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Discussion Starter #1
My derbi gpr 125 2009 is having some issues. I took it out one night and if I throttled too much the revs would drop but then kick in all of a sudden a split second later, this happened more and more over a 10 minute period until it got so bad I couldnt rev at all, I left it idling untill it cut out and hasnt started again since.

There wasnt any smoking or noises which seemed unusual.

I've verified spark and tried dropping fuel into the cylinder aswell as easy start through the intake, nothings given results so far, I bought a compression test but the attachments dont fit lol

I plan on pulling the valve cover off and verifying timing and its not a vavle stuck open.

Other than that has anyone got any suggestions on anything I can test which will lead me in the right direction? Im stuck as nothing is working
 

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Discussion Starter #3
It could be a dirty carb. Checking the valve clearance is a good idea.
Wouldnt it start on easy start if it was just a dirty carb?. I bought a new set of feeler gauges just for that purpose!, I also inteed to pull of the carb if vavles came up a miss. Thanks
 

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Think basics: Fuel, compression, and a good spark at the right time.

Putting liquid fuel into the intake isn't always a reliable test as it may not get vaporized enough to burn. Try some ether. If that doesn't cause it to pop I'd next check compression and spark. Try to get an idea what's happening before you start taking stuff apart, as you may miss clues when you remove parts.
 

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Discussion Starter #5
Think basics: Fuel, compression, and a good spark at the right time.

Putting liquid fuel into the intake isn't always a reliable test as it may not get vaporized enough to burn. Try some ether. If that doesn't cause it to pop I'd next check compression and spark. Try to get an idea what's happening before you start taking stuff apart, as you may miss clues when you remove parts.

I'd verified spark, I thought easy start spray in the intake eliminated a fueling issue. My last shot was a compression issue but as I say I couldnt get an attachment to fit so I was going to check the valves for movement/clearance. The basics seem to be coming back empty mate
 

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If you take the heads off and look at the vales before checking compression you won't be able to tell if you're losing compression through the rings or possible a blown gasket. You can do it that way, but it's easier if you do the comp. check first, and then a leak-down test if needed. That way you can usually pin point your problem before you get too far into it and hopefully save a few coins into the bargain.
 

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Yup, do the comp test first. Almost any auto parts store should have the right size adapter cheap.
 
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