GS 250 carb overflowing air filter side

[Antt98]

Hello,
I recently purchased a 1981 Suzuki GS 250t. The bike runs fine until the one intake is overflowed and then it lacks power and just wants to stall. I took the carbs apart cleaned all jets and needles. The needle to stop fuel moves freely, I can stop the fuel when I move the float by hand. The float moves freely but when I put fuel to it the fuel spits out of the overflow.

I have even swapped the floats, the needles and seats from one carb to the other, yet the issue remains on the same side.

Any help is appreciated.

[rphillips]

You didn't say if you measured to see the float height was set properly. Also there should be an "O" ring above, or on, the seat that the needle seals against... Just thinking.

[Nessism]

The float valve needle mates with the seat, as they wear in together, and should never be separated. If one or the other is worn, you must replace them as a set.

The float valve body has an O-ring which seals against the carb body. These must be replaced when messing with the carbs.

Sometimes people put fuel into the carbs via the overflow tubes. Make sure you only have fuel entering via the fuel tee between the carbs. Also, make sure your petcock isn't sending fuel down the vacuum line, and into the carbs that way. This is a common failure when the petcock diaphragm fails.

[Antt98]

I did not measure the float heights, will do that next.

The valves both seal when I push the floats manually, and without effort.

It must be the float heights.
Do both floats need to measure the same height or do they sometimes need to be adjusted differently?

[Antt98]

Good morning, I attached a picture for your reference.
YOi can see in the picture that the circled pipe is plugged with a screw by previous owner.
I found out from the service manual that this must be the breather pipe.
Could this maybe have something to do with the fuel overflow?
And what could be the reason for capping the breather? Should I open it again, where is it supposed to terminate?
Thanks.

[Rich82GS750TZ]

I haven't been through your whole manual. But this image shows actually 2 breather hoses: one connected where your screw-capped hose is; one looks to me like maybe it connects to somewhere on carb # ! ? (the left one). Hard to tell with the grainy scan of this manual. But the vent (or breather) hoses on other GSes rout to somewhere up above the airbox and terminate in still air. But it/they need to be open, not plugged.


This is the float height adjustment, for both carbs:

[Antt98]

That sure looks like 2 breather hoses, my manual only shows 1 and I can't find a picture like the one you sent.
This should help.
Now I just have to make it through the day till I get home to keep trying.

[Nessism]

If the spring in the float needle won't hold up the weight of the float, I'd get new float valve assemblies.

And both carbs need to be vented to the atmosphere. Typically, there are long hoses attached to the vent ports, and the hoses route up and lay by the airbox somewhere.

[Rich82GS750TZ]

The pics I attached are from the 250T manual on BikeCliff's Website. It's quite possible that the '81 is slightly different.

https://gsarchive.bwringer.com/

[Antt98]

I readjusted the floats, this time by measuring, and opened that breather, put fuel to it and there was no more fuel coming from the intake side. Nice.
Put it all back together primed the carbs, and it wouldn't start, left the battery to charge for a bit and she fired up with some hesitation. But ran smooth and started easily every time after that.

So I went for my first (cold) test drive, upon returning I had an oil/fuel mixture coming from the crank breather.
So I drained the oil and I had 1.5 qt of fuel in the oil... Not good.

I am pretty sure that fuel is coming from the previous days when the carbs were flooding.

Is there anything else I should check besides compression?

The bike ran very good and pulled good, although I have nothing to compare it to but my driveway is about 1/4 mile from the next road, and I wouldn't say it took me longer than 25 seconds to get there, against wind, not maxing her out.

[Rich82GS750TZ]

Sounds like you might have it licked. Put in fresh oil and run it again. Keep checking to make sure you got no more fuel running into the combustion chamber than what you should have for combustion. You could check compression if you have a tester. Be sure to have the throttle wide open when you do this. But I'm not sure that it's going to tell you much, though sometimes numbers are nice to have.

[Nessism]

Gas in the crankcase only happens when the engine is OFF. And when the engine is off there should be no fuel flowing from your petcock (unless you mistakenly have it set to Prime). So, next question: is the petcock working properly? Sometimes when they fail fuel goes down the vacuum line and into the carbs that way. Either which way, there should be no fuel flowing when the engine is off.

[Antt98]

When I checked the overflowing carb I set the petcock to "prime", carb stopped overflowing when it was set to "on".
later on I realized I don't need to hook the whole carb up just to check if it's overflowing.

I read in other forums that fuel in crankcase could mean bad piston rings. That's where the idea for compression test is from.

I appreciate all your quick replies.

[Rich82GS750TZ]

In theory, the float valves in the carbs should stop the fuel flow when properly height-adjusted floats rise and force the needle against it's seat. We know better. In practice, these valves can't stop the fuel flow if you leave the petcock on PRIME, and you end up with a crankcase full of fuel. Brand new rings and a fresh hone won't keep fuel from getting through the rings, which have gaps in them for reasons.

If the OEM petcock is functioning properly, it won't flow fuel in the ON and RESERVE positions until vacuum is applied when you run the starter.

[rphillips]

Remember before we had auto off petcocks, pre mid 70's, turning fuel off was as much of a habit as putting kick stand down. In a perfect world the needle and seats would always work, but most often, this is no perfect world