Hi MateyHad the very same problem with my old WR,Check Air filter and clean if dirty but this sounds like a mixture problem probably running too lean.Check what slot the main needle is set at and take it down a slot to richen.then you could always take the carb off and check the pump cover diaphram and then generally check all the jetts and also check the vacum slider plate at the back as these can crack and break up as mine did and then shag a couple of vavles and piston these also make idling and general perfomance all over the place.also before you remove the carb check for any air leaks from the rubber collars that hold the carb in place .Could always check Thumper talk web site for addition info.Hope this helps?
Is it when you shut the throttle?
more often than not yes....
check the pump cover diaphram and then generally check all the jetts and also check the vacum slider plate at the back
What, and where, are these bits, as I don't recall seeing them on mine when I was spending months getting it to work as I want.
Pump cover is at the bottom of the carb 3 hex fixings , once the covers off theres a rubber diaphram that can split and collect dirt etc.Vacumn slider plate is i think exhaust side of the carb can only see it if the carbs off the bike once off the bike activate the throttle linkagage and you can see the plate and slider moving but make sure the carbs out of petrol as this does squirt out so watch yr eyesWorth checking the vacum plate as I've said earlier they're bout 90 odd quid from Allens,but if yrs looks damaged change it cos I had the top half rebuilt because of a damaged one.Hope this helps but I'm no way an expert, carbs are still a grey area for me
i had a similar problem on my 98 model wr 400, only i have blown two exhaust baffles out completely. the engine wont rev out , and the exhaust heats up instantly . It was running fine then on a ride lost power and blew the baffle out . I thought it was a fuel problem but have had carby apart , all seemed fine . It has a vortex cdi and i have changed to the yz timing , but it was running perfect . any ideas people ?
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