Sat Nov 20, 2021 10:30 pm

Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 3050
Location: London UK
 
Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 3050
Location: London UK
Sat Nov 20, 2021 10:30 pm linkquote
Was probably leaking at the carb. Peppy will come back. Stick with the 55/160 but be careful as it might go lean if the weather changes.

So now AC120 BE4 MJ122 55/160 ? Vortex and bellows to frame?

Go back and try the main jet again. WOT runs in 2nd gear. Be sure the jet is so rich it won't rev out, then reduce a jet at a time until you like it.
No point working on anything else if the main jet is wrong.
Sun Nov 28, 2021 8:46 pm

Hooked
Owned Vespa Rally 200, V90, Li150 series II...now a PX200
Joined: 26 Jun 2018
Posts: 191
Location: Fukui, Japan From San Diego
 
Hooked
Owned Vespa Rally 200, V90, Li150 series II...now a PX200
Joined: 26 Jun 2018
Posts: 191
Location: Fukui, Japan From San Diego
Sun Nov 28, 2021 8:46 pm linkquote
Jack221 wrote:
Was probably leaking at the carb. Peppy will come back. Stick with the 55/160 but be careful as it might go lean if the weather changes.

So now AC120 BE4 MJ122 55/160 ? Vortex and bellows to frame?

Go back and try the main jet again. WOT runs in 2nd gear. Be sure the jet is so rich it won't rev out, then reduce a jet at a time until you like it.
No point working on anything else if the main jet is wrong.
Rained all week and didn't have much time, but here's where I'm at. Started with a 130MJ, but I am back at 122. The 125 felt ok, but that 4000 rpm sputter is back. It's also only revving out to about 69-71kph. With the 52/100 I was topping out a little quicker at about 74. Not really sure on the temps. I've been getting around 240F during longer runs cruising at about 60kph. I feel it will hit about 260 like before, but it gets there a lot slower.
Sun Nov 28, 2021 10:19 pm

Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 3050
Location: London UK
 
Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 3050
Location: London UK
Sun Nov 28, 2021 10:19 pm linkquote
Still running pretty cool. Get a deep plug picture from a 30 second WOT in 2nd gear. New plug in a warm engine.
I think you can go down to a 120 main jet. Once the main is done the pilot is easier to get right. Then final trim the main (if needed).
Sun Nov 28, 2021 11:19 pm

Hooked
Owned Vespa Rally 200, V90, Li150 series II...now a PX200
Joined: 26 Jun 2018
Posts: 191
Location: Fukui, Japan From San Diego
 
Hooked
Owned Vespa Rally 200, V90, Li150 series II...now a PX200
Joined: 26 Jun 2018
Posts: 191
Location: Fukui, Japan From San Diego
Sun Nov 28, 2021 11:19 pm linkquote
Jack221 wrote:
Still running pretty cool. Get a deep plug picture from a 30 second WOT in 2nd gear. New plug in a warm engine.
I think you can go down to a 120 main jet. Once the main is done the pilot is easier to get right. Then final trim the main (if needed).
Problem is I have no place to do a 30 second WOT at the moment. Only place is covered in leaves.

Anyway I went for another ride today. I noticed that with the 4000 rpm issue only happens 1/4 throttle or less. I don't remember having this issue before. I went back up to 128 just to see how things felt. The 128 actually feels better. A lot more snappy, but at 1/4 throttle and around 4000 rpm it feels boggy. It actually stalled out in second once, but past 4000 rpm, it feels fine again.
Sun Nov 28, 2021 11:35 pm

Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 3050
Location: London UK
 
Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 3050
Location: London UK
Sun Nov 28, 2021 11:35 pm linkquote
This is what makes it hard to do without and sound recording. After fixing the air leak it was fairly safe to assume it would be rich. Obviously it was lean before and still lean now.
For anyone reading this when doing a main jet; take the MJ up in size until its un-ridable, so rich it cuts out, absolutely no chance its anything else but totally flooded, as the throttle gets near to WOT, spluttering like mad and trying to die. Then start reducing the jet size. Saves a lot of time.
Rich and lean symptoms are so similar it can be very difficult, even I get it wrong, not often but 40 years of tuning and it still happens.
Mon Nov 29, 2021 12:37 am

Hooked
Owned Vespa Rally 200, V90, Li150 series II...now a PX200
Joined: 26 Jun 2018
Posts: 191
Location: Fukui, Japan From San Diego
 
Hooked
Owned Vespa Rally 200, V90, Li150 series II...now a PX200
Joined: 26 Jun 2018
Posts: 191
Location: Fukui, Japan From San Diego
Mon Nov 29, 2021 12:37 am linkquote
Jack221 wrote:
This is what makes it hard to do without and sound recording. After fixing the air leak it was fairly safe to assume it would be rich. Obviously it was lean before and still lean now.
For anyone reading this when doing a main jet; take the MJ up in size until its un-ridable, so rich it cuts out, absolutely no chance its anything else but totally flooded, as the throttle gets near to WOT, spluttering like mad and trying to die. Then start reducing the jet size. Saves a lot of time.
Rich and lean symptoms are so similar it can be very difficult, even I get it wrong, not often but 40 years of tuning and it still happens.
I did start pretty high. At about 130, it was ridable, but still boggy through out the rave range. I liked the 128 except for the 4000 rpm stutter, so I figured I should keep going down. The stutter before wasn't dependent on my throttle position, or it wasn't as noticeable. I felt the 122 got rid enough of the stutter but didn't feel as peppy as before the air leak.
Mon Nov 29, 2021 1:34 am

Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 3050
Location: London UK
 
Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 3050
Location: London UK
Mon Nov 29, 2021 1:34 am linkquote
When doing an SI carb, maximum rpm is more important. Wide open until the revs level off. At this point decide whether its rich or lean. Any less than full rpm and you're just guessing. If there was terrible revving through treacle type spluttering and two sizes smaller main jet made it just burble, then one more size smaller and you're done. On a set up like yours there's only about jet 10 points between un-rideable (can't ride it and going home at 1/4 throttle rich) and perfect.
If 130 was obvious slight rich but rideable, 128 is ok, then 125 could be the one.
Once the main jet is at this point, any other symptoms are something else.
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