Vacuum fuel cock conversion question

[kurtj]

Looking to convert a 1980 gs750et vacuum fuel cock to a manual one. Bike Bandit offers both in their schematic under fuel. Has anyone done this? Does it fit? Is the fuel flow about the same? I know the fuel line is an issue, because my vacuum fuel cock feeds the carbs to the left rear. The manual one feeds the carbs to the right. Close to where my frame tube is. If anyone can comment on this, I would appreciate it. My bike is running better, but #2 plug is fouling wet. Fuel back feeding from the fuel cock. I would like to eliminate that with the manual fuelcock.

[Steve]

As abominable as the '80 petcocks were, I think you might like to put in a new OEM petcock. Besides worrying about which way the hose goes, you also need to make sure they are not too long (distance from tank to end of petcock) and that the bolts have the right spacing. After you get it installed, you will have to remember to turn it ON and OFF every time you ride. For that amount of attention, the price of OEM starts looking attractive to me.

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[doctorgonzo]

As abominable as the '80 petcocks were, I think you might like to put in a new OEM petcock. Besides worrying about which way the hose goes, you also need to make sure they are not too long (distance from tank to end of petcock) and that the bolts have the right spacing. After you get it installed, you will have to remember to turn it ON and OFF every time you ride. For that amount of attention, the price of OEM starts looking attractive to me.

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Yep, you only have to get off and forget to turn it off once before that Vacuum petcock starts to look like a mighty good idea.

[Dogma]

As abominable as the '80 petcocks were, I think you might like to put in a new OEM petcock. Besides worrying about which way the hose goes, you also need to make sure they are not too long (distance from tank to end of petcock) and that the bolts have the right spacing. After you get it installed, you will have to remember to turn it ON and OFF every time you ride. For that amount of attention, the price of OEM starts looking attractive to me.

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+1

I finally did what the experts here said and replaced mine a couple years ago. No problems since, and I only think about it in springtime when I need to prime the carbs.

[jmlcolorado]

Im building a bobber style bike and have a honda tank on it now. It will have a manual petcock once its finished.

What are the repercautions of leaving it open when not running?

[robertbarr]

You lose either way with a manual petcock. If you forget and leave it on after riding the bike, you risk a garage floor covered with fuel. If you forget to turn it on when you start your ride, your bike will run -- maybe just long enough to get you into harm's way where you'll need acceleration at the moment you exhaust the fuel in the bowls.

There are definite safety concerns, and I find it ill-advised to ditch the OEM petcock.

[jmlcolorado]

okay my old honda shadow had a manual one. never had to play with it.

And my yamy seca too.... if i remember correctly. been a while

[rudy]

I have two manual petcocks on my 650, one on each side of the tank. The last two years, that was the only bike I rode. Same on my 400, but a single petcock. Never forgot to turn them off as it was my regular shut down procedure and became a habit.

I'd say that if you ride more than one bike regularly during a season with different petcocks, go for the vacuum replacement. If you only ride one bike or all your bikes are manual, go for the manual. It'll become habit for you to reach down and turn it off when shutting down.

Just my 2 cents worth.

[Billy Ricks]

As long as the float valves seat properly there is little danger even if you forget to turn a manual petcock off. I run a Pingel on my 700 and at times forget to turn the petcock to off. I haven't had fuel on the floor yet.

[Billy Ricks]

I have two manual petcocks on my 650, one on each side of the tank. The last two years, that was the only bike I rode. Same on my 400, but a single petcock. Never forgot to turn them off as it was my regular shut down procedure and became a habit.

I'd say that if you ride more than one bike regularly during a season with different petcocks, go for the vacuum replacement. If you only ride one bike or all your bikes are manual, go for the manual. It'll become habit for you to reach down and turn it off when shutting down.

Just my 2 cents worth.

Off topic yet similar, I run GSX-R rearsets on my 700 and that necessitated flipping the shifter linkage over the wrong way, now it has a GP shift pattern. I went ahead and flipped the linkage over on the GSX-R so they both shift the same. I've gotten so used to the GP shift pattern it's hard to get on another bike with the standard shift pattern.

[chef1366]

As long as the float valves seat properly there is little danger even if you forget to turn a manual petcock off. I run a Pingel on my 700 and at times forget to turn the petcock to off. I haven't had fuel on the floor yet.

I run a pingle and it doesn't leak for the above reasons.
I never turn it off.

[Steve]

What are the repercautions of leaving it open when not running?

As long as the float valves seat properly there is little danger even if you forget to turn a manual petcock off. ...

If all things are working as they should, you could leave the petcock on forever. However, the other common-failure item in the fuel system is the float valve in each carb. If they are sealing well, there is no problem, as Billy Ricks has indicated. However, if even one of the four leaks just a little bit, you can overflow that float bowl. The earlier VM carbs (not like yours) have overflow vents with a tube that directs the gas away from the engine. The BS carbs (like yours) don't have that vent, so gas will just find any way out that it can. It might find a way to drip onto the transmission cases or it might stay in the engine and run down the intake runner into the head. If the valve is open, gas will fill the cylinder. It might drip past the rings and fall into the crankcase, diluting the oil. Depending on just how much might still be on top of the piston when you hit the starter button, it can cause a hydraulic lock situation and bend a rod when you try to start it.

In other words, there's not much to worry about.

In still other words, if you do decide to go with a manual petcock, you have to decide every time you get off, just how lucky you feel and how much you are wanting to trust parts that you can't see to judge their condition.


By the way, the correct spelling is "repercussions", but I kinda like the "CAUTIONS" part in your version.
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[jmlcolorado]

If all things are working as they should, you could leave the petcock on forever. However, the other common-failure item in the fuel system is the float valve in each carb. If they are sealing well, there is no problem, as Billy Ricks has indicated. However, if even one of the four leaks just a little bit, you can overflow that float bowl. The earlier VM carbs (not like yours) have overflow vents with a tube that directs the gas away from the engine. The BS carbs (like yours) don't have that vent, so gas will just find any way out that it can. It might find a way to drip onto the transmission cases or it might stay in the engine and run down the intake runner into the head. If the valve is open, gas will fill the cylinder. It might drip past the rings and fall into the crankcase, diluting the oil. Depending on just how much might still be on top of the piston when you hit the starter button, it can cause a hydraulic lock situation and bend a rod when you try to start it.



In other words, there's not much to worry about.

In still other words, if you do decide to go with a manual petcock, you have to decide every time you get off, just how lucky you feel and how much you are wanting to trust parts that you can't see to judge their condition.


By the way, the correct spelling is "repercussions", but I kinda like the "CAUTIONS" part in your version.
.

Thanks steve! After reading that, i might just try to find a fuel cock that has a vacume valve on it then. Might be tough considering im not even positive what this tank came off of. I know it was an 83 honda (looks similar to a nighthawk) but i couldnt fine any other markings in the bike.

I wrote the vin down to see if i could identify it that way but i misplaced it I know that it nothing special as the tank has a simple treaded nipple to mount it on.

BTW, thanks for the correction on the spelling. I had been up for hours reading posts all over the site. Seems i might have a slight addiction spending time on forums. Im a member to a Cummins forum too and have been known to spend more hours on that one a week then i work. And i still put 50- 60 hours in a week. Makes it hard to wake up in the morning

This forum is turning out the same way. Heck, yesterday i got on right as i walked in the door from work....... oh and the same today

[kurtj]

Steve, I appreciate your input back to me on this. I have been playing cat and mouse with fuel and or ignition issues for a while now. I admit I get very frustrated at times with the troubleshooting. But, I am a tinkerer and do like a challenge. This bike has force me to really use skills I haven't in years. I will stay with the OEM petcock. I was thinking of a rebuild kit, but I don't think it will be worth the risk of possible continued issues after rebuilding the petcock. I have to remind myself that I am working on a 28 year old motorcycle with mostly all original parts on it. Got to cut her some slack once in a while and put on some new parts. Part of the job.

Thanks again!

[Baatfam]

Say what you will, but the Pingal is a nice piece...just turning it on is a sexual experiance...

I never had a vacuum petcock before I got my Suzukis....
One of the first thing I did was replace it...
My dirt bikes, my Harleys, my drag bike, everything had a simple on/off petcock...
I like simple...less to go wrong...