Fuel air lock?

[Guest]

Good evening,

I have a GS750 motor with VM carbs and I'm suffering with what I describe as a fuel air lock. I have a custom tank with no vacuum attachment like the original, so the vacuum is not used on the carbs. Only number 3 is blocked off for some reason (was like it when I purchased).

The problem is it randomly cuts out due to fuel starvation. The only way to get fuel into the carbs again is to undo the fuel line to the carbs/filter wait for air lock to clear and reconnect before full flow. I've checked the tank breathers and petcock filter, so I'm wondering if it's something to do with the carbs?

Any advise is welcomed, as I'm new to VM carbs.

FYI carbs have been cleaned and it runs great until the air lock. Average millage I get on test runs before I hit this airlock issue is anything from 2-30 miles, so not instant and is random...

Thanks in advance.

Paul

[mrbill5491]

What year model GS750? While we wait on that, are you talking about a vapor lock or fuel starvation of sorts? Check your gas cap, if it is sealing off, then your gas won't flow freely. It has to vent at the cap. Might want to lose the gas filter it can restrict the flow of gas as well. These are gravity fed fuel systems and any restriction to the fuel flow could/can cause problems. One other thing, how were the carbs cleaned? If you just used a carb spray that ain't gonna cut it.

[chuck hahn]

The brass nipples on 2 and 4 are vents...should NOT be capped. 3 was the petcock vac and SHOULD be capped if there isnt any need for it now.

[bwringer]

... Check your gas cap, if it is sealing off, then your gas won't flow freely. It has to vent at the cap.

Exactly what I was thinking. Methinks your kool kustom kroozer tank isn't venting.

[snap1]

Thanks for your responses, it's a 1978 GS. Carbs were cleaned with spray and high pressure air. I don't think they are the issue, just needed to understand the vent/vacume ports, thanks Chuck!

I will try further tests on the tank flow and filter given the general consensus, and post back.

Thanks again!

Paul

[mrbill5491]

Carbs were cleaned with spray and high pressure air.

Thanks again!

Paul

Um no, that is not how to clean carbs. Not saying that is your fuel flow problem, it's just not gonna clean your carbs.

[snap1]

I believe it's sorted, thanks for your advice as there was too too many avenues at the start. Especially not understanding the carbs at the moment.

So the issue was fuel filter, there was just not enough gravity to get the fuel though. Hence random air locks. My tank has a petcock filter in it, do you think this will be good enough or should I seek a different free flow filter?

Mr Bill, I've downloaded the carb cleaning guide from the site. So my next maintenance schedule will see the carbs cleaned properly. But for now the motor runs perfect, until I block the carbs with no inline filter...

[Agemax]

the petcock filter should be good enough on its own. inline filter is not required

[chuck hahn]

IF anyones running an inline fuel filter, you want it so its almost standing vertically near the top of the carbs so it doesnt get an air bubble started like if its at an angle. Picture how an IV drip is always verticle so air doesnt get into your veins...some principal. And be sure its not interfering with the throttle linkage.

[chuck hahn]

Carb rebuild tutorials here on the right side under the section labeled other contributors.

http://members.dslextreme.com/users/bikecliff/

[snap1]

the petcock filter should be good enough on its own. inline filter is not required

Great glad to hear! Thanks for your response.

[snap1]

IF anyones running an inline fuel filter, you want it so its almost standing vertically near the top of the carbs so it doesnt get an air bubble started like if its at an angle. Picture how an IV drip is always verticle so air doesnt get into your veins...some principal. And be sure its not interfering with the throttle linkage.

Makes so much sense now you explain it like that. If I get problems with dirty carbs on just the petcock filter. I will go down this route, with mounts etc.

Thanks