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1998 yz250 surging done a ton of tests

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hey guys

motor was rebuilt 28 hours ago

the motor ran great for 20 of those hours


it surges from idle to 1/4 throttle.


if I put a crazy fat PJ 65 then it almost goes away.

the bike runs great with the choke on


 done a leak down test and it does not show anything


checked crank seals


swapped carbs with another great running bike so its not a plugged PJ or anything


done compression check. 190 psi


no leaks of coolant or tranny oil


I have sprayed the entire motor area with starter fluid and no changes. 


took the bike to a shop and they did the same tests.


the shop wants to spilt the cases to look round inside..


with the bike running better with a crazy fat PJ 65 .... and or with the choke on ,,, it would scream air leak or lean.


anyone ever had this before??????????????




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