Backfire when throttle closed

[flainn]

This weekend my GZ started backfiring when I let off the throttle. Pop-pop-pop. Never done that before.

Also, it does not seem to want to idle. I had to turn the idle screw way up just to get it to idle properly.

The only thing that I've done to it recently was, I bumped the muffler when I was backing it up. The problems seemed to develop afterward, but it could just be a coincidence.

Any ideas? I'm thinking it's a good time to give 'er a tuneup anyhow.

[Dupo]

How hard did you bump the muffler?

[flainn]

Not hard enough to cause any visible damage, but hard enough for me to be pissed at myself for being such a klutz.

[Easy Rider]

Originally Posted by flainn

This weekend my GZ started backfiring when I let off the throttle. Pop-pop-pop. Never done that before.
Also, it does not seem to want to idle. I had to turn the idle screw way up just to get it to idle properly.

Something has suddenly caused it to run even leaner than normal. The pipe bump may have broken or cracked something in the exhaust system; check for exhaust leaks between the cylinder head and front of the muffler. Also check the back plate of the muffler; might be busted loose.

THEN consider that the muffler bump might be just a coincidence (Murphu WILL get you!!).
A more common cause of what you describe is a leak in the intake side, either the boot between carb and engine or something loose with the air box allowing a leak past the filter.

Last but not least, your idle jet might be plugged. The bump might have jarred a little piece of "crud" loose in the carb.

[dan_]

What about a backfire upon starting.. like every time it starts? I had a slight drop on my bike.. okay I completely dropped it onto the muffler side. It was raining and I was putting it in a trailer, slipped, dropped, ouch. Runs fine but whenever i start it "POP!" Should I be worried? Or just tell the dude when i finally take it in for service?

[flainn]

Originally Posted by Easy Rider

Something has suddenly caused it to run even leaner than normal...

I've been meaning to give it a good going-over since I first got it running. Sounds like this'll give me the kick in the rear I need. Thanks for your advice.

[Easy Rider]

Originally Posted by dan_

Runs fine but whenever i start it "POP!" Should I be worried? Or just tell the dude when i finally take it in for service?

Now that's a new one......on me, at least. :??:
I'd guess small exhaust leak.

Does it do that when restarted hot/warm too ??
Are you using any choke ?? When ridden fairly frequently (every other day or so) in the summer time, mine takes about 1/2 choke and usually fires on about the second revolution.

If that's the only strange thing it's doing, I'd say wait and SHOW the service dude instead of just telling him.

[dan_]

Just when started cold. When cold if I don't give it full choke it wont start. Also if i don't let it run a minute or two before I take it off of full choke it'll stall out.

[Easy Rider]

Originally Posted by dan_

Also if i don't let it run a minute or two before I take it off of full choke it'll stall out.

That part is perfectly normal and is worse if your idle speed is set too low.

If the pop and requirement for full choke only happens when it is "winter" cold, then my guess is that is normal too.

Had mine running for the first time in winter weather last week, just to ride it inside off the trailer from the service shop and it sounded more like 50cc.......and appeared that it would take a good long 5 minutes before it would be running smoothly.

[dan_]

How do I know where my idle should be set? I prolly have it set to low because It kinda has that low thump thump.. but not really ya know?