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Re: Backfiring when starting
Normally when giving it a bit too much gas. I'm thinking it's timing related and have had a small mess around with it before. I've elongated the hole in the locking tab on the stator and advanced the timing slightly (roughly 1mm of rotation) this seemed to give me a little more top end but hasn't got rid of this anomoly.
Compared to other 2 strokes I've ridden it refuses to start when given a wristful of throttle preferring to be started like a 4 stroke with little to no gas. It idles and runs perfectly so I don't think it's down to jetting, which is set to the recommended UK spec anyway - #7 slide, N1EF needle on 3rd clip, 40 pilot and 180 main. Plug always looks fine on removal.
Should I give it a whirl trying it retarded from stock?,Most 2T's will occasionally give out a SPOOOT sound when kicking over, and then fire on the next kick. If its continous its definately carburation or timing. Do you have or use the ignition map switch ? Try starting it from cold in the 'wet' setting which I think retards the timing a bit. Retarding the timing further will make it even softer power wise.
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The clunking is probably just the kick back from the motor. You're hearing the compensator assembly doing what it's supposed to do.. Which is saving your crank. The whoosh sound ?? could it have been a backfiring while you were trying to start it? Once you ad stabil to the fuel and it gets in the system it will run terrible until the stabil is completely run out of the system. If you're wearing the battery down trying to start it, it will cause the kick back and backfiring through the carb too. Make sure you have your battery fully charged before trying it again.
Exhaust leaks near the exhaust port can draw air into pipe on deceleration and detonate any unburnt fuel leaving engine, causing backfire and high temps.
An overly lean fuel mixture on the engine can make decel backfire worse too.
This is not the news you probably want to hear but backfiring thru the carbs when you have good spark can be one of 2 things... either the valves are sticking / not closing properly due to carbon or the cam timing has shifted from the original position.
It would be best to do a compression test. You should have a minimum of 100 PSIG for an engine with major problems and up to 150 for a healthy engine. If you can not get 100 PSIG then it will be time for some serious engine service.
There is a possibility of the kill switch wire in the handle bar grip grounding under the grip to the handlebar but, since you said you have killer spark I doubt this is your problem.
By misfire, I assume you mean that it is backfiring.
Backfiring typically is caused by an air leak in the exhaust sytem allowing oxygen into the exhaust which will mix with unburnt fuel and can cause a small explosion in the exhuast system - ignited by hot carbon deposits inside the pipe.
Again - this is a likely possibility but not the only possibility. Check your exhaust system for leaks.