Petcock flow rate?

[Jimboslice]

Hello all! Long time reader first time poster so here goes nothing. I have a 1982 cb750k with a petcock that seams to trickle fuel when in the on or in res position starving my baby at very inconvinient times. I tryed ultrasonic cleaning with no luck. Is there anyone who knows if there is an aftermarket petcock that wont destroy my beer funds available? Any temporary solutions so i can ride for wats left of the season and save for a permenent repair? Any advice at all is greatly appreciated!

[TOOLS1]

The petcock does not flow much more then a trickle. These engines do not require a massive flow rate of fuel. If you figure a conservative number of 25 mpg and an average speed of 50 mph, this would mean that your petcock would need to flow 1 gal in 30 minutes to keep up with the engines needs. How long does it take your petcock to drain a gallon of gas? If the bike does start to starve for fuel, you might have a plugged gas cap vent.
What makes you think it is a fuel problem? Ignitions can cause a problem like this on these bikes.
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[Jimboslice]

I beleive it is fuel do to lack of fuel in the bowls, as well as a visual inspection via an inline filter. I did remove the vacume assist when i re built the carbs( those checked out ok on a bench test) i havent done a timing inspection but did check spark and compression and both those are strong.  
The bike would idle ok upon startup but would soon not be able to idle. I belive it is starving itself of fuel. Any chance the s.o.s needs to be put back on?

[TOOLS1]

How did you remove the vacuum "assist"? The vacuum "assist" is not any sort of "assist". The vacuum is what turns the fuel on. When the engine starts vacuum is created. This vacuum then pulls on a diaphragm that opens the petcock. In order to remove this function, you must replace the petcock with one that is not vacuum controlled. Is this what you did to remove the vacuum "assist"? Have you tried running with the petcock on "prim"?
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[Jimboslice]

The petcock on my bike does not have a vacume port. its just the standard on off res. Forgive me if i dont know the name of the part. I see it often refured to as the spawn of satan? And is often bypassed. Its the part that attatches to the carb bodys with a vacume line to the #2 carb. it cuts fuel to the bike when the engine isnt running.

[TOOLS1]

Yea, the vacuum operated petcock is referred to as the SOS. They work great until they do not work any more. I have seen them go bad and let gas be sucked into the engine through the vacuum line. I seen one bike where it had washed the No#2 cylinder down so bad that it needed rebuilt. I have gotten to the point where I do not even try to rebuild petcocks, I just replace them.
What petcock did you replace yours with?
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[Jimboslice]

I didn't replace it. perhaps the p/o did. the petcock flows without the motor running and there is no nipple for a vacuum line on it.

 

this is the part im referring to just so we can be on the same page
ill take a few photos of the petcock when I get home from work and post them. and thank you for the responses.

[TOOLS1]

I have not worked on any that had the separate valve. All the ones I have worked on were built into the petcock. On the parts fich they show two different petcocks for your year bike. If the petcock is just an on/off switch in itself it should be able to flow enough fuel for the bike (it did when it was installed). Is the screen plugged up?
http://www.partzilla.com/parts/search/Honda/Motorcycle/1982/CB750K+A/FUEL+TANK/parts.html
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[Jimboslice]

there was no screen on it, so someone was definitely in the tank before. it does have a build up of crud in the pickup. perhaps ill let it go a few rounds in the ultra sonic tank and clean the gas tank out while I'm at it. the fuel valve is the on, off, reserve type (part #4)

[TOOLS1]

It seems like someone must have replaced it then. The crud is probably the problem.
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[shinyribs]

That stand alone vacuum valve is unusual. Where are you located? Maybe it's a different setup than the bikes in the States got?

[Jimboslice]

 she runs great now! should have taken a photo of the s*** that came out of it. im over in Michigan. this is the second set of carbs on the bike with the vacuum valve (purchased on eBay from California)