Topic: 500K1 carb overflow troubleshooting

[AndyH]

When I bought the 500K1 cafe racer several months back, it came with an annoying leak from the overflow tube on carb #2.
It did this whether the petcock was on or off, which had me a tad perplexed.  Anyway, I eventually tracked half of the problem to hardened fibre washers on the M6 screws fixing the petcock to the tank.

Having solved this, I proceeded with my restoration ( see here. )

I'm now pretty close to completion and took the bike for a ride or two without drama a few days back.

Mindful of the other half of the problem (#2 o'flow leakage with petcock on) I left the petcock on for a few days with a small container under the overflow tubes of all 4 carbs. During this time I thought I'd do a quick clear tube check of the carbs.  1,3 and 4 were all 2-3mm below the bowl face but 2 was ~6mm below.  At this stage there was no sign of leakage and I left the clear tube connected to #2 overnight.  Level the same, and still no leakage.  I removed the clear tube setup and replaced the plug.

This morning, I turned the petcock off for a while, came in later and turned it back on.  Within an hour or so, ~15ml of fuel had drained from the #2 bowl! 

Because this leak is NOT a regular thing, I'm a bit puzzled as to what the cause may be.
I'm thinking either an overflow tube crack, or a problem with the float needle (I'm leaning towards the latter).

I have no details of any work that was done to the carbs prior to my purchase, but suspect very little as the drain plugs were full of hard gunge (an Australian term  ) which I subsequently cleaned out, and the o-rings were crap (which I replaced)!

Regardless of the above, I reckon I'll probably have to pull the carbs and give them a damn good going over!!

What say you, oh masters of the carb overflow sagas and solutions? 

[Deltarider]

Before doing what you suggested, I'd do this first:
1. Tap against the floatchamber with the stub end of a screwdriver
2. Remove drain screw of carb #2 and with container underneath open and close the petcock a couple of times and see if you can flush out any debris.
3. Add a fuel additive to the gas in your tank like Tunap, Forté, Bardahl or Seafoam and... ride.
If all this doesn't help, remove floatchamber #1 and #2. Clean or polish #2s floatneedle, seat and swivelpin with a very little toothpaste or whatever. Swap floatbowl #1 and #2 as Calj said.

[AndyH]

Thanks guys, I'll try all the above.

[tlbranth]

If the problem doesn't surface from any of the above, check for a dimple on the float tang. It'll cause the float to stick.

[strynboen]

is the fuel tank komplet klean for rust and dirt21

[AndyH]

If the problem doesn't surface from any of the above, check for a dimple on the float tang. It'll cause the float to stick.

Duly noted.

is the fuel tank komplet klean for rust and dirt21

The tank is in pristine condition mate.  Just one carb playing up.

[jonda500]

I'll have a guess- maybe the PO fluke-ed a temporary cure to the leak by bending up #2 float tang - in my experience this wouldn't work if a worn needle & seat was the cause of the leak, so I'm guessing it's probably a dimple in the float tang that's causing it?
John

[AndyH]

Before you panic, swap the bowls on 1&2 and see if the problem follows. If so, you have a cracked tube. If not, likely its the float valve/seat. Then you can wince about your repair 

Swapped bowls, #2 still leaks.

Before doing what you suggested, I'd do this first:
1. Tap against the floatchamber with the stub end of a screwdriver
2. Remove drain screw of carb #2 and with container underneath open and close the petcock a couple of times and see if you can flush out any debris.
3. Add a fuel additive to the gas in your tank like Tunap, Forté, Bardahl or Seafoam and... ride.
If all this doesn't help, remove floatchamber #1 and #2. Clean or polish #2s floatneedle, seat and swivelpin with a very little toothpaste or whatever. Swap floatbowl #1 and #2 as Calj said.

Did 1 and 2 before swapping bowls DR.  Interestingly, there were a few tiny black specks in the drained fuel.  Several drain sequences did NOT result in clear fuel...   This debris didn't originate from the tank because I drained #1 a couple of times with clean fuel coming out.

I'll have a guess- maybe the PO fluke-ed a temporary cure to the leak by bending up #2 float tang - in my experience this wouldn't work if a worn needle & seat was the cause of the leak, so I'm guessing it's probably a dimple in the float tang that's causing it?
John

Either this, or sticking float needle.
While the bowls were off I checked the slow and main jets: they were 40 and 100 respectively but definitely aftermarket.

As the leak occurs only when petcock left on for a long period, I'll continue to ride till my SOHC restorer mate returns from NW WA (Western Australia that is!  ) in a couple of weeks and then we'll pull the carbs and give them a good cleanout etc.

[Deltarider]

It takes just a eeny, tiny speck to prevent the floatneedle to fully close. I'd use an additive. It did a miracle for me. Modern gasolines seem less lubricous than in the 70s but... that may be my imagination to be honest. 

[tlbranth]

swap just the float on #2 with another. If the problem moves, it's probably a tang dimple.

[TwoTired]

One source for bowl specks, apart from tank and fuel lines, are the vent hoses.

Insects like to deposit debris in those, as they are open ended.  Its a direct path to the float bowls.

Cheers,