2004 gs500 high idle

[Ksmedicrn]

Hello all- new to the gs500 & new to the forum. I recently bought a 2004 gs500, that has been modded into a cafe racer. So far, I've taken the carbs apart and cleaned them (not terrible, but definitely dirty), and cleaned the gas tank with evapo-rust. Also have new fuel lines and new fuel filter. Since I've resssembled the bike, I keep having a high idle (around 4K rpms) anytime I give it some throttle. Throttle cable isn't sticking as far as I can tell, and I don't think I have a vacuum leak. Wondering if the next step is to balance the carbs, but I don't know how or why this would cause my issue. Has anyone had a similar problem? Also, if there's already a thread on this specific issue please let me know. Thx

[Armandorf]

don't think I have a vacuum leak...check
gas float level...check
valve clearances...check
throttle cable...check
mixture screw ...check

back up the idle adjuster, if set too high will idle high even if everything is OK

[Ksmedicrn]

Checked for a vacuum leak- nothing. Lubed all the cables (throttle, choke and clutch). Took the petcock apart, cleaned and reassembled. Tried messing with the idle screw a bunch, but nothing seems to fix my gas starvation issue- no fuel getting to the carbs (I can tell bc the fuel filter has little-to-no fuel going into it). Should I replace the petcock, or perhaps delete the petcock entirely? Any help would be appreciated.

[Horizon]

Didn't initally sound like you had a starvation problem but if it's dying you can narrow it down by going through the fuel system 1 step at a time.

Have a look where the fuel is getting to in the lines before having trouble.

E.g disconnect the tank pipes from the frame tap and just try see if fuel flows fine from both pipes on the tank, if that's fine see if the frame tap flows fine on prime, if that works try it set to "on" and suck the vacuum pipe and see if that lets fuel through.

If all of those work completely fine I'd try run it on prime, if you still have the issue I'd check the needle, seat and float is set up right. If you don't have any issues on prime I'd try running it with the frame tap set to "on" while sucking the vacuum line yourself to see if the carb just isn't pulling it open.

With all of that you should realstically have the exact place fuel is getting caught up.

I'd maybe wonder if you've closed the idle so far it reduced the vacuum to the frame tap since that's after the butterflies but not sure if that's possible.


Also just to add, I wouldn't reccomend deleting the vacuum tap, it's a safety feature that stops fuel overflowing if you crash or leave the bike at night. It's a simple part and realistically just stops you having a nightmare of a time if you get unlucky.

[Ksmedicrn]

I've replaced all the fuel lines and installed a new inline fuel filter already.

I'd rather not delete the petcock entirely. I think I'm going to get a carb rebuild kit and go back to the beginning. The bike is over 20 yrs old now, and guessing from all the different sized bolts holding on different parts, I think it's been tinkered on by a few different people- lol. If I go through the carbs completely and double check the float heights, new o-rings, etc. I will feel good about that. If the problem still persists, then I'll know it's a petcock problem I suppose.

A separate thought- I read on another post somewhere that a cheap fuel filter can slow down the fuel delivery, since it's a gravity-fed carb system and not pressurized like fuel injection. Have any of you had an issue with a fuel filter between the petcock and the carbs leading to fuel starvation?

[Armandorf]

if you use filters intended for cars or  motorbikes with fuel pump, yes, it will starve.

[Horizon]

It's not uncommon to put fuel filters on so it shouldn't outright cause starving issues, just make your situation simpler and remove it for now, once it's running fine add it back and see how it's doing.

If you're not sure about your filter, you could measure the flow from a tube with the filter and flow from a tube without the filter, time how long it takes to fill 100ml or something and that'll give you a measurement of it's impact on flow.

I caused some issues to my bike by accidently plugging the bowl vent lines, it caused flooding _and_ starving issues so could be worth the 5s it takes to check it's fine.

[Armandorf]

try with the gas cap open, the vent should be working