I have a 1947 Ford Tudor, it’s running a twin 97 setup on a Thickstun PM7 manifold, Offy heads and standard Crab ignition. My spark plugs are fouling and get real sooty and black. It looks to be over fueling My question is what size jets should I be using in the carbs? Sent from my iPhone using The H.A.M.B. mobile app
Yea, wrong title... "Carburetion issue". Could be too high a float level, could be a too high a fuel pressure, along with too large a jet. Verify your idle mixture screw location also. Have you balanced the carburetors yet ? If one is too much farther open or closed than the other, that'll screw with the...other carburetors action. Mike
Start with the standard jets, off the top of my leaky head that is .045. They should work fine, SMALL change MIGHT be better but that's not a concern until car is running pretty well. If you are using small chrome type filters, take them off and tune car. Those things flow about right for a lawnmower, and act as CHOKES and will destroy your piston rings from all the gas wash. I'm betting on them as the prob. Also, read the VERY easy stock timing adjustment for the crab. Retarded timing mimics over rich. As a minimum timing scale should be about at center or a bit advanced...again, don't experiment with it until car is running pretty well. The little chrome filters can be be improved by hammering them flat and reinstalling them under the spare tire.
Here's timing. You need 2 rulers, and a few minutes to figure out rotation and up and down...a bit confusing once it's off the engine, a five minute job the second time you do it. Remember left point means driver's side, no matter how you hold it. I actually mark right and left, direction of rotation, and advance-retard on scale with a Sharpy to prevent stupid errors then hose it clean with spray carb cleaner when done. I find that it's easy to get lost once the thing is off the engine and upside down and backward...
I agree with Lancaster on jet size to start but black plugs can also mean spark strength. Check voltages at plugs and at coil/condenser. If you have a big resistor check that. Sent from my SM-J727V using The H.A.M.B. mobile app
If the issue is carburetor: Stromberg 97's as built from 1936~1938 by Stromberg USA used 0.045 jets. Factory service 97's built from 1939~about 1947 used 0.046. I have no clue what is used in the modern repro carbs. Stromberg 97's like about 2.5~3 psi fuel pressure. Would check this first, especially if an electric pump has been installed. More than 3.5 psi will cause rich running. I will defer to others on ignition, etc. Jon.
I had the same intake on my 59Ab and ran .043 jets and #67 power valves. Burned perfectly brown and ran strong. Sent from my SM-G955U using The H.A.M.B. mobile app
Plugs are black after a shirt run about 5 miles to test it and they were black Sent from my iPhone using The H.A.M.B. mobile app
This is definitely where to start. Maybe he knows this stuff already, though maybe not. The fuel height in the bowl has to be within a certain range, not too high, not too low, or it will tend to run too rich or too lean. The main well is going to seek the same height as in the bowl as I understand it. The exact level is a part of the carb calibration. It affects how much fuel is pulled by the different air bleeds and atomization. The pic shows a different carb than under discussion but you get the general idea. Too much or too little fuel pump pressure causes trouble, and the float height in turn also affects the fuel height. Somebody once said if you could only get one carb adjustment right, fuel height would be it. When you know for a fact that fuel pump pressure & fuel height is OK, then proceed on with jetting &c.
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