Need help, carb overflow problem

[Anonymous]

Okay, so I finally get my float valves in after waiting almost two months. Got them in, turned the gas on and the first two carbs STILL dump gas out on the crankcase! Exactly the same as before. What can cause this besides bad float valves? It seemed to start after I had the carbs apart to change the jets a while ago. The number two carb started dumping gas. Figured I got some dirt in something, so I took them apart again and super-cleaned everything. Then number one AND two were dumping gas! I'm fully bumfuzzled.

Anyone got any ideas? Or want a slightly shotgunned 85 Katana?

 

[Anonymous]

Did you set the float level, maybe the float is never reaching the shutoff point and it is overflowing. I would check the float level and make sure they are not hung up and in fact are working, maybe they are adjusted too high and they never reach the point where it closes the valve.
Or maybe they have small holes in them or a crack to let in fuel and they fill with fuel and stay sunk rather then raise and shut off Don't have any other suggestions except that...
Good Luck...

 

[Anonymous]

Thanks for the reply. I did check and the floats are all at the same level, so it seems like even if it's wrong, they'd all overflow. I also checked to make sure the floats actually float.

The weird thing is that the float bowls on the carbs that are overflowing don't seem to fill up. They seem to fill about half way and then dump out the overflow. Also, it doesn't do it with the engine off. As soon as it fires, it dumps gas all over.

 

[frosty5011]

Marcello,

Try and test the carb rack on a bench first. I have 4 little clear plastic drawers (from one of those cabinets for holding assorted hardware), that are just a little wider than the floats on the carbs. I can put the assembled rack right on top of those and then start putting fuel into the carbs via a longer hose and the fuel tank which I also have on the bench, set slightly higher than the carbs. I'm sure, with some looking around, you can also find 4 suitable containters.

This also allows me, not only to check for leaks, and to see which carb is leaking when I suspect a leak, but also see visually if all the fuel levels are really identical to each other.

Just don't smoke a cigarette when doing this! 8O 8O 8O 8O

Sometimes, it might be difficult to see where the leak is, if there is one, this way. If that is the case, then I set the carb rack on the bench WITHOUT the 4 fuel catching containers (just set it down on the main jets); keeping it held upright by my little bench vise which just needs to grab any one side of the carbs, and put 4 wooden shims (just large enough to close the float valves) under the floats. Then just start filling a clear, attached fuel hose (about 12" in length) with fuel till the hose can hold no more.

Now you can see exactly whether your float valves seal 100%, or if not, where the leak is.

 

[Anonymous]

Right, starting the motor creates negative pressure in the combustion chamber. This negative pressure works on the diaphram of the fuel cock.
That is why when you start it up it draws fuel, The needle valve is what allows fuel into the carb, if there is anything between that valve and the seat it wont close, or the seat could be wore out or the needle valve could be wore out. That is what allows the fuel into the bowl nothing else.
When you check the hight of the floats make sure the float arm is in contact with the needle valve otherwise the adjustment will be off, even if all the adjustments are the same if the arm is not making contact against the needle valve it will be off. the floats also need to move freely up and down, if they are hanging up correct adjustment or not they wont shutoff the valve. Also why isn't the motor taking on the fuel? does it run, sputter, what is happening when it starts, maybe there is a problem with the routing of the fuel thru the carb, a blocked passage, maybe it isn't the floats at all but something along the line of tranfer to the engine something blocking the flow of fuel and it is coming out the back instead.
How can you tell the bowls are only 1/2 full with fuel and what overflow are you referring to. A vent port? I am trying to picture where the fuel is actually coming out.
If the engine is running it should take the fuel right? only if the engine was stopped and it kept taking fuel it would overflow, but when it is running since it is a demand system it can't take more fuel then what it can handle, sounds like you should check the passages in the carbs for blockage because with it running it shouldn't overflow, I mean the engine would take the additional fuel and the rpm would in fact increase like if you opened the throttle calling for more fuel. Something is blocked...
Good Luck/// just trying to help

 

[ptm]

I had trouble with mine doing that after a rebuild. Drove me crazy - one would leak, so I would thake them off ond clean them again (even changed the valve on one) then when they were back on another one (or two) would leak. I finally figured out that the float must be getting cocked a bit in the bowl from having them tilted while wrestling with them to get them back in, so it wasn't moving and pushing the valve closed. I put all the vent hoses over to the side so I could see which one was doing it then, without starting it, put the petcock on Prime. Whichever carb was spilling I would tap on the bowl with a piece of wood or a plastic screwdriver handle. That seemed to jar the float enough to get it to start floating and I haven't had a problem since.

 

[Anonymous]

Whooo! Fixed it

I can't express how much I appreciate you guys' input. And.. this is where things get stupid. Since I deleted my airbox, the two vent tubes to the float chambers were open. Guess somehow I'd assumed that these were vacuum ports and that one went to the petcock. So I plugged the other one. Dumb. Apparently doing so creates a vacuum in the float chamber, prevents it from filling completely and causes fuel to dump out.

Kinda sucks that I blew two months of riding on something that stupid. :roll:

 

[Anonymous]

Hey whatever works, I have learned more from my mistakes then my triumph's. I had a feeling something was not right, although I have read other people have removed the vent hoses all together and their bikes ran better, but you can't plug them. Sounds like not a bad idea since you want air getting to the carbs and it is restricted in 1/4 inch hoses somewhat. Seems removing the vet hoses actually have improved the performance. Right now my carbs are sitting in my kitchen waiting for new kits but I might consider removing the vent hoses and see how it runs. that is what is great about this website, people you don't know willing to offer help. Sometimes all you need is someone to ask the right question to get you on track...
Anyway at least you solved your problem, you came you saw and you kicked it's A**, Way to Go....