Wed May 11, 2022 6:22 am

Member
1960 VBA with '82 PX125E
Joined: 26 Jan 2021
Posts: 8
Location: New England Babey!!
 
Member
1960 VBA with '82 PX125E
Joined: 26 Jan 2021
Posts: 8
Location: New England Babey!!
Wed May 11, 2022 6:22 am linkquote
Hi guys! I have a mostly stock PX125E engine on a VBA frame. To fit the 10in wheelbase conversion I had to upgrade the exhaust because the stock one would not fit around the tire. The engine has a SI 20/20 Carb with a 160/BE3/98 main stack and a 45/140 idle jet. I can't seem to get rid of the bog/power loss that happens when I reach 1/4-1/3 throttle no matter where I set the idle adjust screw (from 1/2 turn out to 4.5 turns out). The aftermarket exhaust I bought here: https://www.scootermercato.com/Scooter-Parts/Simonini/SIM40301BL. Does anyone have a suggested starting place for an upjet? And do I need to upjet both, or just the main jet?

Last edited by BananaOne on Wed May 11, 2022 7:09 am; edited 1 time in total
Wed May 11, 2022 6:43 am

Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8848
Location: Atlanta, GA
 
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8848
Location: Atlanta, GA
Wed May 11, 2022 6:43 am linkquote
The idle jet will have its biggest impact from "closed" to ~1/4, where its impact becomes dwarfed by the main jet circuit. If you just changed the exhaust you can probably leave the idle jet size alone and compensate with the mixture screw to ensure safe closed-throttle behavior (stock should be ~1.5 turns out, so you'll be looking at at least that much), but you'll definitely want to update the main with a performance exhaust. Start high and work down
Wed May 11, 2022 6:48 am

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 08 Stella (for now)
Joined: 16 Jun 2011
Posts: 5979
Location: Nashville
 
Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 08 Stella (for now)
Joined: 16 Jun 2011
Posts: 5979
Location: Nashville
Wed May 11, 2022 6:48 am linkquote
If you're ordering jets, pick up a BE5 atomizer as well. that will help with the lean transition at 1/4 throttle as well as the mid-range, which is probably also lean as well. This matters because when you roll off WOT, if that mid-range is too lean, that'll kill the top end and leave you stranded on the off ramp.

And if it's too rich at mid-throttle, you can go back to the BE3, but for $5, it's cheap insurance since you're already ordering.
Wed May 11, 2022 6:54 am

Hooked
2005 Stellalossi 177 Fe
Joined: 14 Jun 2020
Posts: 269
Location: MA
 
Hooked
2005 Stellalossi 177 Fe
Joined: 14 Jun 2020
Posts: 269
Location: MA
Wed May 11, 2022 6:54 am linkquote
Bogging just past 1/4 - 1/3 throttle points to the BE3 mixer tube being too lean. Try a BE5 instead.
Wed May 11, 2022 9:00 am

Ossessionato
73 & 74 Rally, 76 ET3, 80 P200, 06 PX150, 61 Ser 2, 65 Silver Special, 86 Elite 80,90 V5N 50, 01 ET2, 2015 HD Road Glide Special, 2011 Ural Tourist
Joined: 18 Jan 2012
Posts: 4372
Location: Oceanside, CA
 
Ossessionato
73 & 74 Rally, 76 ET3, 80 P200, 06 PX150, 61 Ser 2, 65 Silver Special, 86 Elite 80,90 V5N 50, 01 ET2, 2015 HD Road Glide Special, 2011 Ural Tourist
Joined: 18 Jan 2012
Posts: 4372
Location: Oceanside, CA
Wed May 11, 2022 9:00 am linkquote
Let me confirm, did you leave the 10" tire on the PX motor, or did you change it to 8"?
Wed May 11, 2022 11:53 am

Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
Joined: 04 Aug 2014
Posts: 194
Location: Madeira Island
 
Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
Joined: 04 Aug 2014
Posts: 194
Location: Madeira Island
Wed May 11, 2022 11:53 am linkquote
MJRally wrote:
Let me confirm, did you leave the 10" tire on the PX motor, or did you change it to 8"?
I think the OP said he changed to 10", that's why he had to change the exhaust to accommodate the bigger wheels
Thu May 12, 2022 4:14 am

Member
1960 VBA with '82 PX125E
Joined: 26 Jan 2021
Posts: 8
Location: New England Babey!!
 
Member
1960 VBA with '82 PX125E
Joined: 26 Jan 2021
Posts: 8
Location: New England Babey!!
Thu May 12, 2022 4:14 am linkquote
Correct, I think the front fork I swapped in is from a stella, but I still haven't found a way to properly mount the mudguard, if anyone has an idea that would be appreciated. BE5 atomizer and a 102 and 104 main jet are on the way.
Thu May 12, 2022 5:58 am

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 08 Stella (for now)
Joined: 16 Jun 2011
Posts: 5979
Location: Nashville
 
Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 08 Stella (for now)
Joined: 16 Jun 2011
Posts: 5979
Location: Nashville
Thu May 12, 2022 5:58 am linkquote
BananaOne wrote:
Correct, I think the front fork I swapped in is from a stella, but I still haven't found a way to properly mount the mudguard, if anyone has an idea that would be appreciated. BE5 atomizer and a 102 and 104 main jet are on the way.
Pictures of what you're working with would help a lot. Basically, expect to drill holes and possible fabricate some mounting brackets. Nothing you can't solve with a drill, angle grinder, and metal stock. Bonus points if you can weld rather than bolt the brackets to the fork.
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