My ‘49 Commodore eight is percolating fuel in the carburetor bowl and I’m suspecting the culprit is a stuck heat riser. The carb has been rebuilt, has a stack of four paper gaskets below and another four above the heat shield, stainless fuel line is routed away from the exhaust, fuel pump has phenolic bolt sleeves and stack of paper gaskets between block and pump. After a good thirty minute run, the carb becomes quite hot, too hot to hold your hand on and fuel is visibly bubbling in the glass filter bowl. Oddly enough the engine runs well enough though is obviously running a bit rich.
Without removing everything, how can I tell what position the heat riser is in? It does not change position from dead cold to hot regardless of engine speed. Has anyone had success with freeing the valve without removing the manifold? Is it even worth repairing or should I just remove the whole assembly?
Jake, there should be a cotter pin at the top of the shaft, it's a very small pin, about 3/32nd's. That pin should be parallel with the manifold when the heat riser flap is open. If you use a pair of channel locks to turn it clockwise to open. Do you have an infered temperature gun?. This is a very handy tool to help diagnose the concern. You can also check the radiator temp with this tool and determine if you have good circulation thru the block and radiator, closely inspecting the water jacket as well.
Thank you Doug! The pin is perpendicular to the manifold and block so I’ll have to attempt to free it up. I’ll try the IR thermometer tip as well.
I just last week removed the heat valve from the manifold of a '36 H8. Heated the nuts to a cherry red, and after cooled, used vice grips back and forth on the nuts until they freed, and removed. Then tapped the body of the riser with hammer and blunt chisel until it came loose, also tapping the bottom of the shaft. This enabled me to remove the unit. I cleaned the valve up, and the inner top of the riser, and welded into the open position with a blob of stainless arc electrode. This was all done with the manifold off the block. Alternatively, you could remove it altogether, and replace it with a bolt and nut through the hole at the bottom, and a steel plate over the opening in the manifold.. With today's gas you do not need this valve. Also double the size of your heat deflector under the carburettor. Hope this helps,
Geoff
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