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JR80 pops & backfires

Joined
Feb 25, 2001
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#1
I've got a suzuki JR80 that I use for cruising around my property as a pit bike. It recently started to pop and backfire randomly and now it is physically not ride able because of the popping.

The bike still starts up first kick and will idle but as soon as you twist the throttle it will pop/miss and then backfire out the exhaust. Once it backfires it usually stalls the engine.

From research online I've heard that most of the time when a 2-stroke does this its a sheared key on the ignition. I popped off the ignition cover and all looks to be well in there. No metal shavings and I can still see the key intact.

Could it be a bad coil? Want some guidance here before I start buying parts. And no I haven't checked the compression yet. The top end has less then 5 hours on it.
 
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Feb 25, 2001
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#3
I took the oil injector system off years ago. But haven't checked the fuel! I should though...

I did change the spark plug & dropped the fuel bowl to clean it out.
 
- a d v e r t i s e m e n t -

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Feb 25, 2001
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#6
Okiewan - The gas is roughly 2-3 months old. Non ethanol 91 octane and castor 927 @ 40:1.

Jaguar- You are correct. I guess I will dig a little bit further.
 
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Feb 25, 2001
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#8
Update:
Tore down engine for top end rebuild. Sent the cylinder to local motorcycle machine shop
They bored the engine I think it was 10 thousands over and supplied me with correct size piston/rings.

Installed piston/rings new gaskets and assembled. Still experiencing same issue! I thought it could be broken reeds so I tore the motor back down (unfortunate design, reeds are on the underside of jug) And put new boysen reeds & new gaskets again. Start engine up and same issue.
 
- a d v e r t i s e m e n t -

Joined
Feb 25, 2001
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#9
I'm thinking of putting in new base gasket as I re-used that paper gasket the last time I put it back together. New headgasket each time I tore it apart. If the backfiring doesn't stall the motor it will start to run with a higher idle almost like it's running away. I'm sure that's a sign of an air leak. But could an air leak also cause it to backfire out the silencer and airbox?