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Tillotson carb adjustment


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Just went through my poor "A" model...it had been sitting for 4 or 5 years since I last started/ran it. I lubricated all the grease fittings, changed the oil, checked the timing, points, spark gap, put a little oil in each cylinder, turned it over by hand several turns. Pumped up all of the tires, topped off the transmission, steering box and rear end with 600w oil, drained what little dead gas there was (pint at most), and sprayed some carb cleaner in the gas inlet port of the carb. I did not dismantle the Tillotson carb. My questions are; how many turns open do you set the choke rod adjustment and how many turns open do you set the idle/run adjustment (horizontal screw above bowl going into throat area?

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Each Model A is different regarding where they like their choke rod adjustment (rotating this left and right adjusts the air-fuel mixture) and their idle adjustment. For a Tillotson carburetor that is in good operating condition, you should start be opening both of these about two full turns open-meaning screw both down as far as they will go (but do not force) and open them both two full turns. That should get you a decent setting to get the car started since it is cold and hasn't run in awhile. Once the car starts, advance the timing to about 1/2 down the quadrant let the car get warm. Now, you can start screwing the choke rod adjustment down until the car starts to starve for gas and then back it out about 1/4 of a turn until it recovers and runs smooth. Typically, these carburetors run best at about 1 to 1 1/4 turns open when the engine is warm and 1 1/2 turns open when cold or starting cold. Once this is adjusted, slow the engine speed down and go to the idle adjustment screw on the carburetor. Again, start turning it down until the engine runs rough and then open it up again until it smooths out. You'll probably end up with this screw being run about 1 1/2 turns open for good idle. Remember, all Model As have different "sweet spots" for carburetor adjustments, so these settings are just approximate. You'll figure out what works best for your car by trial and error. Also, you'll need to be sure you're timing is set right before you can accurately dial in the carburetor. Good luck and let us know if you have any other questions.

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For a rebuilt Model X Tillotson carb (using new gaskets, needles, etc.) they recommend the following;

"First: Before starting the engine, close the low speed adjustment to its seat, then open 3/4 of one turn.

Second: Close the high speed adjustment on the dash, and open one full turn.

Third: Start the engine and run the engine until thoroughly warm.

Fourth: Close throttle and retard spark fully.(Be sure the idling screw on throttle lever is set to run the engine at a driving speed of     six to seven miles per hour). 

Fifth: Very slowly turn the low speed (idling) thumb screw to the left or out until engine flutters or misses. When this point is found turn to the right until motor fires evenly.

Sixth: It is necessary for the driver to determine the best position of the dash or high speed adjustment. Usually with a warm motor the best running adjustment will be from 1/8 to 1/4 turn open. To make the best adjustment it was recommended to run the auto at 25 mph with advanced spark and set the adjustment so the engine runs smoothly without missing or surging."

     Hope this helps, I just did this to my '29. The info came with the rebuild kit. Good luck!

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Motoringicons....Caddyshack..................Thanks, cranked the beast up today...backfired a little at first then evened out ...let her run for a while with the gas up, spark retarted .....slowly eased off the gas and cut back on the spark retard...she leveled out as the carb rid itself of gunk from the dead gas...

Edited by HarryJ (see edit history)
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  • 1 year later...

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