2005 PX150 Soft Seize
Post Reply    Forum -> Not-So-Modern
Author Message
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 242
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: 591
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: 71
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: 242
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
Joined: 24 Apr 2012
Posts: 661
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?
Addicted
1980 P200E project, 2005 Stella Malossi 166 MKIII
Joined: 20 Jul 2018
Posts: 968
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: 1419
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: 3907
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: 242
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: 1419
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: 63
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: 63
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: 242
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: 1419
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: 242
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: 242
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: 2918
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.
Ossessionato
1976 Super (x 2), 1974 Primavera (x 2), 2006 Fly 150
Joined: 26 Sep 2013
Posts: 4822
Location: So Cal
Thu Sep 19, 2019 7:30 am quote
Any recommendations for a good EGT gauge?
Scooting the Ozarks is a scooter rally held in Eureka Springs, Arkansas offering riders scenic twisty rides, poker run, and more.   vespa scooterwest scooter west Motorsport Scooters   Cool Ass scooter seat cover
Post Reply    Forum -> Not-So-Modern
[ Time: 0.8296s ][ Queries: 28 (0.0841s) ][ Debug on ]