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CRF250R Runs, pops & bangs then stops

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Hi Guys, 2008 CRF250R Runs for about a minute then stops like its out of gas. Wont start again until completely cold. Valve clearances are spot on. Checked spark as soon as bike stops and get a 20mm blue spark across the tester. Stripped the motor completely. Has not long been rebuilt with new piston, con-rod & inlet valves. I replaced the crank & balance shaft bearings. Fitted new seals on crank. Stripped valves, replaced stem seals & relapped valves. Motor has good compression. Stator is nearly new (genuine Honda)

 

Can the one way valve be fitted wrong way round? if so will it cause probs?

 

Can crank seals cause probs?

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Did you have the valve seats angle cut to match the valves?

 

If not, they will leak as soon as the un-like metals expand at different rates.

You have to angle cut them so when they heat up, they seat better, not worse.

Edited by TheKoolAidMadeMeSick

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No didn't cut the seats as the bike ran fine all season, just stripped cleaned and very lightly relapped them. The previous owner had just replaced them. What your saying makes sense, I have another new head gasket so might pull the head back off. The carb has been modified by Honda Hamilton. They drill out the hot start hole, change the AC Pump cam angle, different needle & jets..... its been starting all season after a new stator & carb mods. Just out of the blue started popping and banging.

Thanks For the input

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My bike is doing the same thing on a fresh rebuilt head (built by one TT best engine builders) I did shim the valves myself. Thinking I need to clean the carb. Or maybe I shimmed them to tight. It starts fine gets warm starts running bad and dies won't start until it is cold again.

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The bike only has 60hrs on it. The bike was running fine until the head let go. It was sitting for about a year so I was leaning towards carb issues. I do have an extra stator I can try out.

Edited by proform

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