Fuel nightmare

[Anonymous]

I have a GS 850 G , with 4 carbies *@%^$*@%^$*@%^$*@%^$in out fuel from the rear into the air cleaner box. I have had them all out cleaned. I am new when it comes to carby problems, can anybody please help before I spend heaps of dollars at a workshop.[/b]

[Dink]

The needle and seat is leaking allowing fuel to continue to run , this is because of damaged o-rings,these sit under the seat, damaged needles, the "points" should be a smooth taper, no groove detectable, or just that the float level is to high. Or one other possiblity is that the fuel tap itself is damaged and is not stopping flow which is pushing fuel past the needle and seat.
Dink

[argonsagas]

Dink has covered pretty well all the possibilities.

You can find a full description of carburetors on this forum, in the Technical section titled "carb cleanup"

The first thing you should check is easy. That would be the fuel flow.

Do you have a single tube between the carbs and the fuel tank, or two? I am not certain of the petcock used on earlier 850's, but the later ones have two lines. One is for fuel to flow to the carbs, and the second is a vacuum to open a valve inside the petcock while the engine is running. When not running, the lack of vacuum closes the valve and fuel will not flow.


Check the position of the lever on the petcock. It should be in either On or Reserve, but NOT in Prime. In PRIme, the valve mentioned above is bypassed, and fuel can flow all the time.

If fuel is flowing in all lever positions, you need a new petcock, or a kit to rebuild it.

You can re-set the float levels and see if that makes an immediate difference in fuel flow. When closed you should have a positive seal, with NO leakage at all.

If not, you definitely need to replace the O-rings in your carbs, and perhaps the needles as well. (These are the small needles that sit in the fuel bowl at the bottom of your carb, and move up and down just a bit, their movement controlled by the float.)

As Dink said, check the tapered ends for ANY imperfection. They must be absolutely clean and have no nicks or marks.



On the subject of clean.....you should also install an in-line fuel filter between the tank and the carbs. It will prevent sediment or rust particles from reaching your carbs, and is the cheapest insurance you can buy for your bike.

[Anonymous]

It's the needles not seating or soggy floats. Even if the petcock is on Prime, it shouldn't pour fuel out of the carbs like that. Check float levels, inspect (better yet, replace the needles), and see if the needles are sticky. Sometimes, with an empty bowl, the floats will drop so low that they don't have enough leverage to close the needles and the fuel will just run (happened after I cleaned my carbs out). Try tapping the side of the float bowls with a screwdriver handle with the petcock on Prime and see if you can get it to stop. If not, go through the carbs.

[Anonymous]

I had the same problem on my GS 650 GL. I got advice on carb problems for months with no avail. It turned out to be the intake valves not seating in the head. On the compression stroke, the fuel was just blown back out, not to mention, when air was forced backward through the carbs, the diaphram went up again letting even more fuel spray backward. Before you go tearing into those carbs, do a compression test to be sure its not an intake valve problem.

[nert]

is it "*@%^$*@%^$*@%^$*@%^$in" when running, or with engine off on the center stand?

[Anonymous]

Hi, small world the exact thing happened to me on my GS850 this weekend when I accidently swithed it to prime instead of reserve while out riding. Once parked, gas was dripping from the left side of the intake and the airbox. Swithing the petcock back to on cured the problem.

If thats the issue, make sure you check for gas leaks before you ride, and have a fire extingusher handy. I heard that gas stuff is flammable!!! If that doesn't fix it, you'll have to go through the steps in the above posts to fix. Good luck!!!

[nert]

thebear

i don't think your problem is curred. even in prime position, the fuel should not leak past the float valve.

[Anonymous]

Nert, I wondered about that but I think I'm ok since it isn't leaking when i switch it to prime while it isn't running, and it hasn't leaked since. I'm assuming while running it in prime its just somehow sucked in too much gas.

Or am I missing something?? If its leaking, wouldn't it be running rich? It isn't running rich, thats for sure.

[nert]

Prime psition allows fuel to flow with out the engine running. Just like a manual on/off petcock. In run and reserve, engine vacuum is used (meaning the engine is running if vacuum is present) to open the valve and aloow fuel to flow. So, if engine is off, fuel flow to carburetors is off. In prime fuel is allowed to flow to the carbs, but as the fuel bowl floats up, the valve is pressed into the fuel bowl jet to stop flow. Possibly you have a fuel float incorrectly set, possibly there was a piece of dirt in the valve not allowing the valve to seat and stop fuel flow. Possibly (on a limb here) fuel tank vent is plugged, heat from the engine caused pressure in the tank, since the valve was in prime position, fuel was forcing the valve off its seat and spilling into the air box due to the higher fuel pressure in the tank.

[Anonymous]

nert, thx for reply, sounds like something is wrong then...I'll check the vent, and carbs will be rebuit this winter so I'll check float level then. It shouldn't leak whether its running in on/reserve or prime, so now I'm curious. I am going to try to recreate the problem (engine running, switch to prime with engine running). thx again.

[Anonymous]

More likely it is a leaky needle. As long as the engine is running, it is just burning the excess fuel, but when stopped, it's spilling out the vent.

[Anonymous]

Fuel Nightmare

Thanks to everybody that replied to my question on carbs.Just to let anyone whos interested know I replaced the needles and seats and orings and the problem is solved and I have never felt the bike run so good.

[Anonymous]

I have a similar problem

My 1980 850 will run really well if sprayed with something alot more flammable than gas such as starting fluid. But it will not suck gas out of the carbs at all unless I artificially cause a massive vaccuum with my hand. Then gas is pulled up from the bowl into the venturi and that cylinder only will fire and try to run for alittle while untill the venturi run dry again. Do you think I have bad valves? How do I fix this? Is it a difficult fix? Does the 1980 gs850 have overhead cams with a cam chain? I can do the work provided I don't have a cam chain to deal with.