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carb overflow mystery

  • Thread starter Thread starter wompin
  • Start date Start date
...it's tricky alright,wompin, because your carbs are linked with an overflow tube?my twin carbs for two cylinder engine are..I have to guess that 4 cylinder bikes are too (in pairs?) without looking them up

-so, it easily could just be one bad carb needle seating whether float or actual needle... just possibly a bit of valve-grinding compound betwixt needle and seat might do fix a needle issue in a pinch. but buying new certainly crosses stuff off the list alright...the only float-needles I've personally had lots of issues with are rubber tipped ones...needle seats?-well more troubles,yes...but I don't do all that much mechanikking compared to others here so i haven't got a statistical sample :)

PS:Idea: I really have doubts your floats are not buoyant enough if they came with the carb! You can rattle em and see if there's a leak in em, otherwise, what's to go wrong?except the bend in the little tab AND JUST POSSIBLY the tiny springs on the needles, if you have these.. if the needle and seat are good, the floats will hold back more than a full tank...(unless of course the tank vent was plugged and the tank warmed up...)
Check that- your bike might (like mine) have the little spring-loaded stem on the float needles at the float end ..Do yours?... Took me awhile to notice I had these. IF THESE JAM YOUR BOWL MIGHT VERY WELL OVERFLOW.
 
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Yes the needles do have springs and they seem to be intact and functioning well. I looked at my floats and they seem fine. My petcock is fine.

Im fairly certain my valve assemblies are at fault. The needles are steel and the seats are brass. I cant seem to find them any cheaper than 15 a piece plus shipping = $70+. I think Ill try some valve lapping before I bend over to that price.

If anyone knows what mikuni or K&L part number I need for the float valve assemblies for mikuni VM26ss carbs, that would help.

I know they are Mikuni part number VM26/26 but there is a choice of 1.5, 2.0, 2.5, or 2.8 (whatever that means). Im not sure if K&L sells the valves seperately or not.
 
Valve lapping won't work. Or if it does it won't work for long. Replace, replace, replace
 
..you mean by "valves" the float needle+seat? I hope you are sure you have found the problem before spending $$...get that drip happening with the carb in front of you, for sure...it's worth it to really know the cash is doing it's job or it's a long wait for delivery and a big downer at the end of it....it's likely just one needle+seat b*ggered and that would save $.
otherwise, I'm scraping the bottom of my imagination, but would shifting needles carb-to-carb help? (keeping em paired if the carbs were) I'd be marking these so I can put them back where they came from, but I wonder if you mixed them up on a dissassembly?
 
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Yeah lapping does sound kind of stupid now that i think about it.

I totally agree, I want to SEE the problem before I try to solve it. So... I guess I need to pull the air box and carbs aaaagain. I tried to just clamp a hose onto the individual float valve seats while off the carb body and see if I could reproduce the leak - no luck, it doesnt leak. yet it does.

I cant confirm that the needles and seats stayed together so I will assume they are mixed up, which sucks since there are 16 possible arrangements of the float vavles.
 
"...it doesn't leak yet it does" and you saw this leak Where? under the bike? gotta isolate it better than that...it might be just a crummy hose, you know.
Stop pulling things until you have to. If you have it all pulled, well, that's ok because you can be sure by running a "petroleum distillate " to each carb separately...
on the bike, you just have to track it back with a bit of toilet paper,your finger etc. or just a bright light and wiping where it is. You'll often see the leak "filming" over the metal even before it build to a drip.
If the tank is in the way, make a little one up from a lawnmower or the like. Even a funnel that fits the fuel hose.
and,in the very end, there's the " little brother" syndrome ( or April Fools) when it never drips for you but only after youre gone ...he could be sneaking in and dribbling some on the shop floor ....:)
(a bit of fine lapping compound can polish corrosion off -I'm not suggesting a valve grind! and it doesn't always work- a last chance maneuver for sure)
 
Wompin, You have an L model bike. Your petcock has two settings: PRI and on. There is no OFF setting. If you have it on PRI, your carbs will probably overflow, on the sidestand especially, and it would be the lower two.
 
DanTheMan said:
Wompin, You have an L model bike. Your petcock has two settings: PRI and on. There is no OFF setting. If you have it on PRI, your carbs will probably overflow, on the sidestand especially, and it would be the lower two.
Click to expand...


Apparently I have a non stock petcock, because there is no prime position. There is only reserve and fuel. Both are "on". It is a vacuum petcock so the spring on the diaphram is the shuts the fuel off.

I am considering purchasing a manual on/off petcock (universal with adapter plate) for peace of mind.
 
DanTheMan said:
Wompin, You have an L model bike. Your petcock has two settings: PRI and on. There is no OFF setting. If you have it on PRI, your carbs will probably overflow, on the sidestand especially, and it would be the lower two.
Click to expand...
Just because it's an "L" does not necessarily mean that there are only two positions. :-k

I just looked at the parts fiche, his petcock looks a lot like the one on my wife's bike, and I know for a fact that it has RUN, RES and PRI.
icon_shrug.gif


You may be confusing that with the "dreaded '80 petcock", which had only RUN and PRI, but no RES. :-\\\

Fortunately, only the '80 bikes had that dreaded item, even MORE fortunately, not all of the '80 bikes had it. The non-L shafties were spared. :dancing:


.
 
Steve said:
Just because it's an "L" does not necessarily mean that there are only two positions. :-k

I just looked at the parts fiche, his petcock looks a lot like the one on my wife's bike, and I know for a fact that it has RUN, RES and PRI.
icon_shrug.gif


You may be confusing that with the "dreaded '80 petcock", which had only RUN and PRI, but no RES. :-\\\

Fortunately, only the '80 bikes had that dreaded item, even MORE fortunately, not all of the '80 bikes had it. The non-L shafties were spared. :dancing:


.
Click to expand...
I thought the L bikes were all afflicted with that until '81. My bad.:o
 
The "on/off" ones don't necessarily give you peace of mind especially when you forget to turn them off...
 
Good point cowboy. I guess then if/when it overflows at least Ill know which part is defective (that being my fading attention span ofcourse).
 
wompin said:
Im not sure I know what youre asking, but the gas goes in the center inlet "T" on the carb bank, through the carb passages and past the gas inlet valve. This is where the leak is occurring. Then, obviously, my bowls fill to the height of the overflow pipe, and out the overflow tubes onto the floor. My guess is this is not what you are asking since this info is obvious
Click to expand...


i would like to SEE where the gas is leaking from exactly..

is it the overflow hoses or is it

THE VENT HOSES// there is a difference.
 
The "leak" is internal. Gas is "leaking" past the float valve since the valve is not stopping the bowls from overfilling. Consequently the gas then flows through the overflow tubes as designed.
 
Did you ever figure out the culprit? A bad valve and valve seat perhaps? I'm having the same issue, just rebuilt all carbs with new o-rings, valves and seats seamed fine. I set the float height properly, but it still is leaking.

I have a hope that it is the tank vent. I'll be checking that tonight.
 
Freebeer said:
Did you ever figure out the culprit? A bad valve and valve seat perhaps? I'm having the same issue, just rebuilt all carbs with new o-rings, valves and seats seamed fine. I set the float height properly, but it still is leaking.

I have a hope that it is the tank vent. I'll be checking that tonight.
Click to expand...

I had my carbs off just the other day for probably the fourth time. I set them up with a temp fuel tank. They held back fuel but the level in the clear fuel line would drop about 1" per hour. There was no accumulation of fuel on the floor like there was during earlier trials, though. I cleaned and polished the needles and seats, but got same result. I have concluded that the 1"/hr drop must have been due to evaporation of fuel.

I did buy new needle/seat valves all around just to be sure. No leaks. Im pretty sure the issue all along has been bits of rust and/or debris getting in between the needle and seat. Most likely my other needles/seats are fine. They show no signs of wear, anyways.
 
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