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

When you rebuilt the carb did you drill out the plug and service the pilot jet circuit?

Sure did. Adjusting it has no effect.

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.

What did you set the valve clearances too?

Set Pilot screw at 1.5 turns out. I replaced the O-ring, double checked float level. Set intake valves @ .002 and exhaust @ .004

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.

Well, compression is within specs and I was thinking electrical also since the bike has many spliced wires. This bike is driving me:crazy:! Thanks for the advice