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2007 KXF250 Won't Start After Shimming

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Hi There!

If you're viewing this then you're either stuck in the same position as me, or you're handing down your well appreciated knowledge!

First of all, I'm new to ThumperTalk, what a cool forum this is!

But let's get to it; Kawasaki KXF250 2007...

History:

I bought this bike in January, it was a bit tatty, but I saw it as a brilliant bike to finally get into Motocross full time, rather than just messing around on friends bikes. So my Suzuki Intruder was sold & I went off to purchase it.

Whilst out of action with a dislocating shoulder operation, I decided to pull the bike to bits and fix all the issues it's had. Now I'm a Maintenance Engineer, so as you can guess lack of maintenance can really bug me. So the whole bike has had a full strip down. I came to check the valve clearances & they were all out of tolerance, which explained why you'd struggle to start it & it wouldn't idle brilliantly. So the engine came out, I adjusted the valves via shims, which brought them all back into tolerance; along with an oil leak I cured. I was feeling pretty stoked by this point! 

So the engine went back in, the carb had a full strip down & clean, which was filthy, but now it looks like the inside of a watch. Diaphragm checked for any rips & tears, or pin pricks. 

All got loaded back into the bike for the first start. I turned the engine over by hand first to make sure I wasn't about to smash the valves into the piston. All good.

Primed with fresh fuel, I tried to kick it over. Nothing. Second kick it backfired. From that point onwards it's not tried to even start.

Ive checked all the usual suspects, good spark no leakage, it has fuel, carb seems all okay & doing its job. Timing is dead on, confirmed TDC by sticking screwdriver down cylinder & rocking the crank. All earths are spot on too. 

Now im seriously puzzled, it has everything it needs to fire, but it's not even trying. Any advice, help & ideas would be brilliant so don't hesitate to fire anything across! Cheers guys,

Nick.

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I realize you state the time is "dead on" but, if the valves are in spec, spark and fuel are good....I would really go back and triple, quadruple check that timing. The backfire is what makes me suspicious.

Edited by mxr73

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4 minutes ago, mxr73 said:

I realize you state the time is "dead on" but, if the valves are in spec, spark and fuel are good....I would really go back and triple, quadruple check that timing. The backfire is what makes me suspicious.

Thanks for your reply mate.

Am I correct in saying if the bike was to back fire, this would indicate the exhaust valve opening too early?

 

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Correct. Timing advanced too much and you'll get a backfire through the carb....intake valves open. Timing retarded too much....backfire through the exhaust. Extreme lean condition can also cause a backfire but you can usually get the engine to run, albeit poorly.

Edited by mxr73

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13 hours ago, mxr73 said:

Correct. Timing advanced too much and you'll get a backfire through the carb....intake valves open. Timing retarded too much....backfire through the exhaust. Extreme lean condition can also cause a backfire but you can usually get the engine to run, albeit poorly.

Awesome cheers dude!

i will have a crack at it in the next few hours & let you know how I get on :)

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