carb tuning help By bcgreatness (Read 729 times)

[bcgreatness]

i own a roketta md-74-150cc and just got my hands on a new carbon fiber exhaust with header pipe and quite amazed that i didnt have to bend or modify any part of my scooter or the pipe to get it to bolt up. i know enough to adjust the carb's lean/rich to eliminate backfire but no matter which way i turn the pin it still backfires. was wondering if anybody could help me with the tuning or should i look up the carb specs to see how many turns out i have to turn when i screw it in all the way? was wondering what settings everybody has luck with. reason why im worried about it is the muffler gets very hot and is already forming a black spot which indicates to me that it is definately not tuned right =( any help would be appreciated. most humble thanks to all who apply their words of wisdom. =)

[alleyoop]

Most likely it is leaking by the Header Flange, It is running LEAN sucking in air. Did you put in a New Header Gasket? When you put the Flange onto the Motor you must tighten the NUTS evenly so it seals evenly otherwise it will be a little cocked and it will leak and backfire, which is not good.

Also you probably need to up jet your carb to at least a #112 MAIN JET, leave the Pilot Jet alone for now they usually come with a #35 which should be good enough.
Alleyoop

[JR]

Ah alley beat me to it! I alrready thought I had a backfiring tutorial in the tech section and while I was digging one up to list he snuck in on me!

But I'll echo what he said plus add that just about every single cause is outlined in this nice tutorial I found.

Also when you put the new exhaust on did you go back and reitighten flange bolts? Lot's of times after a new gasket heats up they shrink causing it to suck air ?

Keep us informed we are here to help!

thescooterprofessor.proboards.com/index.cgi?board=gall&action=display&thread=850

JR