Modern Vespa

Hello guys. Its my plug too lean? My px seems to run fine. No loss of power or what. Just installed a SIP race pipe. Currently have a cast iron 177 polini and a 24.24g carb.

my current jetting:
idle jet: 50/100
air corrector: 120
mixer: be4
main jet: 120

Will be putting a vespower ignition next week also. Any tips would be much appreciated. Thanks!

You may be a little lean. Try a 125 main jet and see if it still revs cleanly.

I actually just put the 125. Will be riding it later. If it still has that color plug, it means i have to tweak the air mixture?

The 120 AC is already about as rich as you want to go. You'll need to drill the carb's float passage to get any benefit from a main jet over 125, though.

Are you 100% certain you don't have an air leak?

125 will be my max MJ. Will double check for air leaks! I already have the compression tool. I will update you!

Compression test reads at 105 psi.

Compression is one thing. Air leaks are another.

Incase of an air leak, will the compression go down and not steady?

No. That's just your gauge losing pressure.

IF you have an air leak, it's introducing air into the combustion chamber from a few possible places. Either the carb gasket, the carb box gasket, the cylinder head, base gasket, exhaust stub (p200), or engine seals.

Try this test- when riding, pull the choke out. If the engine runs better, you need to tweak the jetting OR you have an air leak. If the motor runs poorly, your jetting is fine and you need to ride more.

How many miles did you ride before you took the picture of the spark plug? Maybe do 20 miles and see what the color of the plug is. A true plug chop is where you ride at a certain rpm and kill the ignition. Then remove the spark plug, cut the threads and look at the base of the insulator. My 20 mile idea isn't exactly a plug chop, more to just see how the jetting is big picture.

With an otoscope you can avoid the work/trashing a new plug.

$20 otoscope/ear cleaner from Amazon. Snap off the scraper tool.

Seems low. According to Polini manual it must be 150 PSI.
Even my used DR with Malossi head shows 163 PSI.

105psi... that's not compression, that's squish?

I dunno what I'm talking about, but it seems way too low