Suzuki GS500 issue with throttle. need advice.

[nimbus]

Hi everyone, newb here.

I just bought my first bike a few weeks ago, and it was running fine at first but now it's having an issue with the throttle, and I am in need of some advice.

The bike isn't responding well when I give it throttle. It hesitates, and only when its at least half way to full throttle does it respond, at which point the rpms jump from idle to about 4-5k+. It really has trouble with only a little throttle, and it stalls after it finally does engage and revs in the 2-3k range.

What could be causing this?

Also, I recently realized I was making a mistake by putting the petcock in PRI whenever I would park the bike for the night. I did that for about a week until one evening the bike just stalled on me when I put the clutch in on the highway. I had trouble getting it going after that and have since gone through the process of draining the oil, which had gas in it, and putting new oil and filter in. Strangely, there were no visible gas leaks, but obviously gas had gotten down into the engine oil. I also checked the spark plugs, which seemed to be in good condition, but they smelled like gas and the right one was a bit wet.

At this point, I'm wondering if the bike is running rich, and if I'm going to have to really dive into some carb work. That would be kinda over my head but I'm okay with that, I'm just wondering what a good approach would be to assess the situation so that I'm not trying to fix things that aren't broke.

My guess is that the float needle is not set properly now due to continued gas flow while sitting in PRI for a few nights, but I don't really know...

What do y'all think?
Any insight is much appreciated. Thanks guys.

[Val]

Before diving in the carb worths to check everything else before it.

For example look at the gas tank and work your way down. Check all the tubes are properly connected to the petcock.

Check the fuel line that fuel flow free and the line is well connected. Check the air breather tube for debris and check the vacuum line to the carbs. Check your gas cap to see if it's ventilating properly. If not, the tank could be vacuuming fuel upward instead of pushing it to the carbs. Check that you have petcock filter and the petcock filter to see if there is any debris inside, impeding the flow of fuel. Check carefully for vacuum leaks. Then do all the carb cleaning.
____________________
Adrian Monk: Unless I'm wrong, which, you know, I'm not...
Yamaha Fazer FZS 600, MT09, XSR 900

[Rogerborg]

[Val]

[Major Doss]

Carbs off I'm afraid. Strip one at a time. Get the float bowl off (square bit of metal at the bottom, held on with four bits of cheese), carefully unscrew the smaller brass screw, this should be the pilot jet, blow through with carb cleaner. The big plastic toilet cistern device is the float. See how it is connected somewhat to a doofer in the middle? This is the float needle. With the carb upright, manually(carefully) move the float up and down. Does the needle follow the float always, like sits on it, harmoniously getting groovy with gravity? Or is there a moment where it sticks until the float pulls the needle from it's seat? If following float, great. If sticky, you need to clean or renew the needle. It comes out easy once you have pushed out the little pin holding the float to the carb. Check for a ridge across the rubber tip, this is also a sign for renewal.

[nimbus]

Ok, fuel hoses and air hose from tank look good. I'm not really sure how to check if the gas cap is venting right...just blow through it I guess? I tried to get the vacuum hose to the carb off but that thing is not budging. I guess that means the vacuum is working...

I noticed the vacuum damper has a hole in its filter though.

[Val]

[nimbus]

the vacuum damper has what looks like a foam filter in it. there is a little chunk missing from the foam.

The problem is also there when its set to PRI.

Okay, so when I said that the vacuum hose was stuck on there tight I actually meant the fuel hose from the petcock to the carb. Still figuring out what I'm looking at here! That hose was a bit brittle so I'm replacing it. I don't think it's causing the issue though.

What I have done so far is take out the carbs and clean them. The jets were clogged, but overall the carb was mostly clean. After that I started it up but it still couldn't idle. So I don't think its the jets. If its even the carbs at all, I'm guessing its a loose fit on top thats letting air in. The acceleration and deceleration is smooth, it runs fine when on choke, its just that the fuel flow gets cut when it slows down.
Truth be told, I didn't really check the vaccuum system that well before because I didn't really know what I was looking at!
So now I'm going to go through and look for any air leaks.

That diagram is pretty helpful. I don't see the thing labeled 'canister' on my bike though...hmmm

[_Iain_]

[nimbus]

Damn, if every part of these bikes are prone to failure what are we doing riding them??

It's a 2005.

[J.M.]

2005, let's see if my memory serves me correctly.

On the tank you have three pipes. Two with a petcock, and one that's just a pipe. The plain pipe is just a breather. The petcock internally has two tubes, which connect directly to each of the pipes. The petcock has two positions, on & off.

The two pipes connect from the tank to the petcock on the left hand side of the frame, to the left of the battery. This is a vacuum operated petcock with 3 positions. The petcock is connected to the carbs via a vacuum hose.

When the petcock is in the "ON" position, the main fuel line is used. The vacuum is used to allow fuel to pass through. If the vacuum is weak, or part of the vacuum seal in the petcock damaged, you may see less fuel flow, resulting in poor performance. The same is true for "RES" except, obviously, using the reserve line. The vacuum is used to "open" the tap. When the petcock is in the "PRI" position, both fuel lines are used (I think). The vacuum is not used, meaning that the fuel is supplied purely gravity fed.

If you're having an issue with your vacuum, running on PRI with a good amount of fuel in the tank would solve it. If running on PRI doesn't solve it, your problem likely isn't to do with the vacuum.
____________________
2004 R1 & 2018 XSR900

[nimbus]

whoa, yeah that diagram is way different than my model.

hmm, if it's not due to a vacuum issue I wonder what it could be..