Fuel Leak From Carbs

[ruifrsilva]

My '91 gs500 recently started leaking from the brass nipple next to the mixture screw of the left side carb. I thought it might be a float or needle issue and replaced the needles and reset the float heights. The leak is now much less but still slightly leaking from the same spot.

Here's a picture to show what nipple I am talking about. It's the one right behind the mixture screw. Any ideas on what might cause be causing this?

[cloud2692]

You say that the problem got a bit better when you replaced needles and set float height. Just make sure that the new needle has been properly seated as they can sometimes have issues with this even from new, Ive always sat them in a class of boiling water for a minute or two then placed them in the carbs with a splash of petrol just to ensure that they seat correctly.

Before you go pulling the carbs down again grab a small hammer or end of a screwdriver and just firmly tap the bowl a few times while the bike is running and see if it stops, if it does this could mean that the float needle isnt sliding smoothly.

Good luck,
Mitch

[ruifrsilva]

Thanks, I'll try that out before pulling them again.

Is there anything other than float and needle issues that could cause this? The needles I replaced were a few years old and not OEM. The tips showed some wear, so I was expecting the new needles would have solved the issue.

[mr72]

FYI my '92 doesn't have those nipples on the bottom of the carbs.

Check out this picture from the other thread:


It looks like there's a recessed hole cast into the carb body right where your carbs have those nipples but it's not open to the inside of the carb. Maybe yours are not the stock carbs or some regional difference? Dunno.

Anyway, if it's leaking there you'd have to look at a carb flow diagram and see where the fuel supply is that intersects the orifice at the other end of those nipples, then see if there's an o-ring or something upstream that might be bad. If I had to guess, just because of proximity, I would consider while I had the carbs off to replace the o-rings on the idle mixture needles. Truth is I think those things get set from the factory and don't leak but tinkerers like us take quarter century old motorcycles and start turning that mixture screw all the time and the o-rings are just not intended for that much adjustment pressure so they go bad quickly under this hard use and then leak. I have had them leaking on both sets of carbs that were on my bike.

IMHO I don't think it's likely your float needles leaking, but it could be. Or, I should say, it could be that a tiny leak of the float needles is allowing fuel to flow to this area and then leak past whatever's supposed to keep it from leaking. But the float valve is open part of the time, much of the time while it's running, so even if it's a leaking (closed) float valve that is "causing" this, once the bike is running it'll leak again since the float valve will be open. Point is, something else needs to seal this hole. Or, how about just putting a cap over those nipples? Solve it the brute force method.

[ruifrsilva]

I'm pretty sure my bike is a California emissions model. Those nipples would have originally gone to the charcoal canister. I have since removed the canister as it was all broken up when I bought the bike anyway. Its interesting that the non California emissions carbs don't have those nipples. Maybe you're right and I should plug them up somehow and see if it affects anything.

The mixture screw O-rigns were replaced when I installed the extended mixture screws about two years ago. I will take a look at them if I have to pull these carbs out again to make sure they haven't deteriorated since.

Thanks again for the suggestions!

[mr72]

In that case I'd just put a cap on them and be done with it.