BLACK BUILD-UP ON THE SPARK PLUGS AND OUT OF THE EXHAUST

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I Have a 1929 Model 133 straight 8 and the spark plus build up with a lot of black (almost like power) I have to clean them about every other time I drive the car. Of course it also blows (black power like) out of the exhaust. I have read I should run with the spark less advanced but then the cars seems to have less power. Can anyone recommend anything? Other then that its starts and drive just fine. FYI, I did install a newly rebuilt carb about a year ago and thats when this started.

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The short answer is that your carburetor is most likely not jetted correctly, and you’re running a very rich air/fuel mixture.

I’m sure the better mechanics will jump in! But the clues you mention sure point to a carb problem…

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There are several tings that can cause too rich a mixture. One is just plain starting and stopping the engine for very short periods without it warming up. Just running it long enough to move it in our out of the garage or around the block instead of driving several miles will build the carbon up.

Another is the choke pulled partially closed or misadjusted. It should be wide open after the engine is warmed up. Another is running without a thermostat (if equipped) or the radiator shutters (if equipped with temperature controlled shutters)are forced open. These items keep the engine from ever warming up in cool temperatures or extend the time it takes to warm up in hot temperatures. I was constantly fouling plugs on a car that I liked to drive around before I had the grille shutters installed that let it warm up.

Carburetor float level too high or float leaking and sinking, or float valve not sealing. Fuel pressure from an auxiliary electric fuel pump too high and overpowering the float valve.

I would check these things before carb jets.

Good luck, Jim

Jim

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Both my 1601 and 1247 have been re-jetted to a larger opening to provide more fuel and they run VERY much better at some expense to fuel mileage. I doubt that being jetted too rich will be a problem. I use inline thermostats rather than the shutter system since we only drive in the summer here in the Midwest.

I suspect that Jim’s first suggestion is the most likely culprit. Short run times or long idling will cause carbon buildup. Get the car out on the road and run at highway speed for an hour…if we are lucky enough to get another decent weather day before Spring. These big Eights don’t need nor like to be babied. I remember when I began driving in the 1950’s it was common for most cars to benefit from a higher speed drive to ” burn out the carbon”” and I regularly still do it myself on all of our pre-mid 1950’s.

The best 1929 experts in our Region are Bill Morris & Greg Long.

Dave”

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The standard jet plug size for a UU2 for ’29 Pierce is .046. This jet is located at the bottom of the float chamber and is removed from the outside as it has a 7/16 hex head (I think). The original jets have the size stamped into the hex head.

I would verify what jet you have and also verify that the choke opens fully when you push in the dash cable button. Also verify that the float does not have a leak in it and that the float level is correct.

Bill

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More often than not, (80 percent of the time) the car has an incorrect carburetor on it, swapped out over the years. Too much fuel pressure, stuck choke, wrong jets, I wouldn’t assume automatically that it is fuel, I would also think oil issues. To load up the motor so bad you need to swap out the plugs so often, I would start with the basics, put the car on a five gas exhaust analyzer, you will get your answer.

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I recommend a compression test for all cylinders then confirm ignition in not missing or weak (eds suggestion) then if all clear, check carb per all of the above.

All three are potential culprits.

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Sorry one more item to add, but this come from total ignorance on ’29 carburetors. If there is a “power booster” or “economizer” valve that opens at high throttle – it possibly could be stuck open or otherwise messed up or misadjusted. That valve opens to richen the mixture quite significantly on the order of 10/1 air/fuel for maximum power. That is rich enough to generate soot but the car would run smoothly without any obvious problems like missing.

Unless everything is just plain worn evenly, I would expect broken oil rings or stuck compression rings passing oil to leave plugs with much bigger buildups on some but not others. The buildup on the plugs would probably be uneven compared to rich mixture that would be evenly deposited and more powdery looking.

Burning oil exhaust tends to be a bit blue rather than pure black. As long as the engine is firing evenly ignition advance or retard is a weak influence. If the car is running smoothly without any misses and the exhaust is black, it is most likely rich mixture.

Jim

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Hello Steven, when you say the cat start and runs just fine, why do you have to clean the spark plugs so often?

Does the engine start to miss and runs poorly until the plugs are cleaned?

Do ALL the spark plugs get equally contaminated? Are any of the plugs damp or wet looking along with being black?

Since this problem arrived with the installation of a ‘rebuilt’ carburetor, that sure sounds like the most likely culprit. But it could be that during the installation of the new carb, that maybe the choke cable was not hooked up correctly, and the choke plate is not opening fully.

When do you see the black sooty exhaust? When the engine is fully warmed up, and idling? or when accelerating? or ??

I would suggest you pull your engine oil dipstick, and look at the oil level,and smell the oil.. if it smells like gasoline, and the oil is thin or watery, and especially if the oil level is high, then you are getting unburnt gasoline running past the piston rings and it’s diluting the engine oil which is a very dangerous thing that will eventually result in an engine failure with ruined bearings.. Change the oil soon if the oil is diluted.

Please give us an update on what you have checked, tried or discovered.

Greg Long

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Hi Steven,

Do you have any update on the running condition of your car, and if you found any reason yet for the sooty spark plugs?

Greg

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