Topic: float bowl overflow

[hymodyne]

evening,

I noticed a slow but steady leak from the #4 carb overflow tube. This is a new thing, as I rebuilt the carbs saturday. I've been running the bike every day since staurday, and this is the first time that the #4 bowl has been too full. with two inline filters (the second set in as many months) and completely rebuilt carbs, float bowls set at 22mm, what have i missed?

any observations or suggestions would be appreciated. At present, I'm simply shutting off the fuel and allowing the carbs to run dry before I put it away.

hym

[Bob Wessner]

I've wrestled with this myself. My 750 floats are to be set at 26mm and I did, and checked them 3 times. One still had a tendancy to leak/overflow intermitantly. I could only guess that either I did not hit it on the mark (26mm) or there was some other variable at work. Assuming your float valves and seats are OK, as were mine, I logically assumed since it was leaking the fuel level had to be a bit high, certianly not too low so I just tweaked the level a bit and the problem was solved.

[Glenn Stauffer]

I have often had a problem where one of the carbs on my 750 overflows.  The float was apparently getting hung up since a sharp tap on the side of the float bowl with a screwdriver handle would stop the leak.  You might also want to check if that float floats or has a pin hole and fills with gas and whether there might be a crack in the overflow tube.  Sounds to me like the float is getting hung up.

--Glenn

[dusterdude]

is your overflow pipe cracked,as 3 out of the 4 of mine are.

[bryanj]

A lot of people forget to de-varnish the float pivot pin and inside the pivot hole and although they are free they aint free enough

[hymodyne]

I've adjusted the float height, bending the tab about 1mm higher on the #4 carb. when I restart, the bowl is still overflowing.
I don't want to tweek the height of the tab too much, not being sure how much a mm of tab adjustment will translate into float level (22m).

keep tweeking?

hym

[Bob Wessner]

It would help if you could see the fuel level in the bowl when filled. There have been posts in the past about modifying a 'spare' float bowl by affixing a tube to either the drain plug or breaking off the inside of the overflow and attaching a tube to what remains of the outside. Having neither a spare bowl or not liking  the tedium of moving one from carb to carb, someone suggested plastic tubing inserted in the drain plug. I went to the hardware store and found two different diameters, the first was too thick, the second, naturally, was too thin. I took the thinner of the two and spiral wrapped some teflon tape like that used for plumming threads and essentially screwed a lenght of it into all four bowls at the same time. Tape the ends of the tubes higher up on the carb sides to keep the fuel from overflowing. As long as the tubing is clear, it really doesn't matter whether it's fuel resistant, you're not going to leave it on forever. This way, you get to see all four at once, relative to one another when you turn the petcock on. Mine held-up long enough to even take pics of the levels for an earlier post here when I was having problems.. again .. with my carbs.

[stanghater]

i wrestled with this too for a week. i ended up putting in my old float needles back in. problem solved so far

[CB750F2]

You may have a sticking/binding float or a leaking float valve. The float valve can be checked in situ by removing the float bowl, turning on the fuel and then checking to see if the fuel shuts off when the float is lifted to close the float valve. Hope this helps. Pat from Nth Qld.

[n9viw]

One thing most people don't consider is this- the overflow tube in the problem carb may have a crack in it. This would drain gas out constantly, as there would be nothing stopping it. Take the bowl off and fill it to just under the top of the overflow with gas, and see if it leaks out. If it does, either your drain screw needs replacing, or the overflow tube is cracked.
A guy with a steady hand and a good soldering gun (25W min) could solder a known leak shut, with care taken to not solder the WHOLE tube shut. Others have suggested pulling the tube out of the bowl and replacing it, but finding one with that funny crimped top and tiny diameter, much less getting it in, would be nigh unto impossible. Best bet, if the overflow tube is the culprit, is to cast about here or on the 'bay for a replacement.

[Philly550K1]

i'm wondering why you've been needing new inline filters every month, and if whatever's filling them just happened to lodge in that float valve after craftily hiding out somewhere else in the meantime....

[dusterdude]

hymy,like i said,my pipes are cracked on three of the four carbs.i jb welded them but they still leak a bit.i ran clear battery overflow hose off the nipples to a point above the carbs and have not had any problems with this solution so far.also,im not leaking gas into the engine or the oil too.

[Bob Wessner]

i ran clear battery overflow hose off the nipples to a point above the carbs...

I'm trying to picture this solution. If I understand it correctly, doesn't the correct configuration of the overflow tubes provide an outlet for too much fuel, whereas your solution risks excess fuel having to go either to the airbox or engine if the float valves fail or get stuck??