I picked up a 93 GS500E as a starter bike about a month ago.  It makes a popping sound on decel that seems to have been exacerbated by lowering the idle. I took the idle from about 3k when warm to about 1.5k.  The right side plug looks lighter than the left.  I have done the following:

Tank of seafoam-treated gas
Checked valves
Float height check
Vac leak check
Gas cap clean
Carb sync

During the carb sync this morning the bike did something I've noticed it do when cold.  It 'sneezed'.  I could see something flow up into the clear tubing and back out.  It's done this to me before, and I can feel it, but this is the first time i've ever seen it. 

The bike has a K&N lunchbox and a supertrapp slip-on.  Based on the partially-empty bags the previous owner handed me, it's got 40 pilots, 150 mains, and one shim.

Any thoughts?

When it "sneezed" did it do it back through the carbs & air cleaner?

It popped up into the clear tubing of the $5 carb balancer that was connected to the vacuum port.

Quote from: snOhio on October 27, 2012, 12:51:52 PM
It popped up into the clear tubing of the $5 carb balancer that was connected to the vacuum port.

Just once, it was probably a fluke then, if you get regular popping back though the carbs it is possible that it could be caused by intake valves that have too little clearance (too tight)

IIRC they had between .04 and .06 when I checked.

bring that idle down a bit 1200ish warm, i think adidas even went crazy and idles at 800-1000.

check all the hoses and make sure the breather hose for the carb is unobstructed.

Also seafoam is GREAT on a car, but it can cause stutters and weirdness, in a 4+ cylinder configuration not to big of a problem but in a 2 banger it can cause a power gap.

Not crazy - I do idle at 1200-1300.
Although I mat be a little insane about collecting parts 

Hmmm could of sworn if was you, then I dunno someone idles sub 1000, that has to take some insanely well tuned carbs lol!


nm, found it.

http://gstwins.com/gsboard/index.php?topic=51816.0

Seems like it was kyle

The "PAIR" system can cause a bit of backfiring on deceleration, especially if you have aftermarket or "modified" stock mufflers. This is my third Suzuki MC with the PAIR system. If you are not familiar with what it does, it introduces air into the exhaust system post-combustion. The idea is to provide oxygen so that any volatile fumes can be burned off, thereby reducing emissions. I don't know how well it works, I do know there's any number of ways to go about disabling it and in each case the annoying "popping" went away. Our bikes are major polluters, much worse than most cars/trucks, although I imagine the CA versions (equipped with catalytic converters) DO burn a good bit cleaner.

Another thought....you mentioned having a Supertrapp muffler. If it is the type where you can add/remove plates, remove a couple of plates (which would increase back-pressure) and see if it clears up? Good Luck with it!

Quote from: OldTwinzNeverDie on October 28, 2012, 07:34:33 AM
The "PAIR" system can cause a bit of backfiring on deceleration, especially if you have aftermarket or "modified" stock mufflers. This is my third Suzuki MC with the PAIR system. If you are not familiar with what it does, it introduces air into the exhaust system post-combustion. The idea is to provide oxygen so that any volatile fumes can be burned off, thereby reducing emissions. I don't know how well it works, I do know there's any number of ways to go about disabling it and in each case the annoying "popping" went away. Our bikes are major polluters, much worse than most cars/trucks, although I imagine the CA versions (equipped with catalytic converters) DO burn a good bit cleaner.

Another thought....you mentioned having a Supertrapp muffler. If it is the type where you can add/remove plates, remove a couple of plates (which would increase back-pressure) and see if it clears up? Good Luck with it!

On my GSX650F I plugged the hose that sucked the air for the PAIR from the airbox, all deceleration popping went away. I don't think a '93 has PAIR?? 

Quote from: Suzuki Stevo on October 28, 2012, 07:45:10 AM
On my GSX650F I plugged the hose that sucked the air for the PAIR from the airbox, all deceleration popping went away. I don't think a '93 has PAIR?? 

Ah, 93....I tend to forget how long the GS has been around!!!

The first bike I owned after a 10 year absence from riding was a 1998 Suzuki Marauder, a cruiser...I bought it thinking it would force me to ride slower, it did, for about 2 weeks! Point being, it had the PAIR system, as did my 03 DL1000. I disabled both of them by putting a bolt in the end of each hose. On the 07 500F I've removed all of the PAIR plumbing.  I reckon I'm going to hell for all of the increased pollution...my bad.

The supertrapp is a straight through design, not the plate kind.  The exhaust appears to have a mid-pipe between the header Y and the muffler.  The end that connects to the muffler looks to have been hacksawed.  Not sure what's normal here, it's my first bike.   

When I seafoamed, I ran the tank down into reserve before I filled it fully again.  I'm thinking that that there's a minimal amount, if any, still in there.