QuestionHello Mark .I have recently modified a yfz 450 , Yamaha atv . I have removed the baffle from the stock exaust canister , removed the air box lid (per suggeston from pro in 'dirtwheels mag.),installed a slightly larger main jet , (apx.165-.170 ,- can't remember which one I put in last while experimenting/testing i.e. goofing around with bike/having fun).)So , anyway ,no matter which combination of needle setting/jet size , or any other adjutment , pilot jet,low idle mix , acclerator pump , ect. ,nothing will keep it from dying instantly when I blip the throttle quickly ! What am I overlooking ? If you just slam the throttle wide open , the engine just seems to suffocate and dies right away . I've looked into everything I can think of and it will still do it . The ignition timing and valve lash are spot on ! What's the deal ? If you slowly throttle up at a very smooth controlled rate , it will rev up great ! You can hold it at a steady 3000 rpm and it sounds beatifull ! It seems like it would be the accelerator pump , but it's squirting plenty of jiuce . I think I'm going crazy .Would this issue be symptomatic of a lean condition , or rich ? could a free flowing straight tube "racing" exuast/silencer resolve the problem ? Could it be too much resistance in back pressure from lame stock pipe with baffle removed ?
Any possible sugestions would be extremely appreciated .
Sincerely , James May
AnswerHi James,
The air-fuel mixture needs corrected. I suspect the air intake needs some restriction to improve throttle response.
My advice is to undo the carburetor tuning you have done and re-do the tuning. Make one change at a time to know what effects each change has on performance.
Undo the tuning one change at a time, too and then test ride. You may discover the problem this way as well.
What works for one application in a specific environment may not work for all in varying environments.
I return tech information files via email. There was no email with question as requested.
Respectfully,
Mark Shively
