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Interesting intermittent carb over flow issue ...

J

JoeNashville

Forum Apprentice
So I've been riding the 79 850G with new top end and rebuilt carbs Mikuni VM26SS and it runs great.
I'd like some informed ideas about one issue, especially is they're different from mine!

So carbs 3 and 4 overflow occasionally and intermittently, and rarely.

Everything inside is either new or in excellent condition. I've checked repeatedly (and keep checking)

After the last ride I realized it's only after the engine is very warm, after a long ride (which also means the fuel has warmed also) and after riding agressively.

Also, after the engine cools and on the next start they don't leak... back to normal.

It never leaks sitting, either on side stand or center stand, no matter how long it sits, even with petcock on prime. And doesn't leak when I start it and just let it run after normal warm up.

I'm thinking it's somehow caused by warm/hot fuel? But how??

Important fact, I don't have a secondary inline fuel filter which now I'm thinking may be a factor, even though I don't see a need for one because the in tank filter is very good. (AND there is simple so little room in there for one it's a PIA)

Today's test will be to go for a long-ish ride at moderate pace to see if the problem recurs.

Here's what I've got:

1. It's somehow related to warming fuel that's causing an issue... weird right? (welcome to my world)
2. Upon head scratching, now I think it may simply be debris getting into the carb from warming fuel and agressive riding.

If today's test does not cause an overflow (#2) I will put an inline filter on and test that.

Anyway that's a summary of what I've got, any ideas (especially out of the box thinking) would be helpful.
 
Last edited:
What are you riding Joe? Put your bike details in your signature line so we don't have to keep asking...

Top right: My Profile/About Me
 
Where are they leaking from on the carbs?
The overflow?
 
They leaked from the overflow. I replaced the overflow lines with new longer ones to make sure they missed the exhaust and labeled them so I could tell quickly which ones were overflowing.

I went for a ride yesterday morning and there was no overflowing, but it was cool and I just cruised around.

I'll probably go out Monday after work and try to duplicate the problem.
I'd like to point my laser thermometer into the tank so I can track the temp of the fuel. I'm really curious how much the temp of the fuel varies.
 
Sounds like the fuel level in 3 and4 are too high..Ck. fuel level and sync...Tip: clear overflow hose, turn it up next to the side of the bowl and check the actual fuel level..You can watch it in the clear tubing..Fluid seeks it's own level..Get it ?? When heated it expands and there fore overflows..Make sure they are vented to atmosphere properly..
 
JoeNashville said:
They leaked from the overflow. I replaced the overflow lines with new longer ones to make sure they missed the exhaust and labeled them so I could tell quickly which ones were overflowing.

I went for a ride yesterday morning and there was no overflowing, but it was cool and I just cruised around.

I'll probably go out Monday after work and try to duplicate the problem.
I'd like to point my laser thermometer into the tank so I can track the temp of the fuel. I'm really curious how much the temp of the fuel varies.
Click to expand...

I have had to install several heat shields on the fuel tanks and fuel lines,Crankcase vent hoses...mostly on ATVs and race bikes..
 
My first GS1150's had a heat shield under the tank, not a clue if OEM or someone had added it.
 
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