Backfiring at top speeds...

So my Sachs Sparta backfires at top speed. Am I correct in thinking this is a timimg problem?



Re: Backfiring at top speeds...

by backfire you mean the exhaust is popping?

any misfire can do it..

the exhaust loads up with some unburned fuel .. a successful spark then lights it all off.

Got any clue as to why this started happening? You make any changes lately?

Re: Backfiring at top speeds...

one day I was riding and the rear exhuast bracket fell off. The exhausted bounced around for quite a while before I noticed only connected up at the bottom of the engine. I have a feeling this might have done a lot of damage. Hard to say if the popping started after this as it was pretty soon after I initially got the rhing running.

Re: Backfiring at top speeds...

On all 2-stroke engines, some fresh fuel mixture is wasted ..pushed into the exhaust along with exhaust gases.. It's the nature of the beast.

But this fresh mix usually doesn't ignite in the pipe.. there's not enough oxygen for one reason. It'smixed with lots of inert, burned gases for another. And it needs some sort of igniter for another.

But if there's a leak in the exhaust system, that could supply the needed O2 .. Fresh air enters the pipe through the crack.

Combine that with late ignition timing, or an engine that needs general tuneup, and it could cause backfires.

It makes sense that it's more likely to happen at top RPM where everything in the engine is moving at maximum speed and exhaust is hotter than at any other time. I can picture long, hot flames erupting from the exhaust port at top rpm.

so, i'd check for and repair all cracks or leaks anywhere in the exhaust system and re-check and re-set ignition timing.

Re: Backfiring at top speeds...

Hey I dont think you need to do all of that. If you just look at your timing and make sure it is right you should be fine. If not make sure that your spark plug is gapped right. Finally just clean your exhaust.

Re: Backfiring at top speeds...

the timing appears to be fine. How do you gap a plug? I know this is something that I should have done long ago but never quite understood it. Should a buy a little gapper from the auto parts store? What size should a proper gap be?

Re: Backfiring at top speeds...

The proper gap for the plug is of 18thousenths. if that doesn't work try 20

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