Stuck fuel floats? Runs on 4, then 2 cylinders

[Anonymous]

I just overhauled my carbs because of a stalling problem, installed new jets, o-rings from carb kits, now it will run really good for a minute or so, then the outer 2 cylinders will quit working (#1 and 4), and it will sometimes continue to keep running on the #2 and 3 cylinders, or it will just die out. The outer 2 cylinders' pipes will be cool to touch, the inner 2 pipes, hot. If I tap on the float bowls of the 2 non-working cylinders (#1 and 4) with a rock it will free something up and it will run on all 4 for a minute or so very well, then those outer 2 will start to shut off again. Its definitely a carb issue, are the floats stuck or is something else and how do I adjust them. thanks in advance

 

[KEITH KRAUSE]

If tapping the bowls to 1 and 4 helps temporarily, then it's definitely a problem with fuel filling the bowls.
I would think that rust or dirt is clogging the passage at the float needle valve seat. Is the tank clean? How well did you clean the carbs? Could also be a burr on the float valves causing sticking.
Could also be floats that are way out of adjustment and allowing a very low fuel level that's helped by the tapping. I even remember a member recently that had some floats in upside down. This should result in almost no fuel at all in the bowls, but it's happened, so I thought I'd mention it. In the case of upside down floats, tapping the bowls would possibly help for a moment.

 

[Anonymous]

I cleaned the carbs really well when I did the carb overhaul, used about 10 cans of carb cleaner. Installed new float needles with seats also. I did clean the tank out with a garden house, shook out a lot of sludge, but I did still see some particles thru the glass fuel filter (cleaned the fuel filter also) once I put the tank on, put gas in it and hooked it up to the carbs. So maybe there is something clogging up the float needles. Also, the bike sat for 3 1/2 months with gas in it after I did the carbs so maybe that has something to do with it (had to get it registered before I could ride it)

 

[KEITH KRAUSE]

Well, the hole in the float valve seat is small, so rust particles can accumulate and block it easily. And 3 1/2 months can allow the gas to build up a sticky varnish film. Doesn't take much to make a float valve stick.
If you have rust, you need to seal the tank first or you'll just have a constant problem. As for the carbs, if you have a stubby screwdriver, you can remove just the bowls and remove the valves and seats for inspection/cleaning. Be sure to lay a towel down so you don't lose anything if you do this. Then put a pan down to catch fuel and put the petcock on prime to allow the carb passages to the bowls to flush out. Putting the float valves back in while inserting the float and the float pin takes a little finger dexterity but it may save you some work. You can also check for smooth float travel and be sure the float valves aren't hanging up before buttoning things up.
PS: I suggest replacing the stock Phillips bowl screws with Allens.

 

[SqDancerLynn1]

You said you washed the tank with the hose ??? you could havewater in the gas / & in the carbs

 

[Anonymous]

The way I look at it is its better to have a little water in the tank than big chunks of sludge. Anyhow, I pulled off the float bowls as Keith suggested and the carbs still looked clean inside. I took off the float needles and seats also and those were free and clean as well. The floats were not in upside down and the float height seems to be adjusted right. With the needles and seats off, I turned the petcock to prime and noticed that more gas seems to pour out the #2 and 3 carbs than the #1 and 4 carbs. Then I pulled the fuel line off from the carbs and let it pour out into a gas can and noticed that the amount coming out was not nearly as much as it should be, so maybe that is the reason for those 2 cylinders not to work sometimes, I just wonder why the other 2 were able to, and why tapping on the float bowls would make a difference. Anyhow, I think if I remove all the rust from the tank and get a good constant stream to pour out from the gas tank that it will solve the problem. I have muriatic acid here at home that is used for the pool, I could use that for rust removal, or I could go the vinegar route, but that I will have to buy from the store. Any ideas on which way I should go for cleaning out the tank? Also, I called a local radiator shop and they said they would acid wash the tank and coat the inside for $125 which is way too much to spend. The bike is a 77 GS750 and is not worth putting that much into it.

 

[KEITH KRAUSE]

Kreem costs about $30-35. It has a rust stripper that you follow by coating the tank. Some say it's hard to use, others not much of a problem. You have to keep turning the tank until you feel it's all coated. Then drain any left over and keep an eye on it 'til it starts drying. I've seen people walk away from the tank too soon just to find "stalactites" forming inside. You have to make a temp seal for the gas cap and petcock holes. I think the directions are easy to follow.
I don't know what else to say about your other problem. If tapping the bowls temporarily helps, then it must be fuel flow related. Something's blocking the fuel flow in the passages or the float and/or float valve is not operating right. To measure the float height accurately, the carbs must be inverted. If you had rust particles building up and blocking the flow at the valve, you should see a lot of rust settling to the bottom of the float bowls too. The rust would fall with the fuel after you tapped the carb. I don't know if the fuel coming out into the #2 and 3 carbs at a greater rate is a sign or not. It could just be that the two closest carbs will "hog" the majority of the fuel flow, especially with the bowls off. I do think that with the bowls on, the inner carbs fill up just a bit sooner than the outer carbs. They are closer to the source. This isn't something significant anyway. You could have a weak flow coming from the petcock, but if it can fill the inner carbs, it wouldn't take much longer to fill the outer carbs.

 

[KEITH KRAUSE]

I'll add that these carbs will have mixture problems if they're not vacuum synched. It's very important.
If tapping the carb helps, and it's not a fuel blockage, I have to wonder if #1 and 4 slides are hanging up a little and tapping the carbs makes them drop. If a slide(s) is just a bit higher than the others, that carb will have comparatively less vacuum to draw fuel from the bowls. Tapping it could make it settle and then it would draw fuel at a more equal rate. I've seen sticking slides before, but not ones that have caused your problem. Only "high idle" problems.