SUZUKI GS500F

[JonathanYost]

Was coming home from a roadtrip and stopped to fill up with gas. About 10 miles down the road I heard a weird sound from the engine that was almost like the sound of a spark plug missing. When I came up to the next light my rpm idle was at about 1100 instead of the normal 1500. At the next light I pulled into a coffee shop and when coasting into the parking lot the engine kicked off. Let it sit for a while, and rode home with same low idle. Got into the garage and was still hearing that almost spitting sound and the engine seems to be sputtering a bit. Siphoned the gas out of the tank, replaced the spark plugs...and there is no opening in the local Suzuki shop for me to get it in to be looked at by a pro. My dad fears it may be a blown piston and that noise being the compression. But the noise is only every now and then but the sputtering and low idling is continuing.

Any suggestions????

[Wrider]

I'd put money on it being bad gas or a loose spark plug. Since you just replaced the spark plugs I'd say you had bad gas. Possibly some water in it. We had a batch of that here recently, two bikes came in yesterday with about a 50/50 mix of gas/water.

[JonathanYost]

Well, the spark plugs weren't loose. The engine is still sputtering and running low at idle still. The spitting sound is still happening, but not as bad as before. Guess I will give it a few days and see what happens as that gas gets run out of the system. My mom is using the gas I siphoned out in the lawn mower and it doesn't seem to be having a negative affect on that engine.

[s0crates82]

there are a lot of gs riders at gstwins.com forums that might be able to help.

[JonathanYost]

So the spitting sound is coming from the intake side of the bike. Just to the right (rear) of the spark plug and maybe up a little bit.

I've pretty much ruled out that this is not a case of bad gas as I have put 400 miles on the bike since the spitting/missing sound started and it is not getting any better even with the addition of Seafoam and Heet. I've been told to check for an intake leak by spraying wd40 on the connection hoses from the engine block to the carbs. So, tomorrow that is part of my project. But, all hoses look to be in good condidtion and attached properly.

Also posted this problem at gstwins.com

Gotta say...things like this make me miss my Ninja

[coffee_brake]

WD40 is not the same formula it used to be. It is now less flammable. So I find that WD40 is not good to use to test for an intake leak. It doesn't combust readily, so it doesn't make the idle go up if it finds an intake leak.

I use carb cleaner. It's cheaper, but it WILL eat the paint so I make sure to have a bit of thin cardboard blocking off anything painted when I test for an intake leak.

[JonathanYost]

This didn't seem to fix the problem either. I let it warm up for about 10 minutes and after it stalled out 3 or four times with the choke all the way in I decided that just maybe the bike was fuel starved a bit. So I adjusted the knob that increases/decreases your idle speed and got the idle back up to around 1400 with the choke all the way off. The bike didn't spit or sputter anymore the entire time I had it running.

SO...I turned the bike off for about 10 minutes, let it cool down and the restarted it. As soon as I put it in gear and pulled it back into the garage it made that spitting sound again.

But, at least I have the idle speed back up to where I won't be stalling out at lights and stopsigns anymore. I'm not sure if a dirty fuel filter would be causing all of this either. I have to remove the gas tank to get to the filter, something I'm not really looking forward to though everyone says how easy it is to do.

[mydlyfkryzis]

Sounds like a vacuum leak.

Check the carburetor boots, vacuum lines, line to the fuel petcock if you have a vacuum operated valve.

[JonathanYost]

did all that today, not a single leak anywhere.

found one article that described a dirty fuel filter that would cause a spuratic engine missfire...which is what is happening. The GS500 has an odd filter that is actually connected to the bottom of the tank in between the tank and the gas lines running to the on/prime/resevoir petcock.

gonna have to troubeshoot that one at a later time though. for now the spitting and sputtering is only happening when the bike is cold, and just for a second or two. But once warm it's ok now that I've opened up the idle valve a little bit. Something is starving it of gas, thats for sure.

[mydlyfkryzis]

If it is a hissing sound, and your vacuum hoses are o.k., maybe it's the fuel tank vent?

When it starts running odd, open the fuel filler cap and see if the problem goes away.