pudrev3 Posted August 29, 2015 Report Share Posted August 29, 2015 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 Quote Link to comment Share on other sites More sharing options...
billyt Posted August 29, 2015 Report Share Posted August 29, 2015 Change main jet to one step richer. Quote Link to comment Share on other sites More sharing options...
2stroke4stroke Posted August 29, 2015 Report Share Posted August 29, 2015 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? Quote Link to comment Share on other sites More sharing options...
evoalien Posted August 29, 2015 Report Share Posted August 29, 2015 A just air mixture screw Quote Link to comment Share on other sites More sharing options...
pudrev3 Posted August 29, 2015 Author Report Share Posted August 29, 2015 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 Quote Link to comment Share on other sites More sharing options...
wpatterson Posted August 29, 2015 Report Share Posted August 29, 2015 The rubber inlet pipe can also cause the same if loose or cracked 1 Quote Link to comment Share on other sites More sharing options...
lineaway Posted August 29, 2015 Report Share Posted August 29, 2015 Wpatterson is correct. Check the carb boot. That is a lousy tight fit and tears easily. Quote Link to comment Share on other sites More sharing options...
pudrev3 Posted August 29, 2015 Author Report Share Posted August 29, 2015 Ok will do cheers guys Quote Link to comment Share on other sites More sharing options...
timp Posted August 31, 2015 Report Share Posted August 31, 2015 Mine backfires a lot when throttle is shut on the road or going down hills. Do you have that as well? Quote Link to comment Share on other sites More sharing options...
billyt Posted August 31, 2015 Report Share Posted August 31, 2015 (edited) 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, 2015 by billyt 1 Quote Link to comment Share on other sites More sharing options...
timp Posted September 1, 2015 Report Share Posted September 1, 2015 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! Quote Link to comment Share on other sites More sharing options...
pudrev3 Posted September 1, 2015 Author Report Share Posted September 1, 2015 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 Quote Link to comment Share on other sites More sharing options...
timp Posted September 2, 2015 Report Share Posted September 2, 2015 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! Quote Link to comment Share on other sites More sharing options...
pudrev3 Posted September 4, 2015 Author Report Share Posted September 4, 2015 Put new plug in dropped pin to bottom done nothing !!! p****d right off now Quote Link to comment Share on other sites More sharing options...
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