2004 VULCAN PETCOCK CONFUSION - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
From the gas tank to the carbs
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post #1 of 9 (permalink) Old 02-23-2018, 10:45 AM Thread Starter
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Thumbs down 2004 VULCAN PETCOCK CONFUSION

I'm so glad I found this site. I have a problem with the new bike I have. It is a conversion to a bobber so no air filters on each carb just a breather vent k&n. I discovered allot of rust in the tank and had to acid it and rinse thoroughly. I also had to put a new petcock valve, I dont know if the old one was modified to bypass the diafram. Now I replaced all the lines and put new filers in line. I am getting no fuel to the carbs!! I have found that both carbs where the vacuum lines come out were plugged so I put a new line on both carbs with a "T" fitting. The other "T" coming off of the carbs middle joiner I put on the sending unit vent. I have fired it allot with starter fluid and never got any pull on the petcock to fill the lines. Help please, ty in advance JD
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post #2 of 9 (permalink) Old 02-23-2018, 12:25 PM
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Hi, couple of things.

Adding filters to the fuel line may result in gas trying to run uphill which it will not do. Fuel lines should be downhill all the way.

Carbs have three connections that look somewhat alike. Fuel in, Vacuum out and float bowl vent, mixing them up gives very unsatisfactory results. Your problem description confused me as to which pipes you have where.

Typically the petcock to carb vacuum line is from the left hand carb only, it is the shortest route for the pipe. If the bike is coastered or marbled right hand vacuum is capped, if not it runs to a valve under the tank.

Both bowl vents are teed together and the long part of the t placed where no significant pressure or vacuum is applied, tucked up under the tank is a good place.

Is the new petcock the standard Vulcan one with three connections, Fuel out either side and the vacuum in the middle? Test it by sucking on the vacuum port and fuel should flow? Or the Yamaha manual operated with no vacuum connection?

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post #3 of 9 (permalink) Old 02-23-2018, 12:47 PM
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Get a Yamaha TW200 petcock and problem solved.
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post #4 of 9 (permalink) Old 02-23-2018, 01:36 PM
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everything above +1.

the stock petcock has 3 hoses from it, 2 for fuel, one (center) goes to the vacuum port on left carb (line is only a few inches long). if I recall, putting a T in the vacuum ports from both carbs and sending it to the petcock resulted in unreliable results, but my swiss cheese memory may be failing me there.

Also, you will want to run some sort of air filters on the carbs, leaving them open will result in weird operating characteristics due to turbulent air entering the carbs. the filters do more than filter, they also smooth out the air flow

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post #5 of 9 (permalink) Old 02-23-2018, 01:49 PM
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Apply vacuum to the petcock vac port and test the petcock. New isn't always good.

Run only one vacuum hose to the petcock.

Filters can sometimes not allow enough fuel flow, since there'e only gravity feed and no pump pressure.

Quote:
Originally Posted by michiganteddybear View Post
everything above +1.

the stock petcock has 3 hoses from it, 2 for fuel, one (center) goes to the vacuum port on left carb (line is only a few inches long). if I recall, putting a T in the vacuum ports from both carbs and sending it to the petcock resulted in unreliable results, but my swiss cheese memory may be failing me there.

Also, you will want to run some sort of air filters on the carbs, leaving them open will result in weird operating characteristics due to turbulent air entering the carbs. the filters do more than filter, they also smooth out the air flow
That's my thinking also. A tee in the vac line, at cranking rpm, probably behaves like a vacuum leak. One carb will be trying to pull vacuum through the other and also the petcock, possibly not allowing the petcock to open or stay open.

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post #6 of 9 (permalink) Old 02-26-2018, 03:37 PM Thread Starter
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I removed the "T" and then hooked up a vacuum pump. One carb was dripping fuel and the other was dry in the filter and the carb. New filters and New fuel line.
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post #7 of 9 (permalink) Old 02-26-2018, 07:03 PM
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Quote:
Originally Posted by JD Bryan View Post
I removed the "T" and then hooked up a vacuum pump. One carb was dripping fuel and the other was dry in the filter and the carb. New filters and New fuel line.
Sounds like a stuck float on the leaky carb, depending where the fuel was coming from.

On the other side, maybe the one port on the petcock is clogged with rust/debris? Take it apart, check/clean? That's the only reason I can think of for one side flowing and the other being dry.
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post #8 of 9 (permalink) Old 02-27-2018, 03:32 PM Thread Starter
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Red face The conclusion

I did re-check the NEW valve using a vacuum pump and the gas shot right out it. I didn't want to take the carbs apart so I just shot a quick burst of compressed air down the carb that was not getting fuel and the third burst opened up the carb. Hooked up all the lines again and started right up! I did keep the filters in the fuel lines. Thanks for all the help~!
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post #9 of 9 (permalink) Old 02-27-2018, 03:53 PM
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Sounds like something stuck the float and now you have it un-stuck. Nicely done! Might not be a bad idea to flush the carbs at some point or to add a bit of in-tank cleaner like Seafoam or B-12

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