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Old 10-12-2017, 05:09 AM   #1
Director59
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Backfiring and no power

Hi All!. I'm new to this forum and need a little guidance. I am a retired auto, truck and small engine mechanic and I am trying to fix my daughters boyfriends Suzuki '99 GZ250.

First of all this bike seems to be a Heinz 57 of a GZ250 as it does not have all the features the shop manual says it should have, i.e. missing a second throttle cable, electrical components missing and it looks like some spliced most of the wiring together.

The bike was leaking oil from the head gasket, so I purchased a rebuild kit and replaced the cylinder to block gasket, head gasket, cylinder head cover gasket, etc. Also replaced the spark plug. The bike worked fine for a while then it started to backfire. re-checked valve clearance and still had the same issue. Carb seemed to be dumping to much fuel, rebuilt carb, but still have the same issue. If this was a car or truck, I would check timing, but shop manual has no info for that.

The bike starts fine and runs great for about 5 mins and then wants to stall and if you give it throttle it backfires and has no power.

Can anyone point me in the right direction?

Thanks in advance,

Frank



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Old 10-12-2017, 05:29 PM   #2
derbydave
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When you rebuilt the carb did you drill out the plug and service the pilot jet circuit?
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Old 10-13-2017, 01:05 AM   #3
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Sure did. Adjusting it has no effect.
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Old 10-13-2017, 01:43 PM   #4
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How many turns out did you set the pilot screw? did you replace the O ring on the choke plunger? Check the float level? Attached is the only thing I could find regarding engine timing.
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Old 10-13-2017, 01:47 PM   #5
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What did you set the valve clearances too?
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Old 10-13-2017, 02:20 PM   #6
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Set Pilot screw at 1.5 turns out. I replaced the O-ring, double checked float level. Set intake valves @ .002 and exhaust @ .004
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Old 10-13-2017, 02:31 PM   #7
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I found my bike ran best at 2.5 turns out. What about compression? If that is good I would suspect electrical. It is possible that a pickup coil or ignition coil begins to fail when heated up. or an electrical splice is reacting to heat or vibration.
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Old 10-13-2017, 02:49 PM   #8
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Well, compression is within specs and I was thinking electrical also since the bike has many spliced wires. This bike is driving me! Thanks for the advice
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