41 V12 Runs poorly

[Guest imported_48DLX]

My friend has a V12 that lacks power, runs very poorly. He has had some work done on it in the past but it it still does not run well. It seems to be running rich, you can start the car after it has sat overnight without any choke! If you stop it you can 't give it any gas or it will flood. What would cause this? I am going to check carb, would a float adjustment help this? I see in another post there is a power valve in this carb, what is that a accel pump sort of thing? I tried to take it for a run today, it just won't go, I had a hard time getting it over 20 mph!!! UGH!! Thanks, Dave

[peecher]

The float valve could be leaking and or the float level is set too high but most likely the power/economizer valve is leaking and dumping gas directly into the engine. The material in the old power valves does not like modern gas. When you remove the base from the body see if there is dampness(gas) in the cavity of the base directly below the power valve, a sure sign the power valve is leaking. Be sure to check the bottom of the bowl for "flatness" as any vacuum leak between it and the throttle base will also cause the carb to run rich even with a new valve.

These old Holleys warp with age and you either need to true up the bottom of the bowl with a file(if you're good at it) or have the bottom milled flat. You must also check the surface of the throttle body that mates to the bottom of the bowl as they too sometimes warp a slight amount.

Check the carb carefully for "loose" components like the nozzle bars or missing components like the valve under the accelerator nozzle. Unbelieveable what you sometimes find when you take one of these apart! Modern carb kits have components that don't deteriorate with modern gas.

When fixed right these carbs are absolutely bullit-proof and give good trouble-free service.

The accelerator pump only pumps a small amount gas when the throttle is moved ( to open) but does not pump any gas at steady throttle. The center (#2) position on the throttle arm is probably the best position for the link unless you're in some extreme temperature.

[carbking]

Peecher's post is excellent; however, I would add one caviat:

The power/economiser valve in these carbs is a diaphragm, and, as mentioned by Peecher, located in the bottom of the bowl. JUST ONE backfire through the carburetor is normally sufficient to kill this valve; thus allowing the carburetor to drain directly into the engine. Thus, it is imperative that the ignition system and timing is in good shape.

Other than this flaw, the carbs are fairly reliable.

Jon.