Now backfire !?

[Deleted]

After i install my new exhaust with my 72cc kit, in the morning or when the motor is cold, when i run and when i slow down the scooter make some "Backfire", not a "Bang or Pow" but a "Pffft" sound!?

But when the motor is hot, when the choke is of, everything is ok!

Is it possible my mixture screw adjustement is not good?

The adjustement is at 1¼ open, if i open more, i can't have a idle speed when the motor is cold...

Pilot jet: #35
Main Jet: #88

Thank's!

[marshinman]

Sounds more like a timing issue.

[felliott]

Check for a vacuum leak around the the rubber elbow and the insulator under it. Also a exhaust leak can cause back firing.

[Deleted]

I re-adjust the A\F mix screw at ½ open and it look ok now, no more back fire. At idle speed the spark plug come black and after a top speed i do a plug chop and the plug is much better! (see pics)





I have this cover on the top of the carburetor and somebody said it was to keep heat in the carburetor!?
Is it better to keep there or remove thsi cover???

[ososlow]

mine does not have one there. imo it seems like it would trap heat around the carb though