Help needed... Needle at bottom of carb is leaking gas

[Klay23]

I searched but no no avail.

1979 gs 750, no airbox, bought a junker and no telling what as is missing. Finally cleaned the tank and lined it, found some pods for the missing air box and put them on. Got the battery charged and all seemed to be good to go. Installed the tank and flipped the petcock to on, and watched the gas fill the inline filter I added(cautious). Started checking for any leaks and immediately saw the gas leaking out of the very first carb closest to me. I'm standing on the right side of the bike... Where do these little valves need to be going? Is something missing?

[Klay23]

Found the 750 service manual... Its page 17 and its the carb under cylinder 4, mostly. 3 is also leaking slightly

[chuck hahn]

The very bottom nipple on the bowl is an overflow. Nothing should be coming out of it. The 2 things that will cause an overflow is a stuck open float needle or the float height is set wrong. First tap on the bowl with a wrench and see if it stops. Second, be absolutely sure the float hts are correct.

A piece of vacuum line goes on them and they collect between the tranny and the swing arm and are left open so IF an overflow happens while your riding the gas is channel away from the hot engine and your legs. I run them long and then snip them off from under the bike once I have them all fished thru. Leave 2 inches or so hanging down

[chuck hahn]

Oh..and wipe the bowls off and have a flashlight handy to see up in there real good. Gas leaking from the bowl gasket or from the fuel tubes can run down and drip off the overflows..so wipe and immediately look ( with the gas on PRI ) and see that none of the gaskets or orings in the fuel tubes are leaking

[Klay23]

Oh..and wipe the bowls off and have a flashlight handy to see up in there real good. Gas leaking from the bowl gasket or from the fuel tubes can run down and drip off the overflows..so wipe and immediately look ( with the gas on PRI ) and see that none of the gaskets or orings in the fuel tubes are leaking

Fuel tube isn't leaking, only the overflows...

[chuck hahn]

Stuck float or a wrong float ht I would suspect. Drains aren't leaking and are tight???

[Klay23]

What do you mean drains? Newbie, but read pretty well, lol

Need a picture book, hahaha

[chuck hahn]

Plug on the lower side of the bowls..or a screw into a recessed hole. Theres an oring on them that can weep and drip off the overflows..that why I said wipe the bowls dry and take a look around with a flashlight. Leave on PRIme so you've got gas flow and try to find whats getting wet after you wipe each one off. It wont take long for a wet spot to start again.

[Klay23]

So I tried the tapping with wrench... NOW no flow of gas at all, like a reverse vacuum or something? Maybe I clogged the cheap fuel filter...hmmmm?

[Klay23]

Stuck float or a wrong float ht I would suspect. Drains aren't leaking and are tight???

How much is the float actually supposed to move? Doesn't look like its moving at all, maybe stuck open? That make sense?

[chuck hahn]

The float will move up and down maybe 1/2 to 3/4 inch..making the needle go up and down about 3/8 inch or so. I was thinking to ask if you have the vents on 2 and 4 capped off. If yes, uncap them. The carbs need the atnospheric pressure to equalize the fuel levels uniformly.

Nipples on 2 and 4v are vents and the one on 3 goes to the petcock. This is for the VM carbs.

CV carbs have the suction to the petcock on the back side of carb 2s throat. Right behind the top cover.

[Klay23]

The float will move up and down maybe 1/2 to 3/4 inch..making the needle go up and down about 3/8 inch or so. I was thinking to ask if you have the vents on 2 and 4 capped off. If yes, uncap them. The carbs need the atnospheric pressure to equalize the fuel levels uniformly.

Nipples on 2 and 4v are vents and the one on 3 goes to the petcock. This is for the VM carbs.

CV carbs have the suction to the petcock on the back side of carb 2s throat. Right behind the top cover.

No caps on the overflow needles on any of them...

Nowhere for me to attach anything back to the petcock, aftermarket tank unfortunately... .???

[Klay23]

The float will move up and down maybe 1/2 to 3/4 inch..making the needle go up and down about 3/8 inch or so. I was thinking to ask if you have the vents on 2 and 4 capped off. If yes, uncap them. The carbs need the atnospheric pressure to equalize the fuel levels uniformly.

Nipples on 2 and 4v are vents and the one on 3 goes to the petcock. This is for the VM carbs.

CV carbs have the suction to the petcock on the back side of carb 2s throat. Right behind the top cover.

Easiest way to tell if I have cv or VM carbs? What do the initials actually mean?

And seriously, thank you, I'm trying my best to learn...

[chuck hahn]

VMs have longer rectangualar shaped tops with two little what I call "wings".

CVs have a square top that looks like a flat hat and 4 bolts in the 4 corners.

Throw up a picture of what you have.

[Steve]

Just clicked on this thread for the first time and I see several things happening.

1. In the original post, you "flipped the petcock to on". These petcock don't have a position called "ON". They do, however, have one called "RUN", which is with the lever pointing straight down. THAT is where the petcock should be about 99.9% of the time. If you are running low on fuel, rotate the lever clockwise, so it is pointing forward to the REServe position, you will be able to use the last gallon or so in the tank while you find a gas station. In both of those positions, a properly-operating petcock will flow fuel when the engine is running and stop flow when the engine is stopped. If you rotate the lever fully anti-clockwise to the PRIme position, fuel will free-flow. This is only used if you have not ridden your bike for several weeks or have drained the float bowls for some other reason. If you use the PRIme position without the engine running, it is possible to overpower weak float valves and cause some overflow.

2. Terminology. What is the "needle at the bottom of the carb"? The only two needles that I know of are the float needle, which is inside the carb and allows gas to fill the float bowls and the needle that goes up the middle (also inside the carb) to control fuel flow through the needle jet for mid-range fuel metering. There are no needles visible from the outside.

3. You "need a picture book"? Click HERE for your picture book.

4. You "tapped the carbs, now no gas flow". If it was a stuck float valve, tapping on the carbs will sometimes dislodge the problem, allowing the float valve to work properly. When the bowls are filled to the proper height, no more gas will flow until the engine uses some or you wait long enough for some to evaporate.

4. There is a "cheap fuel filter" installed. Why? You said you had just lined the tank, it should be CLEAN now. There is a filter on the petcock that should take care of everything downstream. Too many times, an automotive fuel filter is installed. The problem with those is that they are designed to be used with cars that have fuel pumps. A fuel pump will push fuel through the rather restrictive filter media. We have gravity-fed systems that do not generate enough pressure to do that. If you insist on using an external filter, go to Lowe's, Home Depot, Auto Zone, wherever, get a filter for a lawn tractor. Most of them also have gravity-fed fuel systems.

5. Your '79 bike should have the VM carbs. As mentioned, the VM carbs have a cap that is sort of a domed rectangle that is held on with three small screws. The '80-and-newer four-cylinder GSes came with what are known as "CV" carbs. They have a much larger cap that is square-ish with a raised round dome inside the four cap screws.

What to the initials stand for? VM is the model name of the carb. Your carbs should be VM26SS for the full name. "CV" is actually a type of carb, and it stands for "Constant Velocity", referring to the way a vacuum-operated slide controls the velocity of the air over the jets. If you wanted to refer to them the same way as the VM carbs, you should call them "BS" carbs, for their model name. The '80 750s came with BS32SS carbs.

There were many other manufacturers that also made CV-style carbs, each, of course, had their own model name for them, so it just seems a bit strange to me that we refer to one model by its name and the other model by the way it works.

6. You installed pods. Hopefully, they are better than the cheap EMGO pods, but somehow, I doubt that. Either way, I hope you have re-jetted the carbs for the pods.

7. You are "standing on the right side of the bike... Where do these little valves need to be going? " What "little valves"?

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