My 04 wr450 cuts out when throttle is opened quick

I have a 04 WR450F with all the free mods (throttle stop, gray wire, uncorked, snorkel pulled).

When I open the throttle quickly the bike acts as if I had hit the kill button. The bike would die without a sputter if I were to keep the throttle open but if I let off the throttle a bit the bike snaps back to life as if nothing had ever happened.

I have tinker with jetting enough to think that the problem cannot be solved with jetting alone. I have adjusted my accelerator pump timing to speck and to both extremes without solving the problem. I have removed the carb and inspected the accel pump finding no obvious problems. I have used several different exhaust arrangements (stock corked and uncorked, big gun signature series) and it seems to me that the more open the exhaust is the worse the problem becomes (ie if I put the cork back in the problem goes away and the problem is worst with the big gun).

What the heck is going on? More importantly, how do I fix it?

I would say to try jetting changes first! Switch to a 48 or 50 pilot and put in a 40 leak jet. Some pipes flow so well that the bike has a lean bog at idle to 1/4 throttle it is most noticeable. Also make sure you set your idle at about 2100 rpm min. The pilot jet circuit will be rich for idle purposes but the bike just pulls better when lugging it around. I never idle mine for too long anyway ( that is why we have the e-start). The smaller leak jet is a must for a flowing pipe. I ran my stock pipe uncorked and my new FMF pipe with 2" opening and no insert. The FMF pipe made me change to a richer pilot and needle setting then I was using with the stock pipe. I like my bike set up so I can crack the throttle open from completely shut just above idle ( at low engine revs)and it wheelies in lower gears. You will find a lot of people with smaller pilots but they are usually on the 426 and earlier models which had to rich an ACV squirt. The 03's & 04's have a much smaller squirt and therefore the pilot jet and leak jet is more critical setting up to get the throttle response you want. If you have the JD kit switch to the blue needle in #4. I had to go from red 4 to blue 4 to get the new pipe to rip ( Normally i used blue for cooler weather)! Each bike is different with air box mods and pipes but the point here is to try it and evaluate the performance for yourself. :thumbsup:

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