Fuel Starvation or soft seize advice? SOLUTION Main too rich
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Hooked
Joined: 26 Jan 2019
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Fri Mar 29, 2019 10:38 am quote
Great explanation - now makes full sense.
Your assumption at the end is insightful - could it be the idle jet affecting the start/choke you mention vs main?

Clearly you are getting a lot more pull in the upper 1/3 of the rev range than you had.

Funny - mine as well - first kick - choke spring little too tight/strong so it wont stay out on its own - but bike doesn't need it - pretty much goes straight to idel at 55 degree outdoor temps (hey - I am in Cali - that's our version of cold).

Also experiencing what sounds like similar tuning needs - nice pull (even with my side car weighing it down) off the line - remarkably torky - but just no guts above the 2/3 RPM level.

Suspect my main is too rich based on your posts and Jack's tuning input. Due to run the plug test - but working on making the bike more sound over all before focusing there.

Thanks!
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Fri Mar 29, 2019 2:18 pm quote
Jack221 has definitely been an immense help, greatly appreciated! His info about how plugs are supposed to look and the associated jetting changes, along with fmp videos and some other sources on YouTube are invaluable to people like us just getting started but really trying to get hands dirty understanding how everything on these machines works.

I'm definitely enjoying the process of learning and working on them. It's rewarding. Hopefully you can get your bike carb set a little better for some cleaner running. I'm sure the added weight of the side car probably doesn't help either!

If you haven't yet, I'd suggest watching some videos from thatscooterthing on YouTube. Very informative and straightforward videos on rebuilding engines, and he is responsive to questions and willing to help out with advice on his live streams.
https://m.youtube.com/thatscooterthing
Molto Verboso
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Fri Mar 29, 2019 7:25 pm quote
A correctly set up carb makes all the difference but getting there can be a challenge.
Knowing what is rich or lean is most of the battle. This is where the choke test comes in. Sometimes its really hard to tell. Every throttle position needs to be set up by making rich or lean decisions. It's not always obvious which either. They both sound so similar. The plug helps a lot. As does a temperature gauge and a good ear. Vibration is another way (weak vibrates btw). 2 strokes are so complicated.
Hooked
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Sat Mar 30, 2019 7:21 am quote
Quote:
I'd suggest watching some videos from thatscooterthing on YouTube.
Thanks Swiss - will browse through some of his - looks like he has a lota good stuff.
Quote:
The plug helps a lot.
Tks Jack. Question: Im starting with a 99% stock 150 VBB - rebuilt to spec. It has a 12 volt ignition - but still uses points.

What plug would you start with to do initial testing?
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Sat Mar 30, 2019 9:16 am quote
Regarding my idle jet, i only had an hour before work today, so i didn't swap jet out but i warmed engine up with a ride then adjusted the air mix screw for first time since bringing the really rich main jet down to 100. The current idle jet, 45/140, is set correctly at 1.25 full turns out. I have both sizes leaner, 38/120 and 40/130. The correct idle jet defined by manufacturer is 40/130, which is two sizes leaner than where i am currently at. My first day off Monday i will change this out back to the normal 40/130 suggested by genuine and make adjustments, check plug again. Hopefully that is good and not too lean, because I'm loving the drastic increase in fuel economy I've gained just from bringing the main down to normal. I'm really curious to see the acceleration changes with a two step leaner idle jet, given the drastic changes from the main jet.

When i was at 45/140 idle, 140/be1/116 main, my fuel economy was about 40mpg. Currently same idle jet with main down to 100 i am at 60mpg with two full tanks at that jetting to confirm it. 70-80mpg would be amazing but I'll be happy with any increase especially with prices steadily increasing the last two weeks and nearing $3/gal again in nyc.
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Sat Mar 30, 2019 9:23 am quote
charlieman22 wrote:
Quote:
I'd suggest watching some videos from thatscooterthing on YouTube.
Thanks Swiss - will browse through some of his - looks like he has a lota good stuff.
Quote:
The plug helps a lot.
Tks Jack. Question: Im starting with a 99% stock 150 VBB - rebuilt to spec. It has a 12 volt ignition - but still uses points.

What plug would you start with to do initial testing?
Jack would know better whether this is correct temp plug, but in meantime a quick search on scooter mercato gave this b7 plug for vintage/vbb. Looks like it has shorter threads compared to my Stella and later px engines.

http://www.scootermercato.com/Scooter-Parts/Spark-Plugs/2-B7HS
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Sun Mar 31, 2019 9:10 am quote
Spark plug
And yet again Jack saves my Bacon. I normally run with a B7HS all the time. Thought Id change it for a B6HS as it looked like the cold one in the pictures. Went for a run and thought Id better check the Idle mixture using his method. It was running weak. Cheers Jack I get to ride another day.
Molto Verboso
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Sun Mar 31, 2019 7:17 pm quote
charlieman22 wrote:
Quote:
I'd suggest watching some videos from thatscooterthing on YouTube.
Thanks Swiss - will browse through some of his - looks like he has a lota good stuff.
Quote:
The plug helps a lot.
Tks Jack. Question: Im starting with a 99% stock 150 VBB - rebuilt to spec. It has a 12 volt ignition - but still uses points.

What plug would you start with to do initial testing?
Even if your VBB has been converted to 3 port (which is unlikely), it still won't make enough heat to need more than a B6 plug.
Once you have got used to riding it and not it riding you, there will come a time when it needs a bit more torque. Things can be done. When you're ready.
Molto Verboso
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Sun Mar 31, 2019 7:27 pm quote
Re: Spark plug
worrywort wrote:
And yet again Jack saves my Bacon. I normally run with a B7HS all the time. Thought Id change it for a B6HS as it looked like the cold one in the pictures. Went for a run and thought Id better check the Idle mixture using his method. It was running weak. Cheers Jack I get to ride another day.
Would imagine it rides a little better too. I have my uses.
Many guys do the same. No one ever bothers to look at the plug and see if they actually need a higher number.....or not (And its usually not).
Can keep the B7 for a spare, will still get you home.
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Mon Apr 08, 2019 8:52 am quote
Here are my plug checks after dropping the idle jet down two sizes to stock for stella. I think the main can come down to 99.


The idle jet plug check confuses me as there is a glob of wet oil/gas on the plug, but the plug itself is reddish brown looks good. I'm thinking the wet spot in the idle plug check is from unburned fuel after shutting the bike down, and that the air mix setting is correct. If not that, then I need to turn it in slightly, but that confuses me as I'm already slightly under 2 full turns at about 1.75 turns out from closed. I read many places that say under 2 full turns and you are too rich on the idle jet, but this is the stock idle jet for the stella.

IMG_20190408_115749.jpg
130/40 idle jet. 100 main. WOT 2nd gear 15 seconds +.

IMG_20190408_123847.jpg
130/40 idle jet. 100 main. 1/4 throttle for 5-10 sec before shutting down. wet spot a sign of too rich air mix or just unburned fuel?

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Mon Apr 08, 2019 8:57 am quote
The sensor ring on the plug looks like it may be getting to the end of its useful life
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Mon Apr 08, 2019 9:06 am quote
SoCalGuy wrote:
The sensor ring on the plug looks like it may be getting to the end of its useful life
Oh it is! I've bent it back into shape enough times and i'll keep doing it until it breaks! Temp readings are still good. Its basically brand new only 3 months old but its been chewed up from putting plug on and off so many times to get this jetting correct. The temp gauge came with 3 rings so I'm trying to save the spares until I'm done jetting the stock engine and then with the malossi 166 I put on in the next 2 months.
Molto Verboso
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Mon Apr 08, 2019 7:19 pm quote
I don't like the look of that wet blob. Probably picked up as the plug came out but looks more like gear oil than 2 stroke oil.......

Plug is looking dark for that jetting. How's the gearbox oil look?
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Mon Apr 08, 2019 8:06 pm quote
Jack221 wrote:
I don't like the look of that wet blob. Probably picked up as the plug came out but looks more like gear oil than 2 stroke oil.......
I'll have to drain the gearbox oil and check. I think it came from pulling plug out as the plug base that seats up against the cylinder head and the temp sensor ring had wet oil on it when i pulled it out.

Last edited by swiss1939 on Mon Apr 08, 2019 9:48 pm; edited 1 time in total
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Mon Apr 08, 2019 9:25 pm quote
Jack221 wrote:
Plug is looking dark for that jetting. How's the gearbox oil look?
That first picture of the most recent wot plug check might also be a bit dark because i pulled choke out to test if it would bog down in the middle of the run. I did hold full throttle for about 10 seconds after putting the choke back off, but the plug probably didn't burn off all the extra fuel/oil in that time, so it's not an entirely accurate view of that main jet.
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Mon Apr 22, 2019 4:40 pm quote
Hey Jack221, or anyone for that matter, I'm confused with another issue at 1/4 throttle when warmed up and am trying to debug it. Assuming it's air mix screw setting but can't decide if it's too lean or too rich. I read somewhere either on here or elsewhere that my symptoms mean a lean idle jet/air mix, so i just enriched the idle by opening the air mix screw maybe a half a turn or so and it still seems to be there.

Symptoms are when it's warmed up, if i back off throttle for a few seconds then hit the throttle it hesitates a second where i can feel like it's building up energy but being held back then a split second later it bursts through the imaginary wall and surges forward. So I'll go riding down an empty street and just keep playing with it too see where it is and it's always at quarter throttle with varying degrees of hesitation. I'll hold quarter throttle as long as i can and it doesn't hesitate it runs fine, maybe even sounds too rich as it sounds like it's four stroking to me. If i start from stopped and accelerate consistently up from zero throughout the gears there is no hesitation and it feels pulling strong with no four stroking or dead spots. Only happens when i am at higher revs and back off slightly to the point where I'm at the lower quarter of throttle then hit throttle again. I'm probably over analyzing this stuff but just trying to understand what that issue is from.

Two photos of same plug just slightly different lighting. Plug is from holding quarter throttle for 10 seconds. All of my jetting is exactly the same as last update, just opened up the air mix screw half a turn.

IMG_20190422_202504.jpg
Flash on camera made the tip lighter that in person

IMG_20190422_202543.jpg
No flash and it is a bit darker. Actual color in-between both of these photos



Last edited by swiss1939 on Mon Apr 22, 2019 5:35 pm; edited 2 times in total
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Mon Apr 22, 2019 5:22 pm quote
The reason I am confused about whether it is rich or lean is because, if as it was suggested wherever I read it that this is a symptom of lean idle, then why is there four stroking when I hold 1/4 throttle, and the plug seems a bit rich now? Conversely, if it is too rich, I am at 1.875 turns out on the air screw. General consensus I have read online is that less than 2 full turns on the air mix = too rich idle jet. I am at the stock idle jet for this bike, and I don't have a stock pipe on the bike, so how could this idle jet be too rich? I would imagine going to performance pipe would affect the stock idle jet to be too lean at stock air mix turns, hence I would not be below 2 full turns, but need to go over two full turns, not further below two full turns than I already am with the air mix screw.

I just dont know...

Then again, I am not at stock atomizer.. currently using a be1 instead of be3. So that probably plays into the air mix screw setttings away from stock to begin with.
Molto Verboso
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Mon Apr 22, 2019 9:58 pm quote
You're right to be concerned. When finishing a jetting set up and being left with one niggle, can end up meaning the whole set up is wrong. The only way to fix the niggle is to change a fundamental part means a whole re jet. The SI carb is like that.

Your plug looks too dark in general. When rolling off at speed and then back on is a good test for the pilot jet but as it is affected by the atomiser and main the issues could be any or all of them. Hard to decide between rich and lean. Rich feels heavy then clears and weak more like cuts out then goes. Try a BE3 first and see when happens.
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Tue Apr 23, 2019 5:07 am quote
Jack221 wrote:
You're right to be concerned. When finishing a jetting set up and being left with one niggle, can end up meaning the whole set up is wrong. The only way to fix the niggle is to change a fundamental part means a whole re jet. The SI carb is like that.

Your plug looks too dark in general. When rolling off at speed and then back on is a good test for the pilot jet but as it is affected by the atomiser and main the issues could be any or all of them. Hard to decide between rich and lean. Rich feels heavy then clears and weak more like cuts out then goes. Try a BE3 first and see when happens.
Actually, stock for stella is E3 atomizer. I will go back to that first and recheck everything. Not sure how E3 differs from BE3. Jetting really is an art form. takes a while to be able to discern the miniscule differences in symptoms. Just when I think i'm understanding it, I turn out to be all thumbs!
Hooked
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Tue Apr 23, 2019 7:29 am quote
Quote:
Even if your VBB has been converted to 3 port (which is unlikely), it still won't make enough heat to need more than a B6 plug.
Jack - tks - had missed this until t'day.

Swiss - following along with interest.
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Tue Apr 23, 2019 7:05 pm quote
Oh boy, all i did was change from be1 to e3 (stock) atomizer and all hell broke loose with my jetting. I can't get it to idle steady anymore. It hangs lazy terribly. It goes from steady idle on center stand to high idle when i take it off stand. Also leaning the bike either side affects the idle, and now the symptoms i was just getting last posts are way worse. Wondering if i should keep trying with this stock atomizer or go back to the be1 which was working well except that one small spot. Maybe i can dial it it with air mix screw better with the be1.
Molto Verboso
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Tue Apr 23, 2019 11:12 pm quote
Now you need a bigger pilot jet. This is an improvement. The stock pilot was seeming like it was too big. Now it doesn't
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Wed Apr 24, 2019 9:34 am quote
Jack221 wrote:
Now you need a bigger pilot jet. This is an improvement. The stock pilot was seeming like it was too big. Now it doesn't
In honor of bitza, i worked on the jetting this morning before work. I went from stock 40/130 idle progressively larger two idle jets to 38/120 and then 45/140. I am 3.75 full turns out on the air mix screw. I believe i need to walk it back in some as i have four stroking in the lower quarter throttle. Plug is still rich but back in the chocolate range.

I find it amazing that simply changing the atomizer from be1 to e3 made such a huge difference as when i visually compared them they are almost identical with the main jet side having same number and looks to be same size holes. The only difference is the air corrector side has 2 holes instead of 4 for the e3 and they appear to be same size. I'm probably taking a huge inaccurate guess here but maybe for each hole difference in the air corrector side of the atomizers equals one size idle jet. That's the only correlation i can visually see.

I have a suspicion my main jet may be one or two sizes too rich now after checking plug on wot run, but i will wait till i can pin down the air mix screw settings with the idle jet to get least four stroking with good color plug at quarter throttle before i make any changes with the main. I know it's not lean so I'm not worried about that.
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Wed Apr 24, 2019 9:49 am quote
I just realized i'm basically back where I started before i brought up this issue with lower quarter throttle. Same idle jet, same main jet.. Only difference is atomizer from be1 with air mix screw set to 1.375 full turns out....to e3 with air mix screw set to 3.75 turns out.

So the difference is not two idle jets, but somewhere around 2.5 turns out richer on the air mix screw for the change in atomizer.

It helps to keep an Excel spreadsheet of each revision of my jetting so i can slowly start to understand what each change affects!
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Wed Apr 24, 2019 11:41 am quote
In my Excel spreadsheet I've got the Stella stock jetting, suggested corrected jetting which is the stock px jetting and then all my iterations of jetting changes. I've come up with a way to visualize and understand the overall Richness of a jetting setup by figuring out the Richness value of each jet stack, then taking the average of those two stacks to come up with the overall Richness. I'm sure my way is not entirely correct as i have no idea how to account for atomizer or air mix screw setting on this scale. But in looking this sheet over, it seems to make sense with my experiences thus far.

Stella stock jetting (130/40, 140/e3/94) overall Richness is 2.369680851
Stella corrected jetting (160/55, 160/be3/100 = px stock jetting) overall Richness is 2.254545455

When i went back down to Stella stock idle and e3 atomizer which caused mayhem with my idle and jetting yesterday, that setups overall Richness was 2.325

Going back to my optimized idle jet that i had last week, with only the atomizer changed and more turns out of the air mix screw, my overall Richness is at 2.255555556 which is almost exactly at the Stella corrected jetting that mirrors the px stock jetting. So i have arrived at that magic number through different means, but with the addition of a performance pipe. I assume this number is static given the top end hasn't changed, but the jetting shifted to fit the rev profile of the pipe with higher top end power = higher main jet and on the lower end idle jet leaned out to compensate for the loss of power. Sip road xl pipe had higher rpm needs and loses a little torque at the bottom end.

Not sure if this all means anything but i feel like it helps me visualize things on a rudimentary level.
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Wed Apr 24, 2019 1:50 pm quote
Maybe there is something to this theory.. i just did the math on the stock jetting for the malossi 166 top end i haven't put on yet. It's overall Richness is 2.041806...... which is 10% more rich than the stock px 150 jetting. This lines up with the 10% of increased volume of the stock 150cc engine up to a 166cc engine. With that said, i think it makes it easier to ballpark my eventual jetting when i install the malossi by figuring out the percentage increased Richness of my current setup over stock 150 and apply that to the stock settings for the malossi.
Molto Verboso
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Wed Apr 24, 2019 11:55 pm quote
There is quite some differeance between a E3 and a BE3. If you stick with the E3 the main jet will need to reduce size until the WOT is like before. Once you get to this point, then start work on the pilot jet and mix screw. Good practice for doing it all again on the 166.

Generally your theory isn't wrong but will only get within 10% and a good guess would get that close.
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Thu May 16, 2019 10:30 pm quote
Jack221 wrote:
There is quite some differeance between a E3 and a BE3. If you stick with the E3 the main jet will need to reduce size until the WOT is like before. Once you get to this point, then start work on the pilot jet and mix screw. Good practice for doing it all again on the 166.

Generally your theory isn't wrong but will only get within 10% and a good guess would get that close.
Down to a 97 main jet with the stock e3 atomizer. Plug a little rich but i think it's the idle jet set a little high so I'm going to walk it down an eighth of a turn till it's fully chocolate and not so dark again. Idle jet set to 7 half turns out on a 45/140. Pulls strong from low down up through wot. Finally hit a true 60mph with Max 7100 rpm in fourth gear at the current jetting.

Definitely ready to move on to the malossi with its own thread started the other day where i will continue the jetting for that.
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