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Wasted spark system. If fuel and electrical is all good/correct it is often the case in these symptoms that motor cycle spark plugs that although looking good and firing outside of the engine are breaking down and will not fire under compression pressures on a power stroke but will fire unburned fuel on the unpressurized exhaust stroke when the plug again fires in a wasted spark ignition system and when so firing the result is a backfire, usually quite loud.
BACKFIRE TROUGH EXHAUST IS A VALVE TIMING ISSUE! WHILE ON THE POWER (EXPLOSION) STROKE...EXHAUST VALVE IS OPENING TOO SOON ...WHILE FLAME PATH IS STILL IGNITED, SENDING IT OUT EXHAUST. I WOULD PERFORM A VALVE ADJUSTMENT AT A MINIMUM
Change what you said and check to see if both plugs are getting spark, maybe you have a bad coil. also get a carb rebuild kit. The backfiring is most likely caused by the ACV on the side of the carb. Here is what they look like.
Make sure firing order is correct for the plugs.Also compression test is easy way to make sure valves are working.was it doing this before rebuild carbs.Thank you for your service, I am greatfull for the FREEDOM!!!!
Ok, due to different terminology used by different people, I'm going to assume that by "backfire", you mean it pops through the exhaust system when you back off the throttle. On stock exhaust systems which use the "crossover" connector to connect the front and rear pipes, the backfire is usually caused by an air leak somewhere in the exhaust system.
When you back off on the throttle, the mixture is usually too rich to burn in the exhaust system. But, if you have an air leak allowing the scavenging effect of the system to **** air in, the mixture becomes combustable and is ignited by subsequent exhaust pulses.
Check your exhaust system gaskets and replace them if necessary. This should stop your problem. Rejetting the carb may be necessary as well.
check for leaks around the exhaust headers,mine did what yours is doing,i replaced the copper exhaust seals in the head(exhaust ports),air is getting into your exhaust system and it mixes with the unburnt fuel and ignites causing the backfire,i replaced copper seals(about $2nz each) and problem went away
With the key off and the engine "running down", the idle circuit fuel is still going to into each cylinder then out the exhaust. A hot spot in the exhaust can ignite the unburned fuel creating an explosion, ( backfire ). Let the engine run down to an idle THEN turn the key off.
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