 am quote
A wee bit on mixers & how come the pic shows leaner->Richer
... the BIGGER the holes, the MORE AIR get mixed into the fuel.
The further UP the mixer, the HIGHER he REVS it relates too...

So (in theory);
BE2 would be good if you want to use a big-arse main jet, so down low/mid-range it adds a heap of air to lean it out...
When going full throttle theres not a lot of difference in these options.
Ive used a toothpick jammed in a top hole, then snapped to block one or more of the holes for full throttle to richen up the mix a bit (rather than fitting an even bigger main jet).... it's cheap and simple and worth a try.
NOTE; reasons for using the tapered end of a wooden toothpick is that it jams nicely into the wee holes, easy to cleanly snap off, easy/quick to add/remove, if they do fall out while testing it causes no damage to engine as nice n soft material, won't damage the holes/mixer


Crap... i knew i read it somewhere before...

Four-Stroking

90AF7F1C-4161-4811-8F4C-6A049123793A.jpeg

Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Sat Sep 21, 2019 9:56 am quote
Slow Idle Jets
I am satisfied with the main stack I am currently using. It is a 102/BE5/150. This is the stock stack that came with the 2005 PX150 except I increased the 98 main to 102 when I installed the SIP Road 2 muffler.

Now I am evaluating various slow idle jets. My initial problem was a soft seize while riding in the low to mid throttle range. So I tried to enrich this lower end with the slow idle jet. Below is a chart showing various slow idle jets. Their richness and relationship to the main are shown. The jet in red was the one I was using at the time of the soft seize. It was too lean in my riding style. Note that the stock jet that came with the bike in green is the leanest one shown. The three jets I am evaluating are in blue. The 55/160 is richer but my bike just does not run as well with it. The 45/140 works well and is richer than the jet (50/160) I was using when the soft seize occurred. I just received a new slow idle jet (40/120) that is between the 55/160 and 45/140 in richness. I am currently evaluating this jet. It does have less of an overlap with the main. Whether I like this remains to be seen. Regardless of which jet (in blue) I end up using, I am sure my low to mid range has been enriched and another soft seize would be remote.

screen_shot_2011_02_15_at_095130__187 4.jpg
Slow Idle Jet Chart.

Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Sat Sep 21, 2019 3:37 pm quote
Air Filter: To Drill or Not To Drill
Another variable that affects the fuel mixture in both the main stack and slow idle jet is the air filter. My stock 2005 PX150 came with a standard air filter without holes above the jet stacks. I ordered an air filter with the two holes already drilled at the factory and installed it shortly after I got the bike (see photo). After thinking about this, I have concluded that these two holes (blue arrows) lean out the jets by allowing more air to enter the jet stacks. As to how much I do not know. The original design did not have these holes but just a barrier (red arrow) where the air has to pass over in order to access the jets. Without these two holes, I would suspect the jets to run richer. Using an air filter with these two holes may have been a contributor to my soft seize described in this thread.

Perhaps someone can better explain whether drilling these two holes is good. I think the holes are suppose to improve throttle response and performance. But, if it is at the expense of running leaner than normal, then is it a good idea? Comments on using an air filter with these two holes in a rather stock PX150, jetted for the SIP Road 2 muffler, are most welcome.

DSC06583a.jpg
Piaggio air cleaner with two holes drilled (blue arrows) and standard barrier (red arrow). This air filter was made at the factory.

Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Tue Sep 24, 2019 7:47 am quote
Final Jettting
Jetting is an art as much as it is a science. Every engine is different. In my case with the PX150, I had a soft seize while cruising at around 35 to 40 mph which is my riding style. That was an indicator that I was too lean in the low to mid throttle range. After much testing, here is what I now have installed regarding the jets.

My main stack is 102/BE5/150. This definitely enriched the low to mid throttle range primarily because of the BE5 mixer. As for the slow idle jet, I tried the richer 55/160 and it "felt" a little too rich for my bike. I also tried the 45/140 which is leaner. The bike ran well but I was still concerned it may be too lean for my riding style. So I got a slow idle jet that was in between these two, the 40/120. It has a ratio of 3.00 and falls right in between the 55/160 and 45/140 (see chart below). While this jet has less of an overlap with the main, it works great. The bike idles smoothly, responds to the throttle instantly, there is no four stroking while cruising around 35 to 40 mph, and the bike is strong and smooth through the all gears up to 50 mph and above. Overall, it is a good fit for this bike and I am most pleased. I think I have enriched my low to mid throttle range enough to prevent a further soft seize and still maintain the superb performance of this 2005 PX150. I will continue to evaluate this jetting combo and check the spark plug after I put some miles on it. But for now, the bike could not run better.

Note: The bike is a US 2005 PX150 that is stock except for the SIP Road 2 muffler that was installed. The drilled air filter was also installed. The idle mixture screw was turned CCW one half turn from the stock position. I also replaced the iridium spark plug I was using with a standard NGK BR7HS spark plug. Motul 710 Synthetic oil is used in the auto lub system.

screen_shot_2011_02_15_at_095130__187 6.jpg
Slow idle jet chart showing the optimal jet (circled) currently in use. For a description of the various colors, see my previous posting.

bodgemaster
1963 GL, 1976 Super (x 2), 1974 Primavera (x 2), 2006 Fly 150
Joined: 26 Sep 2013
Posts: 5041
Location: So Cal
Tue Sep 24, 2019 8:42 am quote
I wouldn’t get too hung up on the ratio. I think your first concern should be to select an idle jet that flows sufficient fuel. You’re more likely to seize running the “richer” 45/120 than with the “leaner” 55/160.
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Tue Sep 24, 2019 1:18 pm quote
SoCalGuy wrote:
I wouldn’t get too hung up on the ratio. I think your first concern should be to select an idle jet that flows sufficient fuel. You’re more likely to seize running the “richer” 45/120 than with the “leaner” 55/160.
Thank you SoCalGuy for your comments. If I understand you correctly, you are implying that given a certain engine running at a certain rpm, the leaner 55/160 slow idle jet will allow more fuel to pass than the richer 45/120. This shoots down those charts showing the ratios of the slow idle jet (air diameter divided by fuel orifice diameter) where the lower number is richer than the higher number. Perhaps these jets should be tested for the amount of fuel to pass through per specified time at a standard pressure. So how do I select an idle jet that flows sufficient fuel as you suggest?. Other than using the ratios in the charts, I don't know. What I do know is that my bike runs better with the slightly leaner 40/120 than with the richer 55/160 slow idle jet. It did soft seize with the much leaner 50/160. Whether my PX150 will soft seize later with my current set up using the 40/120 slow idle jet remains to be seen. I am betting it will not.
bodgemaster
1963 GL, 1976 Super (x 2), 1974 Primavera (x 2), 2006 Fly 150
Joined: 26 Sep 2013
Posts: 5041
Location: So Cal
Tue Sep 24, 2019 3:14 pm quote
Quote:
So how do I select an idle jet that flows sufficient fuel as you suggest?
On a stock bike start with at least the same size fuel opening as the one that came from the factory. Anything smaller is asking for trouble.
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Tue Sep 24, 2019 8:37 pm quote
SoCalGuy wrote:
Quote:
So how do I select an idle jet that flows sufficient fuel as you suggest?
On a stock bike start with at least the same size fuel opening as the one that came from the factory. Anything smaller is asking for trouble.
The stock slow idle jet that came with my 2005 PX150 was a 45/160, the leanest jet shown in the chart below (green). All the jets I have tried and evaluated were richer than the stock jet. These include the 50/160 (red), the jet I was using at the time of the soft seize. The others (blue) were richer than the 50/160 and I found the best one overall to be the 40/120 (circled). The fuel opening of the 40/120 is smaller than the stock jet but overall, it is a much richer jet. Finding the right jetting may seem like a crap shoot but I relied on these charts and the "feel" of the bike during the evaluations.

I respect and appreciate SoCalGuy's comments. I hope I am not asking for trouble since the 40 fuel opening of the 40/120 is certainly smaller than the 45 in the stock 45/160. But the air opening seems to play a big part in determining the amount of fuel in the mixture as well. The 120 air in the 40/120 does show a richer jet overall compared to the 160 in the stock 45/160 in the chart. I would have preferred to use the 55/160 but it seemed to diminish the performance of my bike slightly. The 45/140 worked very well but I wanted a slightly richer jet for insurance (40/120). The bottom line is selecting a jet that will allow more fuel into the engine while maintaining performance and thereby reducing the chances of another seize in the low to mid throttle range. I guess only time will tell if I succeeded.

screen_shot_2011_02_15_at_095130__187 6.jpg
Slow idle jet chart showing the various jets evaluated (in color).

Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Thu Sep 26, 2019 3:55 pm quote
Jetting Con't
SoCalGuy wrote:
I wouldn’t get too hung up on the ratio. I think your first concern should be to select an idle jet that flows sufficient fuel. You’re more likely to seize running the “richer” 45/120 than with the “leaner” 55/160.
I have been thinking about what SoCalGuy said regarding the fuel opening in the slow idle jet and I believe his is on to something. I ordered another slow idle jet that is nearly identical to the 55/160. I added this new jet to the chart below. This jet is a 48/140 and has a ratio nearly the same as the 55/160. However, based on SoCalGuy comments, it may be "leaner" than the 55/160 even though the ratios are nearly the same. Given a certain engine drawing in a certain amount of air to mix with the fuel, it stands to reason the smaller fuel opening would be "leaner" than one with a larger fuel opening like the 55/160. Based on just ratios, a hypothetical 35/100 jet with a ratio of 2.86 should be richer than the 55/160 (2.91 ratio). But the 55/160 should allow more fuel to flow into the engine since its fuel opening is much larger and thus it would be "richer". So while I am waiting for the 48/140 jet, I re-installed the 55/160 jet in my PX150. The bike smokes a little on startup when cold but overall the bike runs great. I like this extra insurance of the 55/160 and will use it for now. Based on my riding style in the low to mid throttle range, I feel it will work fine and reduce the chances of a soft seize. Whether I try the new 48/140 is questionable. If the 55/160 keeps working as it is and the plug looks good, I will leave it alone.

To summarize:
Main jet stack is 102/BE5/150
Slow idle jet is 55/160

The bike is a stock US 2005 PX150 with a SIP Road 2 muffler and drilled air filter.

My thanks to all those who contributed to this thread with such great comments and suggestions.

screen_shot_2011_02_15_at_095130__187 7.jpg
Slow idle jet chart with 48/140 added (in bold face).

Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1670
Location: London UK
Thu Sep 26, 2019 6:48 pm quote
Like how you are trying with this. I think your 40/120 was probably not a bad choice. You know emulsion jet fuel delivery is a curve and not just any old regular curve.
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Sat Sep 28, 2019 7:05 am quote
Carabuetator Tuning
The Stella service manual describes how to tune the carburetor. Since the Stella engine is nearly identical to the PX150, I thought some information might be applicable to my PX150. In the section on carburetor tuning, they show a fig 61 but a description of this figure is not shown. Could anyone tell me what this figure 61 (shown below) is suppose to show? What do the various rings represent and what is shown in the center. Do the "open" markings represent the throttle position? I have tried to figure this out but have not be successful. Thanks.

BTW, the stock Stella came with the following jets:

Main jet stack 92/E3/140
Slow idle jet 40/130 (ratio 3.250)

This jetting is rather lean in the main stack although the slow idle jet is richer that the stock PX150 (45/160 ratio 3.556). Would the reed valve on the Stella have any effect on the use of this jet combo? Just curious.

Stella Service Manual Carb Tuning.jpg
Fig 61 from the Stella service manual.

Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Mon Sep 30, 2019 4:05 pm quote
Auto Lub Question
After checking various sources, I find that the slow idle jets that came stock with my US 2005 PX150 and the early Stellas were leaner than the slow idle jet I was using at time of the soft seize. I think now that perhaps my jetting was sufficiently rich enough for my setup and riding style. So why the soft seize while riding at around 1/4 throttle on a level road?

One aspect I have not looked into is the auto lub system. It was designed to ensure the correct lubrication at various speeds and load conditions. Thus, the quantity of oil sucked into the engine changes according to the throttle opening and engine rpm. What if not enough oil was being supplied during my ride at 1/4 throttle? Perhaps there was a head wind and the engine was laboring to maintain my cruising speed. Even though adequate fuel was being supplied, perhaps not enough 2 stroke oil was getting into the engine. If that is the case, short of using 2% premix and not the auto lub system, is there a way to enrich the auto lub system at the lower rpm range? I would guess there is not but perhaps someone has done it.
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1247
Location: UK (South East)
Tue Oct 01, 2019 3:09 am quote
There are plenty of setups using 166, 177 and 187cc and autolube, not to mention the many large block (2xx) setups, but they have slightly different metering by using a different pump cog. Granted they usually have 24mm carbs, but I cannot see that oil metering is your issue, unless the autolube is defective.

When one of my PX150 scoots (2005) was still stock, I added a SIP Road and upped the main to 102, but kept the rest of the jetting as per the factory. It was so slow that I didn't keep it as a 150 for long, but it ran very well. It was a Euro 2 spec with the cat exhaust, so jetting may have differed from your US spec. In those days Piaggio had already started the emissions reduction (choking the P series), so scoots were jetted leaner from the factory. Most people just revert to the jetting of the old PX150e and increase the main when they add a sports pipe and/or drilled filter. For you that would be:

Idle: 55/160
Main: 160/BE3/100-102
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Tue Oct 01, 2019 12:02 pm quote
swa45 wrote:
Most people just revert to the jetting of the old PX150e and increase the main when they add a sports pipe and/or drilled filter. For you that would be:

Idle: 55/160
Main: 160/BE3/100-102
Thank you SWA45 for your comments. I am currently using the following setup in my US 2005 PX150 with SIP Road 2 muffler and drilled air filter and the bike is running great:

Idle: 55/160
Main: 150/BE5/102

I feel the 150 air makes the main stack slightly richer and the use of the BE5 mixer enriches the low to mid throttle range where I usually ride.

As for the auto lub, there are certain aspects that intrigue me. For example, at a given rpm and throttle setting, the auto lub will allow a certain amount of 2T oil to be sucked into the engine. During this process, the fuel is mixed with the oil resulting in a certain fuel/oil mixture. In pre-mix setups, this is set at 2%. So if the jetting is lean, the fuel/oil ratio would be higher than if the jetting were richer. When it comes to a soft seize, is this a result of 2T oil insufficiency or the insufficiency of the fuel/oil mixture in general? If it is the latter, then enriching the jets as I have done would be very beneficial regardless of the resulting fuel/oil ratio. Needless to say, this is a very simplistic overview of the auto lub system and its relationship to the jets. In the end, for a specific engine, there is an optimum setup that will allow the bike to perform at its best and also prevent soft seizes from occurring. I hope I am getting close.
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Thu Oct 03, 2019 9:00 pm quote
I received a 48/140 slow idle jet today to evaluate. It was rather hard to find and I finally got one from Racing Planet USA in Flordia. The 48/140 jet is very similar to the 55/160 when comparing fuel/air rations (2.917 vs 2.909, respectively). Its relationship to the other jets I have tried is show in the chart. I tried a 45/120 and it was much too rich. The stock 45/160 was too lean and the 50/160 was the jet I was using at the time of the soft seize. Both the 45/140 and 40/120 worked well but I was concerned they may be a bit too lean for my lower third throttle riding style.

Both the 48/140 and 55/160 perform well in my US 2005 PX150. I will leave the 48/140 in my bike for the remainder of the riding season. There is a subtle difference between the two and I seem to prefer the 48/140. Perhaps it is the lesser overlap with the main. I don't really know. My main jet stack remains 102/BE5/150. I will check the plug later and post photos here.

screen_shot_2011_02_15_at_095130__187 7.jpg
Slow idle jet chart showing the relationship of the 48/140 (in bold) with the other jets.

Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1247
Location: UK (South East)
Thu Oct 03, 2019 11:32 pm quote
My other PX150 (2012 model), had a 45/140 and 140/BE5/98 as the stock jetting. This was Euro 3 with the latest (and most restricted) cat exhaust with the secondary air thingy, and with the RPM restricted ignition. When I ran a DR177 top end until recently, I kept the 45/140 and the restricted ignition, despite changing the exhaust to a SIP Road. I experimented with the stock 140/BE5 and 160/BE3 stacks and was happy with both, although I ended up keeping the 160/BE3 for some reason (laziness probably). It ran really well and the cylinder and piston were like new when I removed the kit. You should be fine with the 48/140 and most likely the 45/140.
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Fri Oct 04, 2019 12:59 pm quote
Here are two plug photos after 20 miles with the following setup:

Main Jet Stack: 102/BE5/150
Slow Idle Jet: 48/140

US 2005 PX150, air filter drilled, SIP Road 2 muffler.

More miles on this setup are needed to get better plug results. However, with the limited miles, the plug does not look too lean nor too rich.

DSC06587.JPG
Spark plug following 20 miles with the 48/140 slow idle jet.

DSC06594.JPG
Spark plug following 20 miles with the 48/140 slow idle jet.

Addicted
GL, PK, PE200 with hack, Sears Rust Badge
Joined: 24 Apr 2012
Posts: 789
Location: Deep in the heart of Texas
Fri Oct 04, 2019 1:20 pm quote
Still lean. Cut the threads off and you'll see mostly white but plug tip is black because it's running hot.
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Fri Oct 04, 2019 3:24 pm quote
rowdyc wrote:
Still lean. Cut the threads off and you'll see mostly white but plug tip is black because it's running hot.
So what is your recommendation to fix this lean condition? Do I enrich the jetting more, perhaps a larger main Do I go to a cooler plug? Should I run a premix of say !% to supplement the auto lub? Assuming the timing is correct as it has never been changed from the stock setting, where do I go now? I certainly do not what another soft seize. The bike is currently running great. Thanks.
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 300
Location: Central Ohio
Sat Oct 05, 2019 2:30 pm quote
Today I tried the following jetting in my US 2005 PX150 with SIP Road 2 muffler and air filter drilled:

Main stack: 102/BE3/160
Slow idle jet: 55/160

The plug after 20 miles is shown below. The bike runs great and I feel is running overall richer than before. I know I have said this before but I think I will leave it alone for now and enjoy riding it. I feel getting another soft seize with this setup is very remote.

Also shown below is a simplistic diagram of the SI carburetor. The fuel (red) and air (blue) paths through the jets I colored in. Interestingly, the slow idle jet gets its fuel from the main stack with is determined by the main jet. I am for now ignoring the idle mixture screw but it is connected to the slow idle jet as well. I went with the BE3 mixer even though it is leaner than the BE5 in the low throttle range. I think the richer 55/160 jet compensates for this. Lastly, someone once said that the two air correctors should be the same size if possible. I know this does not occur in many cases but in my current set up, they are both 160.

DSC06604.JPG
Spark plug after 20 miles with the 102/BE3/160 main stack and 55/160 slow idle jet.

SI Carb Diagram 2.jpg
Simplistic diagram of SI carburetor showing fuel (red) and air (blue) flow through the jets.

Enthusiast
PX150E
Joined: 28 Oct 2018
Posts: 68
Location: Florida, USA
Sun Oct 06, 2019 4:10 am quote
RB Prior,
I have been following your thread closely to see what I could learn from your experience. My PX 150E is not from the same year as yours, but a 1985, all original US specs, bought new 34 years ago.
My stock factory setting was: 42/140 slow jet and 100/BE5/150 on the original Dellorto 20/20. Stock muffler, undrilled air filter. Performance was OK, but it had a big flat spot in the range.

After a complete engine rebuild with a new SPACO 20/20 carb, last year, I was having a hell of a time to make it run properly. The jetting on the new SPACO (bought new from SIP) was: 48/160 and 100/BE/160. The bogging just off-idle was maddening, and the scooter was almost unrideable.

I then installed the original jetting from the old carb (warped after 30+ years) into the new SPACO carb; better, but not by much.
It just did not like the original 42/140 jet, no matter how many turns the mixture screw was set at.
The 48/160 with 100BE3/160 combo and mix screw at 1.5 turns out proved to be a big improvement, but what improved things even more was the change to 100BE5/150 with same mix screw setting. I then drilled and installed a new air filter, and the change was dramatically better. No more flat spots, much smoother acceleration, and the best overall performance it ever had. The only thing that has worsened is the fuel consumption, which went from 85 mpg to about 70 mpg. Plug looks light-brown good, and no bogging.

A couple of things that remain a mystery to me even after asking on this forum: My plug has always been the long reach (BP6ES or ND W20ES) not the short HS called for even in the manual; second, what does that metal tag on the carb top with R-585 or R-590 mean? My original carb had no tags, and I suspect it has to do with other aspects of the carb set up that no one can comment on.

Anyway, after 40,000 miles and 34 years, this scooter has been a hoot to ride and own....and I am sure you feel the same with yours, now that you have the jetting sorted.
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