Backfiring and no power

[Director59]

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

[derbydave]

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

[Director59]

Sure did. Adjusting it has no effect.

[derbydave]

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.

[derbydave]

What did you set the valve clearances too?

[Director59]

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

[derbydave]

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.

[Director59]

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