float needles should be the same shouldn't they - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 14 (permalink) Old 09-12-2016, 07:01 PM Thread Starter
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Petcock cause this issue?

I've been having an issue with hydrolocking. Suspected the floats because I figured if the floats would cut off the carbs would overflow OUT the side of the carbs. Instead it overflows into the cylinders and hydrolock and causes hot start issues.

Figured out tonight the petcock isn't shutting off, found the oring to be bad on the vac system. Gotta try and find one tomorrow.

So just looking for others opinion on that being the only cause of the fuel hydrolock knowing for certain the petcock isn't shutting off.

Side question that is just as important...... Does the petcock adjust it's flow based on how much throttle it is getting, creating more vacuum? So if it were locked open and not shutting it would run richer?


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Last edited by One1; 09-12-2016 at 08:05 PM.
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post #2 of 14 (permalink) Old 09-12-2016, 08:57 PM
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Length and method of attachment to the float is what counts, as long as the needle valve fits into the hole loosely.

Different length would change where float height should be. Which could be a problem if the needle valve is too long. Too short would not allow the tip to seal the inlet.

The tip is all that seals the inlet, size of the body won't matter as long as it fits into the hole.

Very good chance they are the same.
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post #3 of 14 (permalink) Old 09-12-2016, 09:44 PM Thread Starter
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Thanks, what about the rest. Any opinions....


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post #4 of 14 (permalink) Old 09-12-2016, 10:16 PM
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A bad petcock that passes fuel acts no differently from a standard one set to "On". That alone won't flood. While jets control fuel flow, it's also affected by fuel pressure which is regulated by the floats. That's one reasons float bowls exist on carbs rather than just filling all the way.

Make sure the valves are sealing. Blow air through the inlet with your mouth as you tilt the body. It should gradually stop the air flow completely no matter how hard you blow. Compressed air might just blow through anyway.

If they seal, verify your float levels using tubing on the drains. Factory spec is in the manual which you can download for free: http://www.tocmanufacturing.com/File...nd%20Parts.pdf

Yes, overfilled bowls can leak into the cylinders because that's usually the first place the gas has a place to exit the carbs when the level is forced all the way up to those passages you see behind the filters. If you get enough into the cylinders, which it sounds like you have if you were actually hydrolocking, then you will need to change your oil unless you don't care about having rod and main bearings.
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post #5 of 14 (permalink) Old 09-12-2016, 10:29 PM
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Lol, this is no longer the same post I responded to.

I should add, diameter of the needle is important, because the tip needs to stay centered with the seat. But exact size does not matter as much.

The petcock just opens or closes, no variation.

I'm pretty sure the o-ring only seals the 'handle' ... the knob you use to turn it on-off-reserve, or 'pri'. ... seals that part against the petcock body so no fuel can leak to the outside. Have only done this petcock once, so I may have forgotten if there's more than one o-ring.

Had you checked to see if the vac line is dry just after running? There's a couple of these posts running right now.

Need to look at the diaphragm really close for holes/cracks or even just worn looking spots in the rubber, hold it up to light and try to look through it.
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post #6 of 14 (permalink) Old 09-12-2016, 10:34 PM
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Quote:
Originally Posted by Hexadecimus View Post
A bad petcock that passes fuel acts no differently from a standard one set to "On". That alone won't flood. .
Unless fuel is flowing through the vacuum line, which dumps fuel into the throat of the front carb, which slopes toward the cylinder and gas can just run through if the intake valves are open, or a soon as the valves open.

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post #7 of 14 (permalink) Old 09-13-2016, 12:51 AM
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Quote:
Originally Posted by Spockster View Post
Unless fuel is flowing through the vacuum line, which dumps fuel into the throat of the front carb, which slopes toward the cylinder and gas can just run through if the intake valves are open, or a soon as the valves open.
Yeah, I should have been more specific. A petcock which passes fuel through the outlets, as opposed to bypassing it through another port

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post #8 of 14 (permalink) Old 09-13-2016, 07:27 AM Thread Starter
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When I rebuilt the carbs the other night I did all the proper checks, including setting the floats by turning and blowing the tubes, and they checked out ok. I'm guessing the gas is acting as a micropenetrant and getting by a flaw in the float needles. I know however that I've had several bikes with issues relating to the petcock not shutting off and the overflow out the carb throat has flooded the cylinders before so that's why I was curious about that. I've visually verified the oring on the petcock vacuum rod is defective. See pic below, it got pinched and is missing a chunk so it isn't sealing and shutting off. If you shut the bike off and open the fuel bowls on BOTH CARBS they will run forever until the tank is dry unless you manually shut the fuel off.

I need to know if the petcock vacuum regulates a particular CFM based on vacuum or is open fully when the bike is running. I suspect it's wide open and leaves the carb up to fuel regulation, but I don't want to guess. It'll matter what size oring I go back with.

I shut the petcock off manually and the cylinders do NOT flood so I believe this is my first and primary issue. The overflow on these carbs seems to be internal on the carb? If so it would leak through the carb and drain back into the cylinders.



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post #9 of 14 (permalink) Old 09-13-2016, 07:34 AM Thread Starter
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Quote:
Originally Posted by Spockster View Post

I'm pretty sure the o-ring only seals the 'handle' ... the knob you use to turn it on-off-reserve, or 'pri'. ... seals that part against the petcock body so no fuel can leak to the outside. Have only done this petcock once, so I may have forgotten if there's more than one o-ring.
You're thinking of the large oring regulating the main between off, res, and on. I'm talking about the one pictured above that regulates fuel based on vacuum which I suspect opens more with more vacuum (throttle) based on the diaphragm and spring that is like the one on the side of the carb. That would explain some issues with richness under certain conditions if it is wide open with a bad ring. While the floats are regulating this, the overflow feedback is adding to the issue and bypassing the floats.


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2005 Vulcan VN750 (silver)
(2) 1994 Vulcan VN750 (red)

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Last edited by One1; 09-13-2016 at 07:37 AM.
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post #10 of 14 (permalink) Old 09-13-2016, 10:18 AM
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Ok, the o-ring in question is on the metal center plunger?

It takes a small amount of vacuum to open the petcock, and I don't believe there's any variation according to throttle position. Regardless, the needle valve should be capable of stopping the fuel flow when the bowl is full.

Hard decel produces the highest vacuum, if the flow was proportional to vacuum, it would be giving the most fuel when it's least needed.

Float height too high would cause overfilling of the bowl, as would a sticking or leaking needle valve.
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