MZ/MuZ Riders

My 96 sport has been a trooper throughout its long life with me. It has lately developed a knack for emiting a single loud pop on long deceleration? I pulled the carb and checked for clogged jets, have checked for leaks around the intake and exhaust for damaged or shagged seals, tried backing the air mixture screw in increments, all to no avail. I'm aware of the fact that it is likely a lean mixture issue. Just stumped as to why all of a sudden. Any input from the community is muchly appreciated.

Well folks..first thank you for all your help. Problem turned out to be a rich condition rather than a lean one. I methodically started with the one and a half turn out as per factory recomended settings on the air screw. Make a long one short, the skorp will backfire on rich or lean. Setting has to be spot on. I made some micro milimeter adjustment to get the carburation just right. So finally no more pops and the fuel economy has markedly improved.

Had a similar problem on a bike back in the 80's, turned out the air filter needed cleaning.

My Traveller's stopped doing this since I replaced the air filter last season. It was getting rather frequent.

Thank you guys. I forgot to mention that the filter is almost brand new on it, bought from Graham. If I pull the clutch, say around 3000 RPM instead of waiting for the revs to wind down lower, it keeps it from doing that annoying single pop. Still scraching my head here.

Back in the sixties before rice-burners became the transport of choice over here in the UK and when most self-respecting bikes were Brit singles, this was a perennial problem. The received wisdom then, and I suggest it hasn't changed, is that overrun backfires are almost always caused by exhaust leaks - sometimes impossibly tiny ones.

The theory is that some unburnt fuel vapour invariably escapes from the combustion chamber on overrun, but, because of the absence of oxygen in the exhaust pipe, it can't ignite. Introduce a leak (along with enough oxygen) and you get the mini explosion inside the exhaust we call 'backfiring'.

Now, you can debate this all day and get all bent out of shape over it, but every time I've had a big single start to backfire, I've ALWAYS gone to the exhaust plumbing, carefully remaking each joint in turn, and had the problem resolved as a result.

The Skorp's no exception to this useful rule of thumb and, on the 2 occasions I've had backfiring occur, I've traced the problem to the joint between the downpipe and silencer can. I've always fixed it using aluminium foil and silicone bathroom sealant, which hardens nicely to form an neat and airtight seal.

I have seen occasions where carburation has caused backfiring too - but that's always been where someone with the mechanical sympathies of an alcoholic chimp has had a thorough futzing session with the jetting. I suspect that's not the case here (but then I'm just in a good mood 'cos the sun's shining again.)

Yes I'll say most of the time it is the exhaust and there is nothing to worry about.
Mine pops on the overrun occasionally
and I've noticed a small leak from pipe to exhaust can. So that makes perfect sense. Eric

Linegeist, thank you for the advice. I will be giving the exhaust system another look, this time more thoroughly, and hopefully find the culprit there somewhere. The theory you bring to the table is most intriguing. The pop really scares the unwary, and at the ripe age of fifty three, II feel rather silly going around town startling pedestrians

It stops pedestrians walking out in front of you

My 580 BSA/CCM was wicked for it

I came across this,which sounds like it could be a waste of money-

http://www.ebay.co.uk/itm/180947522830? ... 1438.l2649

Think you're right about the ebay valve...never heard of it....I did happen to think of something though...mine used to po on decel a bit about 3k,all the exhaust was checked and resealed,mixture screw enriched,,,,still did it some..ok Well I had read on a Triumph/Norton forum that they leak oil due to crank pressure, knowing that crankcase brethers are two way I figured to make it one way----out only
when piston is coming down,no problem ...fitted a 1 way brake vacuumvalve from a chrysler I think,and presto one way breather...and popping stopped.....hmmmm Just an observation,but it worked for me