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Need help with gs 850 fuel system

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Hey, newbie here. Had a 1980 GS850L given to me. It had been sitting for 4 years. I cleaned the carburetors, changed tank(old one was rusty), new tires, etc. It won?t pump gas to the carbs. I first thought that the fuel cutoff valve lever was broken off but after looking on eBay to get a new petcock I see that there is no cutoff valve. Could somebody explain how the petcock functions and maybe diagnose it?


thanks
 
4_B80202_C_7893_4_A31_8056_8_B5_B68_D38722.jpg
 
Hello and welcome. The fuel petcock is vacuum operated. By that I mean there is a vacuum hose, usually the one from #1 or #2 carb, near the cylinder head, which connects to the fuel petcock. When cranking or running intake vacuum is created and opens a valve in the petcock allowing gravity to feed fuel into the fuel line and into the carbs.

As for not seeing the "cut off valve" that is normal for the L series bikes. If you look closely you'll see a screwdriver slot where that lever would normally be. Don't put a screwdriver in there and start twisting it around. You'll be tempted to do it but DON'T until you know exactly what you're doing.

If the bike sat for 4 years and you are not experienced at cleaning carbs, I doubt that you got them really clean enough to actually run and idle. There are many How to's and Youtube videos explaining in detail how to clean the carbs. It's not just a matter of taking the carbs out and the bowls off and cleaning the grunge in the float bowls. Much more involved and precise process to clean carbs. Don't feel bad. We all started somewhere and in the beginning it would take 2 or 3 or even 5 times pulling the carbs to really get them clean.
 
I’ve cleaned carburetors before but even if I didn’t get them completely cleaned I know there is no fuel getting through the gas lines. I put an inline filter in and I can see that gas isn’t being pumped(filter is transparent). I assume the valve is shut off. How do you turn it? Thanks for the info.


Edit die to add:
on second thought you said it gravity feeds to the carbs. Maybe the extra couple of inches of hose I added on the other side of the filter lifted up to high so that it doesn’t flow?
 
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Turn the fuel tap to PRIME and gas should flow. If not, then the fuel tap is blocked regardless of whether the vacuum part is functioning.
 
Yes, fuel flows by gravity...petcock must function correctly and tank cap must vent.
the 1980 petcock is an oddball- the screwdriver slot sorta gives you a prime spot but it might be clogged. Don't fiddle with it, just get new one like this guy sells for $50

http://www.georgefixs.com/1980-gs550-gs750-gs850-gs1000-gs1100-petcock/

this assumes your replacement tank is also from 1980 model. If not, there are better petcock choices. If you just want to see bike sorta run,rig up an auxilliary fuel supply tank to bypass petcock
 
The leverless petcock doesn't have a prime like most other petcocks. The details of how the petcock works is explained in detail in the factory service manual. It needs vacuum to activate the prime and a check valve in the petcock back cover keeps the diaphragm open thereafter without vacuum. This check valve often fails though so be warned about that. A new factory OEM petcock is recommended. I bought one of those cheap Georgefix petcocks for one of my bikes, which look same as the OEM petcock, only the check valve was bad out of the box. Maybe just bad luck or maybe they are just cheap clone part junk. Not sure which.
 
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jdvorchak said:
The fuel petcock is vacuum operated. By that I mean there is a vacuum hose, usually the one from #1 or #2 carb, near the cylinder head, which connects to the fuel petcock.
Click to expand...
On your bike, it will be on carb #2. The carbs are numbered from left to right, as you sit on the bike. #1 would be under your clutch hand, #4 would be under your right hand.

jdvorchak said:
As for not seeing the "cut off valve" that is normal for the L series bikes. If you look closely you'll see a screwdriver slot where that lever would normally be. Don't put a screwdriver in there and start twisting it around. You'll be tempted to do it but DON'T until you know exactly what you're doing.
Click to expand...
That is actually more related to the 1980 bikes than the "L" bikes. Somehow, the 850G and 1000G bikes escaped the "dreaded '80 petcock", but I think all the others had that petcock without a lever. If I remember correctly, with the slot horizontal, it is in the RUN position, where it should flow fuel when there is vacuum applied to the diaphragm. When the slot is vertical, it is in the PRIME position. In that position, it does take one "puff" of vacuum to release the valve to allow fuel flow, but will then keep it flowing until you run out of fuel or the petcock selector is moved. It should generally be left in the RUN position. Note that there is no RESERVE position on this petcock, so it will be important, no, CRITICAL, that your fuel gauge works properly.

Machinegunner said:
I put an inline filter in and I can see that gas isn’t being pumped(filter is transparent). I assume the valve is shut off. How do you turn it? ...
on second thought you said it gravity feeds to the carbs. Maybe the extra couple of inches of hose I added on the other side of the filter lifted up to high so that it doesn’t flow?
Click to expand...
Depending on what fuel filter you added, THAT might be part of your problem. An automotive filter is designed for a system with a fuel pump that will force fuel through the rather restrictive filter membrane. The only "pump" on our bikes is a little bit of gravity. And, as far as your couple of extra inches, length does not matter. As long as the TOP of the fuel in the tank is higher than the fuel in the carbs, it should flow.

Four things that can hinder that:
1. Faulty petcock.
2. Vacuum hose not connected between carb #2 and petcock.
3. Restrictive fuel filter
4. Carb float valves stuck closed.

.
 
Wow lots of replies. Thanks everyone. I will try putting the hose directly in a gas can to see if it runs. If so I?ll probably get a new petcock. So will a 850g petcock fit? I presume not. I am not sure what tank I put on it. The guy who gave me the bike had it since he bought the bike. Fuel did leak around the petcock when I first put it on. I assumed this was due to a faulty gasket so I used rtv on it.
 
I dont know anything about a leverless petcock but you can simply check its operation by putting a 1/4 hose to the vacum side of the petcock and sucking. If the petcock is working gas will immediately start to flow from the fuel side of the petcock.
 
Skip the rtv and get the correct washers for the petcock mounting bolts - they are rubber bonded to metal, about 45 cents each at a decent hardware store. Your style 1980 petcock has 50mm centerline mounting bolt spacing - others have a 44mm spacing.
 
Suzuki used at least two different petcocks for the GS. The real difference is the distance between the mounting bolts. Yours will be either 34mm or 44mm center to center. Or about 1 1/4 inch or 1 3/4 inch. So when searching for a new petcock be aware of the difference.

Just my opinion but using RTV to seal a fuel leak located just below your legs is not the best choice. Those engines get hot and a fuel leak between your legs is probably not something you want to experience.
 
jdvorchak said:
Suzuki used at least two different petcocks for the GS. The real difference is the distance between the mounting bolts. Yours will be either 34mm or 44mm center to center. Or about 1 1/4 inch or 1 3/4 inch. So when searching for a new petcock be aware of the difference.

.
Click to expand...

I've never seen a GS with a 34mm petcock. What model bike? I'm not familiar with the 250/300's so maybe those?

The leverless petcock is 50mm spacing. Suzuki needed a low profile petcock for bikes switching from VM to CV carbs in 1980. I'm not positive but I think that petcock was a one year wonder.

And there are quite a few different GS petcocks. Early 750 and 1000 used tall 44mm petcocks but the fuel outlet is in different locations. The 1980 550 had a unique petcock with a prime screw. And several model CV carb bikes went back to a 44 mm petcocks in 1981 (from the leverless petcock) but with a smaller lever and lower height. I'm sure there are others but this is off the top of my head.
 
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Ed is correct (as usual :encouragement:) on all points, and there are a couple other details.

All of the leverless petcocks I have seen on a GS were on '80 models, but not all '80 models had leverless petcocks. My 850G and my son's 1000G have standard petcocks.

Yes, the leverless petcock appeared on the '80 models, but I can't say that it's because of the change to CV-type carbs, it just happened at the same time.

My wife's '82 850GL has one of the petcocks with the smaller lever and lower height. Unfortunately, that will not work for the OP.

Many of the units with 44 mm spacing can be used, but you really have to watch for overall height, to make sure you don't hit the carbs or airbox. The fuel and vacuum hoses might need to be lengthened or re-routed, due to outlet positioning, but they might work.

.
 
Not sure which model used a 34mm petcock but I ended up with a Suzuki petcock, which was 34mm, on my KZ750 because all of the KZ petcocks I saw, on eBay, were 44mm. The tank was not the correct tank for the bike but it was what I had. I could be wrong on that. It was over a year ago. But the point is to be careful with his selection of a new petcock so he gets one that will fit first time. Especially since he doesn't know what model or year of the gas tank.
 
Boriqua said:
I dont know anything about a leverless petcock but you can simply check its operation by putting a 1/4 hose to the vacum side of the petcock and sucking. If the petcock is working gas will immediately start to flow from the fuel side of the petcock.
Click to expand...

This

You guys are going on and on about replacing the petcock without even having it checked

1. Is there a vacuum hose that runs from the petcock to the top front of carb #2? If not, that's likely the cause
2. Boriqua is correct. Disconnect both hoses from the petcock, attach a hose to the vacuum port and suck on it. If gas flows, the petcock is good. If it doesn't flow, it's either clogged or faulty.
3. If no gas flows, drain the tank and remove the petcock. See if the fuel screen is clogged up

No RTV and get the correct gasket when you reinstall the old or new petcock. The bolts holding the petcock to the tank may have special washers with a seal



Post up some pictures of your tank and petcock
 
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Big T said:
This

You guys are going on and on about replacing the petcock without even having it checked

1. Is there a vacuum hose that runs from the petcock to the top front of carb #2? If not, that's likely the cause
2. Boriqua is correct. Disconnect both hoses from the petcock, attach a hose to the vacuum port and suck on it. If gas flows, the petcock is good. If it doesn't flow, it's either clogged or faulty.
3. If no gas flows, drain the tank and remove the petcock. See if the fuel screen is clogged up

No RTV and get the correct gasket when you reinstall the old or new petcock. The bolts holding the petcock to the tank may have special washers with a seal



Post up some pictures of your tank and petcock
Click to expand...

One other thing...

When the slot in the petcock is horizontal that's the normal running position. Vertical slot is prime.

With the slot vertical pull a vacuum on the vacuum line and release. If the primer feature, and the check valve, is working fuel will flow. No fuel will flow until vacuum pulls the diaphragm open. If fuel stops flowing when the vacuum stops, and the slot is in the prime position, the check valve in the cover has failed.
 
mg,

Other conversation:

Is it running okay (now that you figured out the petcock)?
If not: Please describe "cleaned the carburators"....

.
 
I will add something that is probably obvious but since there seems to be advice on what petcock you need for the year bike you have...

If you find that the petcock is faulty .. and mine was TRASHED .. just take a ruler with MM on it and measure the mounting screws center to center. Its bone simple and will remove any guessing. These are old bikes and you never know what tank might be on what bike.
 
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