Petcock failure gas pushing through carb - Kawasaki Vulcan Forum : Vulcan Forums
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post #1 of 24 (permalink) Old 04-13-2018, 02:21 PM Thread Starter
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Petcock failure gas pushing through carb

Just did a bunch of carb and petcock work. After 20 minutes running like a champ bike died and gas is rushing out carb. Pulled the line off the petcock and gas is flowing freely. Question is, shouldn’t the carb be stopping it? What’s the difference between a failed vacuum petcock and a cheap open/closed one in the open position?

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post #2 of 24 (permalink) Old 04-13-2018, 02:41 PM
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If the petcock is allowing fuel to free-flow then yes, the carb will get overwhelmed. Remember that the entire weight of all the fuel above the carb will be pushing downward in such a scenario.

I doubt there is any difference in a failed petcock and a cheap one in the open position. Flow is flow.

I think what has been proved here is that the flow of fuel from a properly vacuum operated petcock is less than that flow coming from a failed/fully flowing petcock. The carb can handle whatever amount the vacuum fed flow is but not a gravity full flow is. Then again, I'm just guessing it died (stopped running) due to too much gas. Regardless, once it died (therefore stopping the vacuum) and the fuel continued flowing, the carb got flooded in a real sense.

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post #3 of 24 (permalink) Old 04-13-2018, 03:22 PM
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True but when the engine is running the the vacuum operated petcock is open the full amount of gas in the tank is pushing on the float and needle.
The fact that the float did not stop the gas flow means you have something lodged in there keeping the float from stopping the gas and flooding the carb.
OR the needle for whatever reason is not sealing as it should.
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post #4 of 24 (permalink) Old 04-13-2018, 03:55 PM
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Ok that makes sense. I didn't know if the vacuum was enough to COMPLETELY open it or varied during the run time. Yeah, I can live with that reply.

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post #5 of 24 (permalink) Old 04-13-2018, 04:41 PM
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Haven't had a bike for many years until a couple weeks ago. My 800 had a bad needle and bowl gasket. Mine was leaking too, but the petcock is good. Replaced the needle, float, and bowl gasket. If the needle and bowl gasket is good it shouldn't leak. We had full tanks of gas against the float and needle years ago and they didn't leak. My needle had a ring around it, and the gasket was flat when I took it apart. Don't know what they cost though as the dealer paid for them, I just bought the bike.
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post #6 of 24 (permalink) Old 04-13-2018, 04:42 PM Thread Starter
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Yes im an idiot. I completely forgot that fuel coming through the carb was a float issue. The friend that came to pick me up gave the carb a little tap tap taparoo and she closed. Got her home and looked over again. With the needle seated the flow through the petcock was much less but still decent. Would the float being stuck open without the engine running create vacuum, opening the petcock more?

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post #7 of 24 (permalink) Old 04-13-2018, 04:46 PM
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Quote:
Originally Posted by Fastboat View Post
Yes im an idiot. I completely forgot that fuel coming through the carb was a float issue. The friend that came to pick me up gave the carb a little tap tap taparoo and she closed. Got her home and looked over again. With the needle seated the flow through the petcock was much less but still decent. Would the float being stuck open without the engine running create vacuum, opening the petcock more?
The petcock should NOT allow gas to flow in the on or reserve position. You probably have two problems.
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post #8 of 24 (permalink) Old 04-15-2018, 10:25 AM Thread Starter
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Drained a little gas out the bottom of the carb, looked clean. Have her another good run and all seems good. The petcock rebuild was definitely a failure, there is always a little flow. Has anyone added an inline fuel filter? I guess there is one in the tank but thought it might not be a bad idea.

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post #9 of 24 (permalink) Old 04-15-2018, 12:10 PM
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Rebuilds of fuel tap have a poor success rate.
Replacements always work.
If your fuel tap dribbles when it shouldn't, it will fill your crankcase with gas.
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post #10 of 24 (permalink) Old 04-16-2018, 11:31 AM
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If fuel leaks thru in ON and RES, replace petcock w/OEM new. If your hose is not OEM but rather some rubber hose the PO got at a parts house, buy an OEM one. They are molded correctly for fit and flow and made of a compatible rubber like neoprene which ethanol will not degrade. Do not put a valve or a filter in the fuel line. Both restrict/plug/etc. I've seen many bikes with a rubber hose that is degraded on the inside, a little fuel valve and a little filter. All three contribute to problems down the road. Tiny flecks of rubber in the float valve and jets really suck! Fix it right if you are going to ride it. I agree with sfair and gas finds its way into places you don't want it, including rear cylinders. And rebuild kits for petcocks are hit and miss.

NOTE: If your carb is overflowing it is either from an obstruction in your float valve (like a tiny piece of degraded rubber) or your float is bent (or assembled wrong) and is hitting on something inside the carb. In both cases tapping on the carb can temporarily fix either.

Fix it right. You will be time and money ahead in the long run. Your bike is 18 years old and when we ride older bikes, some components just have to be replaced with new. Keep us posted!

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