Topic: Carb overflow

[derelicte]

Hi all,

I was attempting to vac sync the carbs tonight and 1 & 2 both overflowed on me.  Does it matter how high the tank is positioned?  The base of the fuel tank was about 1.5ft or so above the carbs - was wondering if that was just too much pressure for the float valve or something.  Also, the parts store only had 7/32 fuel line, so I ran that to the first carb inlet and my stock 5.5mm line to the second.  Logically it would seem the line might be overfueling it somehow, but isn't the 7/32 supposed to be fine?  It was still a press fit onto the barbs, no clamps needed...  Just wanted to check before I waste the time and money on more of the correct diameter line.

Some background:

74 750.  Carbs cleaned, rebuilt and bench synced along with new OEM, NOS float valve assemblies.  Floats set to 26 from casting (not gasket).  Bike sat for a few years since rebuild (unexpected job change) - I just returned to town with a set of 341s finally.  I pulled the bowls to rejet to 105s and everything looked perfect, should not be sticking. 

[Bodi]

I use a small fuel can that hangs about 4' above the carbs when doing stuff like carb sync with the tank off. Float valve leakage has never been an issue. Maybe your float valves were already leaky and the pressure increase makes it noticeable? Did you stir up some crud in the tank when removing it, and bits have jammed in the float valves? Draining the bowls then letting them refill should wash away most such particles, some tapping of the bowls while they're refilling helps dislodge junk.
Fuel feed hose size is irrelevant until it's so small it can't flow enough fuel... that's awfully small when syncing carbs at low throttle. 7/32" is  5.556mm - this is not your problem.
If it was bone dry at the overflows before you raised the tank, float level was apparently not overly high - but did you set the levels? You can check them with a clear tube, adjustment is rather difficult with the rack in place. I have never had trouble setting the floats (rack in hand) as described in the shop manual, by eyeball measurement on a ruler or with a float gauge.

[derelicte]

Thanks for the input so far.  They looked pretty good, maybe even a little low? 





The tank was in the way so I didn't check 3 and 4 yet but neither are leaking. 

I started it up last night with the petcock off and it started right up no choke and idled nicely.

FWIW the overflows are now just dripping with the petcock open - last night it seemed like it was more or less pouring.

[Jnel]

Cal... good graphics.   Thats a keeper.  This coming up on my list of TTD when i get home.  Appreciate the drawing.

Sent from my SAMSUNG-SM-G935A using Tapatalk

[derelicte]

Could the valves be to blame somehow?  They were bought as a set and the packages were definitely 70s or 80s.  Wasn't much bounce on the springs when I was setting the floats (I did turn the rack sideways to actually set them).  Any input appreciated as I don't have any other ideas on why its just the first 2 carbs doing this.  I don't even see how the clear tube test could show them at the correct level and still have them overflow.

[derelicte]

Thank you!  TINY cracks on both.  Both bowls were drained down to the aluminum molding when I removed them.  I'd post a pic but apparently photobucket doesn't allow 3rd party hosting anymore.  JB or solder?