need float hight #'s having problem with 81 750ltd

well my cherry 750 isnt so cherry :laugh: after taking it for a ride the other day i discovered it was not running on the #1 cyl, well the culprit turned out to be the float was in it upside down and whoever done it also had the float needle clipped in wrong. i put everything in right but now gas leaks out of the bottom of float bowl, i checked to make sure the rubber and the float bowl drain screw were good and they are. im thinking the float hight might be wrong and causing gas to drain thru the brass vent attached to the float bowl. the bike runs fine but drips gas constantly.

Hmmm.... I would think if the fuel level was high enough to drain gas out the overflow constantly, the bike would run like crap. Mine wouldn't run right with one float set about 1mm to rich for fuel level.

Anyway, I think your bike has Mikuni BS-38's and the correct fuel level for those is 4.5 - 6.5mm below the lower edge of the carburetor body (just above the bowl). You measure it using the clear tube method and adjust by bending the tang on the middle of the float.

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One common cause for fuel overflow is where the float needle/seat interface isn't correctly seating, due to crud or grit, or worn parts, or possibly a damaged or sticking float, or upside-down assembly of float, or other mis-assembly.

Another cause, as bountyhunter suggested, is a too high float level setting.

And here's yet another possible cause.
Some carb overflow circuits include a small brass tube inside which sticks up from the bottom of the floatbowl.

The tube has a hole through its centerline whereby fuel rising high enough is allowed to escape through the tube and flow through an outlet nipple located on exterior bottom of bowl. Typically, a rubber hose attached to the nipple directs escaping fuel over the swingarm to drip out underneath the bike.

A possible source of leaking fuel is sometimes a crack in the tube or a break where the tube connects to the floatbowl floor. The crack may be small and difficult to detect. But it's easy enough to test integrity of the tube with the floatbowl removed and in hand. Just fill the bowl with fuel (or common rubbing alcohol for a more pleasant odor) almost to top of the tube, and see if there's any leakage from the nipple. Not supposed to be any leakage. But will leak if the tube is cracked.

Just something to check out, especially where satisfied that the float needle/seat interface is clean and correctly seating and that the float level is set to specs, and parts correctly assembled.

Good Luck!

bountyhunter wrote:

Hmmm.... I would think if the fuel level was high enough to drain gas out the overflow constantly, the bike would run like crap. Mine wouldn't run right with one float set about 1mm to rich for fuel level.

Anyway, I think your bike has Mikuni BS-38's and the correct fuel level for those is 4.5 - 6.5mm below the lower edge of the carburetor body (just above the bowl). You measure it using the clear tube method and adjust by bending the tang on the middle of the float.

ok, what is the clear tube method

Get a clear fuel line and attach it to the bowl drain. You may need a nipple in the end or if the tube is the right size you can jam it in the drain screw. Some carbs have the drain port already and you can just slide the tube on. Make marks on the tube, mark them at whatever the fuel service level happens to be, ex. 3-5mm fuel level. Hold the tube as pictured so the top mark is at the bowl/body junction and adjust the float until the fuel level sits at the proper mark.

pic 2

Where carb has both a drain screw and a separate overflow nipple, be sure to use the drain screw hole when checking the fuel level.

Typically, the drain screw is side-located on lower part of float bowl, and overflow nipple is from bottom of float bowl.

Am uncertain, but thinking some carbs have a combo drain/overflow nipple which may be used for the clear tube test.

Good Luck!

On mine, the overflow nipple couldn't work because the fuel can't get into it under normal levels. The drain screw hole is definitely the right place to connect the bottom of the clear tube.

Patton wrote:

Where carb has both a drain screw and a separate overflow nipple, be sure to use the drain screw hole when checking the fuel level.

Typically, the drain screw is side-located on lower part of float bowl, and overflow nipple is from bottom of float bowl.

Am uncertain, but thinking some carbs have a combo drain/overflow nipple which may be used for the clear tube test.

Good Luck!

man you guys are awsome, mine does have the brass colored rod that runs from the bottom of the float bowl up so im thinking that i will want to use the drain screw hole right? i went ahead and ordered a float needle just in case. my next step is to find some tubing, im hoping some of my r/c airplane stuff will work, iv got all kinds of fuel line tubing & what not. its weird to, this thing didnt drip right at 1st when i flipped the float and installed the needle right, it gradually got worse and worse. im confused to where the gas is coming from, because the pet-cock is working but it keeps filling my little cup i have under it. im wondering if the float needle isnt shot from the float being upside down and the float needle crammed into the seat when the float bowl was installed

Check to see if the bowl gasket got damaged from removing the bowl multiple times. Sometimes they leak and sometimes they don't after reassembly.

cott10r wrote:

...ordered a float needle just in case. my next step is to find some tubing...didnt drip right at 1st when i flipped the float and installed the needle right, it gradually got worse and worse. im confused to where the gas is coming from, because the pet-cock is working but it keeps filling my little cup i have under it. im wondering if the float needle isnt shot from the float being upside down and the float needle crammed into the seat when the float bowl was installed

Thinking probably need to stop constant fuel dripping from #1 carb before doing the clear tube test or any float level adjustment.

Not strongly suspecting damage to float needle tip due to upside down float. Thinking more likely the float adjustment tang might have bent out of position, but just guessing.

If not already done, would fit an in-line fuel filter to help avoid future crud/grit in the float needle/seat interface.

Exactly where is the little cup located? Is it sitting on the floor underneath the bike catching fuel dripping from the overflow tube, or sitting under the petcock or under the carb floatbowl or somewhere else?

Perhaps a fuel line connection is leaking, or leaking fuel pipe (tee-joint fitting) between inner carbs, or fuel joint between #1/2 or #3/4 carbs, or crack in fuel line? Or maybe the bowl gasket is leaking as suggested by Kawickrice.

Good Luck!

i have a little plastic dish thingy sitting directly under the #1 carb float bowl. this bike is weird, because supposidly these carbs were freshly gone thru then sync'd, i think the guy flat out lied imo, how could anybody sync a bike with a dead cylinder? i think it might of been a mid-90's restore that ended up sitting along time