MZ/MuZ Riders

Picked up a new Ron Woods low pipe MZ 500 glasspack muffler, and installed it, pic attached. Lots more grunt, no stumbling, idles well at ~1200 RPM, and lot more noise which I kind of expected. I still have the stock Bing carb, and am getting afterfire/popping on deceleration through the new muffler. I was not getting it with the ultra-quiet stock A2 can. Or maybe it was muffled out and I just couldn't hear it. I had rebuilt the stock Bing CV carb and replaced all the o-rings and diaphragm. I moved the needle back from the #4 to the #3 stock position (lowering it), didn't help with the backfiring. I've researched and have read that this is usually caused by a lean condition, and that the pilot (idle) jet needs to be larger for this problem. All jetting at present on the Bing is stock, and the engine (9000 km on it) runs great in all respects except for the popping thru the can when on decel. I have checked for intake and exhaust leaks also and all appears well.

Also, I've never checked the valve adjustment since I've had the bike. Could this also be causing the backfire? I know it's hard to diagnose via email as the possible causes are numerous, but I'd sure appreciate some advice as to where to start. Thanks; Don

Far more likely to be a leaking joint at the silencer or as I once had on my Skorpion a disturbed exhaust seal.

Old Dog

free'r flowing pipe will pop and backfire,
especially on decelleration. its a fact of life, no amount of jetting is going to stop it,
and to be fair why would you want to, it sounds awesome

Judging from how blue the headpipe is in the photo, I'd say it's probably quite lean. Less restriction - more flow - jet up. I'd raise the needle and go 10% larger on the idle jet for starters, increase the main jet size if needed.

i have had the bing carb on bikes since 1972
it works good is reliable
and the carb i love to hate hate
had a r90s for 28 years had delortho carb
never laid a tool to them other than drain crud out of them
nuff said dave

Thanks for the responses. As far as leaks on the head pipe or at the can, I can find none testing with a flame. It doesn't even flicker. Also did the WD40 spray test around the carb intake and the idle remains steady. The blue pipes were like this when I got them, but it still could be running lean, and I think it is, even though the plug looks good. I called Bing and they recommended a larger needle jet first, then raise the needle one notch second, then a larger idle jet if needed, doing one change at a time. And while I'm awaiting for the parts I'd better check the valve adjustment. -Don

I have the same thing with mine. There is a bigger main jet installed to match the pipe. I agree with HMMNZ that the sound is awesome! I have blown out a couple of the end caps over the years, but it can be replaced. They were aluminum, but now steel.

FIXED! The larger needle jet (2.68) and idle jet (48), then readjusting the mixture screw a bit richer cured it. I still have slight popping sounds when coasting down a steep grade in 3rd gear that sound good, but no more of the ear splitting afterfire bangs like before. Thanks for all the advice on this, especially MZCountryRider who was spot on.

Glad you got it fixed!

Hello
I'm working on the bing carb on my 500 country, stock exhaust but I still think its too lean.
What main jet do you have?
thanks
Larry

vme250 wrote:Hello
I'm working on the bing carb on my 500 country, stock exhaust but I still think its too lean.
What main jet do you have? thanks Larry

I use the 130 main jet, one step up from the stock 125. HTH.

For what it's worth, I put a less restricive exhaust on my Country (kind of a homemade deal). I assumed it would need a bigger main jet so I put in a 130, it ran like crap! Put the stock 123 in and it runs fine now. I'm thinking that CV carb diaphragm compensates for the changed flow??
This bike still has way less power than other 500 singles I've ridden...