1959 Mark 6A Spits fuel

[blaseko]

I have a Mark 6A that spits fuel from the cylinder block bleed tube, not a lot but it appear to do it continually or least at low idle. Is this a carb issue or a reed issue or neither. What is the purpose of the bleed tube? The motor seems to run OK.

 

[Chinewalker]

Is that the overboard dump? If so, it may indicate you're running extra rich and puddling more fuel than normal in the crankcase. They weren't too concerned with the environmental aspect of dumping unburned fuel on the water back then. A decarbon to clean things up inside may help some as it may help increase crankcase and cylinder compression.

 

[blaseko]

Thanks for the insight, what do you mean by decarbon?

 

[Chinewalker]

There are mixes you can spray into your motor that loosen up old, built up carbon and flush it out. Carbon builds up on the piston domes, exhaust passages, rings, and ring grooves. Excessive carbon buildup can block off the exhaust side, rob compression due to stuck rings, and cause miss-fires due to hot spots on the piston dome. Sea Foam Deep Kreep, Yamaha Ring Free, Quicksilver Power Tune, etc. are available all over the place. Old motors like yours that grew up on a steady diet of old school, heavy ratios of 30-wt. are often found with considerable amounts of carbon inside, so it's a good thing to do, regardless.

 

[blaseko]

I tried to decarb with the Sea Foam as well as soaked and rebuilt the carb and installed new float with no change. In addition I recently bought a second mark 6A for a part motor for the first one and that started easily but also spit fuel. I wonder given the age and the fact that they seem to run OK that the diaphram from the fuel pump is leaking into the cylinder block?? There aren't many ways for fuel to get to the where the bleeder tube is??