155 main jet?

[Usafdolfo16]

First post!! And it's a problem lol =(

I have a 2008 150cc gy6 sunl that has about 300 miles on it. The scooter runs great with no errors stock. I recently installed a free flow exhaust and performance air filter so I knew I had to change out the main jet. The stock one was a 105 and the spark plug was bone white. So I installed a 125 jet and now the scooter can get up to 57 mph but bogs when I gun the throttle quickly then starts up again. Feels like I loss the start speed a lot. So I took out the carb (and by the way it's a new carb) and installed a 135 jet and it felt a little better but not really. Took out the plug and it was a little less white. Had a dark spot that was almost made it look dirty and Not brown. I know I was running lean since I got the muffler installed first and ran the scooter and my muffler tip caught on fire from being so hot.....Maybe Im getting too much air with the new filter or do I need to up jet to 155? Don't know what to do. I live in Las Vegas so 2000ft ish elevation. Please any one help!

[rks]

You certainly don't need a jet anywhere near that size to feed a 150cc scooter. You must have some major air leaks between the carb and the head.

I run a K&N cone filter on my scooter.......stock exhaust.....and a 115 main jet is just right. I don't care what you have done to your exhaust....it will not require as big of an increase in jet size as you have already made.

I have a two cylinder motorcycle, with a separate 32mm Keihin Carb for each of it's 375cc cylinders. Came with conservative 125 mains.....I have upped them to 135.

My 400cc Yamaha ATV has a Mikuni 33mm carb.....it has a 112.5 Mikuni main jet, which is equal to a 128 main in a CVK, or Keihin carb.

Better check that manifold and such.

[Usafdolfo16]

You are 100% correct...I went to a 118 jet and it was great but still bogged on the quick acceleration...switched to 115 and now it's awsome...got some crackling in the exhaust here and there but it runs great...thanks