Modern Vespa

Hello All

First time post but have been following and reading others post for the last year or so.

I've had my 1964 Allstate for about 7 months now.
Specs
150cc
12v Vape ignition
SIP 2.0 road
Spaco 20/15D
Jets
MJ 100
Air Corr. 120
Emulsion tube E1
Idle jet 42
Start jet 60

My question is about jetting with the SIP exhaust. After installing the exhaust I noticed a big difference in power. But am afraid of running to lean. I was curious if anyone here with similar set up has jetting set up that works? I did try a 102 Main jet but it sputters upon take off and if I'm at 1/4 or 1/2 throttle but it cruises at WOT. When I go back down to 100 Main jet it doesn't have the sputter. But the spark plug looks lean after a 15 minute ride with the 100 MJ.
If I do need or do go up on the MJ what would help out with the transition from 0 to 1/2 throttle sputter?

Any help will be appreciated

if that's a plug chop at full throttle that looks pretty decent to me.

the 20/15 is kind of a bastard to dial in. you can try a 140 and see if that clears up the transition, but you'll likely need to bump up to like a 104
a different diffuser E3 or 4 might help without any other change. I'd maybe try that first.

Thank you for the info. All I see for sale for diffusers is BE3 or BE4. Is there any difference with the E3 and BE3?

everything you wanted to know and then some!

check it out:

Wiki [D] Guide: SI Jetting Chart + How to Tune an SI Carb

Thanks again. Good right up but they don't say if E1 is same as BE1 for example.

look at the chart.

an E1 is richer than a BE1, on par with a BE5

at any rate, I'd probably try an E3 for your set up

Got it thanks

Before anything else I would just up the idle jet from the 42 to maybe 48.

I ordered more jets and will change one ket at a time to see if anything changes.

Thank you