98 yz 250 cutting out at top speed

I just bought this bike about a week ago and every time I pin it in 5th gear she dies about 20 seconds after doing so. When it cuts out, it dies completely, can't jump it or kick it over for about 5-10 minutes. It only happens in 5th. Engine was rebuilt about 8 hours ago (top and bottem end), compression is fine. Just had everything serviced, including fresh oil and coolent. Seems to hesitate a little bit in 1st and 2nd but it isn't to bad. I was reading around, and i've got 2 ideas as to what it could be, either overheating or a bad cdi box. I can't see it overheating, as I am riding in weather thats almost 0C (or 32F), and the cdi box was replaced about a year ago. Any idea as to why this is happening? When I try to kick it over right after it dies, there is little to no effort to kick it over. I have to wait a bit of time for it to be able to kick over again. Once it kicks over, she is perfect.

Engine was rebuilt about 8 hours ago (top and bottem end),

by whom? You or the seller?

by whom? You or the seller?

Seller. But the seller was good friends with a co worker of mine, and the person who rebuilt the engine is a reputable guy in town. Has great compression and doesn't have any knocks. I had brought it into my small engine mechanic for a complete look over, and the only thing he found that could be off is a bit of gunk on the power valve which he cleaned up.

Bump. Anybody have any idea?

I would be testing the cdi and the coil per the manual with a description like that.

I got a cdi and coil on order. Think it may be a bad seal somewhere? Where the engine when revving very high loses compression and thats why I can't start it for 5-10 minutes?

Double check your reeds. You might have a chipped or broken one...

Sounds like the coil is the issue. Try that before you install the CDI, you may be able to save yourself some money by returning it.

Edited by BDubb106

My 98 was doing the same thing when I got it turned out to be a broken bottom ring .

Thanks for the help guys. I'll update the tread when I pin point the problem for future reference. I'll start with the coil, then cdi, then clean the carb, then open the engine if all those fail.

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