Air/Fuel adjustment question

Pštros · 09-21-2013, 09:36 PM

I have a 2013 Puma Valentine 150cc (the 1966 Vespa clone). I was into a new carb from the dealer within 50 miles for a malfunctioning choke. New carb made a huge improvement but still some acceleration issues. I watched about a dozen You Tube videos and tried adjusting the fuel/air screw.

After warming up for 10 minutes I find the bike runs fine with the screw ALL THE WAY IN. I don't suspect that's how it's supposed to work. No change to the acceleration after several 1/8 to 1/4 difference settings. Maybe a leak?

This is important because my wife also got a new BMS 150cc. We replaced the carb, before 50 miles, and it runs very smoothly and has great power. Why is mine a pig?

Thanks from a new member and first time poster!

blueboy5000 · 10-11-2013, 09:14 AM

You have a LARGE air leak (vacuum leak). Proper carb setting is 2-1/4 to 2-1/2 Turns out from seat.

Using a spray bottle of water, start bike and then spray around the intake manifold and vacuum hoses and listen for DECREASED rpms. When the rpms decrease, you've found you leak.

Also, make sure your DIAPHRAGM in the carb is seated properly, and sealed and free of rips in the membrane.

skuttadawg · 10-12-2013, 03:53 AM

http://www.iwt.com.au/mikunicarb.htm hope this helps

10-11-2013, 09:14 AM	#2
blueboy5000 Join Date: Jul 2011 Location: Connecticut Posts: 493	You have a LARGE air leak (vacuum leak). Proper carb setting is 2-1/4 to 2-1/2 Turns out from seat. Using a spray bottle of water, start bike and then spray around the intake manifold and vacuum hoses and listen for DECREASED rpms. When the rpms decrease, you've found you leak. Also, make sure your DIAPHRAGM in the carb is seated properly, and sealed and free of rips in the membrane. __________________ 2011 Roketa MC-23-150 4T 150cc 157 qmj 24mm carb w 115 main jet and paper cone air filter Manual petcock w Tygon fuel lines Scrappy Dog Scooters Retro-slash stainless straight-thru exhaust RED spring clutch Adjustable CDI (brand unknown, it's blue and red and works great!) KOSO high performance variator w 12g sliders Gates Powerlink 835-20-30 belt GPS verified 65mph on flats.
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