Fuel issues/bike missing at 75/80kmh!!!

Hey all,

I only managed to do around 200km on my new 2004 WR450 (AUS) before having the exhaust changed over to a yoshi competition/offroad. When I picked up the bike from yamaha, the mechanic told me he wasn't happy with the jetting he fitted for the test ride, so he changed over the main jet for a bigger one but didnt have a chance to test it. He said if I have any problems with the bike backfiring i should return it to have the jet changed back to a smaller on. My problem it this....

I dont seem to have a problem with backfiring (unless im decelerating down a hill). When I gas the bike up a hill i have no loss of power or missing of any kind. My problem is when i do anything over 75km/h on the flat while applying minimal throttle (so just maintaining a constant speed at 75km/h on the flat) the bike seems to miss, or not get enough fuel. it's almost like the bike is pinging... seems lack of fuel or some kind. (loss of power for half a second or so).

Any ideas if the jetting might be causing this? I have tried different octane fuels in the bike, and like i said if im doing under 70km/h or if im gassing the bike up a hill (above 75k/h) there is no problem. it's only on the flat that im experiencing problems. i have played with the grey wire trick and see a "marginal" improvement running the YZ mapping (i mean maybe 76km/h without a problem), but still issues at 77km/h+

Any ideas would be appreicated :thumbsup:

Thanks,

ch0g

My 03 is the same, since there aren't many trails where I live I unplug the tps when I am on dirt roads or the street at home and plug it in for trails up north. Good luck.

You are actually rich on the needle. Drop it 1 clip to see an improvement.

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