Missing bad on the topend of 400ex

[Sick0]

my 400ex is missing real bad on the topend( anything over half throttle). I've been dealing with this problem since I blow a head gasket in august after having a 440 kit installed about a month before. I hate to say it but I rode a while with a blow head gasket (about a week) just try to mess with jetting not really know what was wrong with it. Well I finally came to the concusion it was my head gasket. So put a new head gasket in, and set did the same thing. I messed with diffrent jetting, tryed to carbs. Both of witch I had set real good for my set up right before the I blow the head gasket, so I know I had to be close on jetting. I tryed running a diffrent exhaused, cheacking for air leaks. I gave up and open the motor up again. I looked close at the piston and look like one of the exhause valves came contact with piston. I thinks from theblow head gasket. The was barely hit the piston and the valve looked good. But I thought maybe I burn up the rings and damage the cycinder from riding on it with a blow head gasket. So installed a diffrent cyclinder with a fresh piston.

well the problem is still happening. The motors sounds pretty good until it starts to warm up and then it will start to choke. I also notice( i could be wrong) smoke when its does this. So I'm geussing this probly some thing to do with the valves. But I barrowed a friends cdi box and coils and going to try them to atleast rule that out. Has this happen to anybody else and /or does anybody have a clue what the problem is.

[Taco]

pull the valves and make sure they are straight

[Sick0]

AS of right now. I think its the cdi box that went. It runs pretty good with out and I let warm and ran it for about 20mins with no problems. the sxmokes appears to be coming form a small oil thats easily fixable. I going to take it and run it out on the lake and give a good test.

The funny is, I was revving getting pissed it was cutting out on the very topend set. it turn out it was just the rev limiter. These 400 don rev like the yfz and I've gotten use to the yfz so 400ex doesn't sould it was running as good.

[idahoquad]

Originally posted by Sick0
AS of right now. I think its the cdi box that went. It runs pretty good with out and I let warm and ran it for about 20mins with no problems. the sxmokes appears to be coming form a small oil thats easily fixable. I going to take it and run it out on the lake and give a good test.

The funny is, I was revving getting pissed it was cutting out on the very topend set. it turn out it was just the rev limiter. These 400 don rev like the yfz and I've gotten use to the yfz so 400ex doesn't sould it was running as good. i had a broken bolt head on my cdi box and it would cut out when it heated up very agravating :mad:

[Sick0]

Well because of all of this. I missed a race at a track I want to ride. I lose points for the year, I took out the 440 kit in the 400ex and the biggest thing that end up happening is i bought a yfz so I had something to ride for the nats