Mysterious Fuel Leak

[Detroit Diesel Man]

Hmm..how do I start this other than I have a fuel leak at the float bowls that I cant seem to get figured out...yeah a fuel leak seems easy enough to fix right?..uhhh no...the bike runs perfect..I have zero issues with its running ..starts right up runs strong and restrts before the engine even rotates 360deg...but the float bowls leak/seep fuel..closer to the fuel mixture screw from what I can see...ordered a set of bowl gaskets and pulled the carbs..rechecked float height and its perfect..clean the bowls and bodies again..install new gaskets and re-assembled..went for a ride..still the same thing..fuel seeping from the bowls...thought ok..screw this..made my own float bowl gaskets from fel-pro gasket material and went through the whole process again..same thing...pulled the carbs again..let the gaskets dry and sprayed them with hi-tack and re-assembled..still a seeping of fuel around the bowls..drain screws are dry..just where the bowl meets the carb..I'm pretty lost at this point..any ideas or tips would be great..I did go through and re-tighten and check the bowl screws again (allem head)..going on a hour ride 1 way tomorrow for easter so we'll see what happens...again..any ideas or thoughts would be appreciated!



DDM

[chuck hahn]

orings leaking from around the pilot screws?? One may be torn or detriorated..runs down and around the carb rims????

[chuck hahn]

Does it leak only when the engine is running? Have you dried it and let it sit to see if it leaks when not running? Unless the carb body or bowl is cracked, i cant think of any other place down there that fuel can seep out. You stated it isnt from the drains or overflow.. Maybe when its running and gas is passing thru the pilot circuit a small amount is seeping down and past the oring???

[Nessism]

You also might want to check the fuel level, not just measure float height. It's pretty easy to make your own gauge using some clear tubing and a screw that threads into the float bowl drain.

[Flyboy]

Did you check the levels on the bench or with the clear tube method on the bike while running?
I have heard more than one story on here where the levels all checked out perfect when measured on the bench, then when checked using a piece of clear tube on the bike while it is running, the floats were way out.
Also, maybe lay the float bowls on a piece of glass and check the mating surface for straightness, there may be a little warpage from all the years.
If so, put on your favorite DVD, a piece of glass, a sheet of fine sand paper and start correcting....................oh. and beer.

[Detroit Diesel Man]

Thanks for all the replies..I didnt check the fuel levels with a clear tube..but thats a good idea..I'll have to make up some ..the carbs had new o-rings last year but I guess it is possible they are leaking from the fuel mixture screw o-ring..I'll order a new set just to be safe..it does seem to seep when the bike ISNT running..wich made me think the fuel level as Nessim mentioned was off..I know the float height is on but maybe its possible the floats are a little "heavy" and checking fuel level I could adjust float height to compensate for that..hate to think what new floats would cost.....even if I could find them..now if I can just remember where I got my o-ring kit last year..somebody on here sells the correct orings I think...Thanks again for all the replies..lots to ponder and think about!


DDM

[rustybronco]

lots to ponder and think about!


DDM

http://www.cycleorings.com/

If you are measuring float height with the float just touching the needle valve, weak springs in the needle valve(s) will cause the fuel level(s) to be higher.

[BassCliff]

Hi,

Could it be worn float valve needles or seats? Were any parts replaced with an inferior quality "carb kits" and not OEM parts?


Thank you for your indulgence,

BassCliff

[Detroit Diesel Man]

http://www.cycleorings.com/

If you are measuring float height with the float just touching the needle valve, weak springs in the needle valve(s) will cause the fuel level(s) to be higher.

Thanks for the link!..I did find it and will order a new set of o-rings just because...also yeah I thought about the float height and possible wek springs in the needles..I measured the height with the carbs upside down with the floatresting on the needles...if the springs were weak I figured this would get me the closest to a accurate measurement..the springs seem good tho they do hold the float up and the float bounces back if you tap them and they bounce back. I'll be making a fuel level gauge tomorrow after I get back from dinner..dumb question but I assume I measure the fuel level in EACH carb and adjust accordingly?..list via cliffs website says the fuel level for my 77 750B should be 3mm below the base of the carb body..I'd be willing to bet that its higher than that and thats what is causing the fuel leak..so again I assume too low a a float level will cause the fuel level to be too high ( too low i mean with the carbs upside down)
meaning if the float level is set at 26mm and the fuel level is too high..I need to try the float height at 27mm. thus lowering the fuel level in the bowl...wow..if thats not confusing as hell..lol..thanks again for the link and reply!


DDM

[Detroit Diesel Man]

Hi,

Could it be worn float valve needles or seats? Were any parts replaced with an inferior quality "carb kits" and not OEM parts?


Thank you for your indulgence,

BassCliff

Originally I replaced the seats and the needles with stuff from Z1..but they were junk..aftermarket stuff..so I checked the needles under a magnifying glass and didnt see any sign of a wear ring...I put the stock needles back in and used the new seats...its weird..I ran the thing all last year and only had one leak from a piece of dirt in a needle..no float bowl issues...wich is why I am puzzled...I did find a source for oem mikuni needle and seats tho..at the rate of 38.00ea. still pondering that expense..thanks for the reply!


DDM

[rustybronco]

meaning if the float level is set at 26mm and the fuel level is too high..I need to try the float height at 27mm. thus lowering the fuel level in the bowl...wow..if thats not confusing as hell..lol..

Not confusing at all!

I did find a source for oem mikuni needle and seats tho..at the rate of 38.00ea. still pondering that expense...

Set the wet float level on each carb with what you have in it now.