70cc atv problem

[minibikeman1180]

hi myatv only runs on choke and when you take the choke off i need to holdbit about 3/4 throtle to keep it runing also it goes and stops but it doesnt die as long as you have throttle also if you rev it it it backfires about 10-15 times
if any of you may know whats wrong let me know

thsnks, Joe

 

[b52bombardier1]

Two things. One - you probably have a clogged main jet in the carb that needs cleaning.

Two - you could have a vacuum leak between the carb and intake manifold. The choke is possibly compensating for the lean air getting in at the leak location. Spray some carb cleaner at the intake manifold joints with the engine running. If the rpm changes, you have a vacuum leak.

Rick

Two CT90 and two ST90 bikes