Petcock question

[Chuckster]

If I switch my petcock position to "prime", within a short time my carbs are overflowing with gas. Is this a petcock problem or is it a carb problem? I'm getting ready to remove and rebuild the carbs now anyway, but didn't know what would be causing this problem.

[spyug]

Carbs. In prime mode gas will flow unrestricted to the carbs. When sufficient gas has passed into the carb the floats will move up and engage the float valves which are supposed to restrict gas flow to the jets and passages. A piece of crud can keep this valve open causing the flooding. Wear in the valve can also cause gas to pass.

Carbs should have a thorough cleaning and if this continues you may need to change the float valve assemblies ( they come in some carb kits).

Hope this helps.

Cheers,
Spyug.

[Dave8338]

If the tank is full of fuel...the float valves / seats may not hold back the fuel pressure. Float valves with stiffer springs should cure the problem, or, don't leave it on PRIME for more than a minute... :?

[Chuckster]

Thanks guys :-D

[Steve]

If the tank is full of fuel...the float valves / seats may not hold back the fuel pressure.

I am having a bit of difficulty believing that a couple extra inches of head height is going to provide that much more pressure.
OK, so it might push a marginal situation just over the edge.

Float valves with stiffer springs should cure the problem, ...

How are stiffer springs going to help? They don't close the valves, it's the lifting action of the floats that closes the valves. It is my impression (however mis-guided that might be) that the springs are there only to protect the float valve seats. They do this by minimizing the chatter if the bike hits a bump.

...don't leave it on PRIME for more than a minute... :?

Just have to agree on this one.

.

[Dave8338]

How are stiffer springs going to help? They don't close the valves, it's the lifting action of the floats that closes the valves. It is my impression (however mis-guided that might be) that the springs are there only to protect the float valve seats. They do this by minimizing the chatter if the bike hits a bump.

The original springs in my float valves were so soft, that unless the floats bottomed them out (and I don't think so), they didn't hold the fuel flow, while on prime. The rubber tips were soft and the seats were clean. New float valves (the springs were noticeably stiffer) cured the problem. And if anything...my floats are set a little to the lean side. Just my experience with the situation...may differ with others.

I am having a bit of difficulty believing that a couple extra inches of head height is going to provide that much more pressure.
OK, so it might push a marginal situation just over the edge.

OK...I misread this twice. Kept adding an "L" and mis-spelled it.