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99 TRX 400ex top end problem

1510 Views 2 Replies 2 Participants Last post by  KippaDR
Hey guys, I just got a 99 400ex last week and so far its been great on the bottom end. Its got the power I need when climbing on the hill trails. But ive got a problem when opening it up for top speed. Ive searched through the forums about the carb but my predicament is a little different than the ones I have read about.

I have full power at all times in the first two gears. If i punch it hard, there isnt any bogging down of the motor at all.....until i get to a certain SPEED in the higher gears. The motor will cut out and bog down like its getting too much or not enough fuel. If I shift up, I get full power with full open throttle until I hit that certain rpm in the next gear, then it does the same thing (it does stairstep, by that I mean, the higher the gear i am in, the lower the rpm when this problem occurs). Its not the rev limiter because I can get it to scream alot more in the lower gears. Opening up to full throttle slower doesnt seem to help. if it does help, top gear doesnt get to that certain rpm to make it bog down(at least with the amount of distance I had to work with) It MIGHT be a little bit worse when ive ridden it hot for a half an hour or so, but it was on different terrain(wash sand intead of asphalt) so its hard to tell.

I just did a full carb rebuild on it and there wasnt any change. It still does the same thing. I am just a couple of hundred ft from sea level. It has all the stock jets on it and as far as i can tell, its still the stock pipe and intake. I havent had a chance to do the spark plug test on it because im waiting for a couple of new plugs. Im just kind of looking for an alternate solutions while im waiting. Im wondering if this might be a common problem because everyone seems to be running larger jets. Im almost certain i need a bigger pilot jet because with the idle screw all the way in, it seems like I could get a better idol when its cold(its died once or twice after 3 or 4 minutes without touching the throttle) . Im thinking about getting a larger main jet to see if that helps. Fuel mixture screw is at 2 and 1/2 turns.. I put the ring on the needle in both higher and lower positions, but it still seems to run best on the 3rd notch(stock position). No smoke coming out of the exhaust at all.

Any suggestions? 0.o
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You really need to test this by looking at the spark plug. If the clip is in stock position with the stock pilot and at 2 1/2 out it sound like the pilot circuit is fine.
Stands a chance of being the low circuit or an inlet (air) leak.

When you rebuilt the carb what rebuild kit did you use? China junk from eBay/Amazon or OEM?

How do you define the term 'clean'..? Carbs need to be surgically clean.
Did you flush the fuel tank and fit and inline fuel filter at the same time?
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