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Petcock is confusing me, please help.

  • Thread starter Thread starter sark
  • Start date Start date
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sark

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Hello everyone! I've read everything I can about the petcock on my 450. I assume it is a vacuum petcock? Well anyway here is the prob. I run the bike for 10 min or so, other than some major lean-ness (pods/exhaust) it seems to run alright with no flooding. Then I let the bike sit for a couple days and my left filter fills up with gas, major flooding. These has happened twice in a row so far. Im confused about how it is flooding when it isnt running. Is the petcock still supplying fuel to the carbs???? Could it be a float/float valve problem? `And it's only on the left carb. ANy input is appreciated!
Thanks
 
sark said:
Hello everyone! I've read everything I can about the petcock on my 450. I assume it is a vacuum petcock? Well anyway here is the prob. I run the bike for 10 min or so, other than some major lean-ness (pods/exhaust) it seems to run alright with no flooding. Then I let the bike sit for a couple days and my left filter fills up with gas, major flooding. These has happened twice in a row so far. Im confused about how it is flooding when it isnt running. Is the petcock still supplying fuel to the carbs???? Could it be a float/float valve problem? `And it's only on the left carb. ANy input is appreciated!
Thanks
Click to expand...

Left carb = sidestand. The petcock works on a vacumn when it's working as it should. Also assuming you have it in the "ON" position.

When it's in the "PRI" position the fuel just flows out by gravity, like opening a faucet. They also do this sometimes when they fail.........

Sound like it's time for a new one. Have you rebuilt/dipped your carbys ? The needle valve seats SHOULD keep this from happening, but if they're old and shrunken they probably won't.:)
 
If it's the factory petcock, it is leaking gasoline into the carbs. The carbs should just fill up, then the float shutoff valves should seal and stop any further flow of gasoline. Evidently at least one of your shutoffs isn't fully seating. That's pretty common.

I would get a new petcock. If it's leaking, you can't trust it to properly function when you want it to pass fuel either. Plus, it could start leaking into your vacuum tube and into a carb, which produces lots of pretty smoke out your tailpipe.

I know this one from personal experience.....
 
And if you play around trying to ride it regardless of the problem, you'll fill your crankcase with gas.

Ask me how i know :(

Locate and correct the problem.
 
Thanks fellas, I'll get to ordering one today. But in the mean-time, can I disconnect the vac line from the petcock and run it on prime? Someone told me that may work, but I'm pretty confused by the operation of this seemingly simple device. Haha...
 
sark said:
Thanks fellas, I'll get to ordering one today. But in the mean-time, can I disconnect the vac line from the petcock and run it on prime? Someone told me that may work, but I'm pretty confused by the operation of this seemingly simple device. Haha...
Click to expand...

You can, but you'll have to plug the vacuum hole on your carb.

Plus, if the petcock is leaking through the fuel line and not the vacuum line, you'll still be overfilling your carbs and flooding the filter.
 
Last edited:
For what its worth, with the carbs completely disconnected from the bike, the petcock allows fuel through on the "prime" setting and no fuel through when set to "on."
 
Ok one more diagnostic. I put the petcock on "on" and applied suction to the vacuum outlet of the petcock (via a syringe) and gas came squirting out of the fuel outlet. Does this mean anything?
 
sark said:
Ok one more diagnostic. I put the petcock on "on" and applied suction to the vacuum outlet of the petcock (via a syringe) and gas came squirting out of the fuel outlet. Does this mean anything?
Click to expand...

sounds like the petcock may be working somewhat...
 
This darn bike is driving me crazy! It must be the float valve assembly then. I ordered a new needle but of course it wasnt the right size... Whats confusing me is how it can be flooding out so badly when it isnt even running. Just to make sure, the choke is engaged when the lever is pushed down, right?
 
It does sound like it's working correctly, at least some of the time. It may be leaking either just a small amount that is only noticeable over the span of hours, not minutes, or the seal may seat correctly some of the time, but not others.

In any event, replace it, you'll know it's good to go then.
 
Just so you aren't confused. You have 2 problems, For the carb to overfill, with the engine off, The petcock & the needle & seat must be leaking. If either one were working properly, this wouldn't happen. Just my opinion
 
I agree with "if either one were working properly it should not happen" as well.

Here is an other thought.

How about the tank? Has it been coated/restored?

Depending on the condition it can be an "uphill battle" with leaks due to debris. One can clean the carbs, install new float valves and seats, rebuild/buy a new petcock, swear up and down that these have been ruled out, and 5 minutes later still have leaks.

In some cases the debris can be washed out while checking things, and become a hidden factor. Only till the next bit of debris gets caught up in the petcock valve seat or float seat.
 
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