Hey guys Got another problem I've got a beta Evo 300 4t 2014 , if I Rev it high it backfires loud is this normal? It does it nearly every time , ?any help would be much appreciated

Change main jet to one step richer.

If it didn't do it before then check for air leaks in the exhaust, possibly at the flange where it bolts to the head. You may notice a bit of burbling on the overrun when going downhill?

A just air mixture screw

Cheers folks I'll try the main jet first , air mixture is ok so don't think it's that , someone said they go through spark plugs so I'll bang a new one in hopefully do the trick

The rubber inlet pipe can also cause the same if loose or cracked

Wpatterson is correct. Check the carb boot. That is a lousy tight fit and tears easily.

Ok will do cheers guys

Mine backfires a lot when throttle is shut on the road or going down hills. Do you have that as well?

If it backfires when shutting off the throttle or going down hill then your pilot jet is way to lean, richen up the pilot jet.

 

Edited August 31, 201510 yr by billyt

If it backfires when shutting off the throttle or going down hill then your pilot jet is way to lean, richen up the pilot jet.

It's running nicely at the moment so I am a bit unsure if I will gain one and lose another!

Somebody told me that they run them lean to pass emotions when they are new which makes them run badly , backfire drop the pin down I dropped mine down one and it's running a lot better just waiting for my new plug and I'll drop it down to bottom setting , that billyt knows his stuff

So that narrows it down to adjusting the needle, adjusting the mixture screw, putting a bigger pilot jet in or putting a bigger main jet in!

Put new plug in dropped pin to bottom done nothing !!! p****d right off now