Bruce:
I am not sure what the original equipment carburetor was on the 78
New Yorker but I believe it was a Carter Thermo Quad. If you replaced
it with a Thermo Quad and the rest of the engine (valves, plugs, plug wires,
etc) are in good condition you should be able to get the car to idle and
run well when it is warmed up. The weakness on these cars was warm
up driveability. They did not do well just after starting (the second time)
and during warm up. You just have to live with this.
There are a few critical areas you should check if you have a Thermo
Quad carburetor. These did need periodic maintenance. Maybe once
every two years they had to be gone over.
I would not remove any of the anti-pollution devices assuming they are
correct and operating properly. Also I doubt that the exhaust leaks are
causing much if any of the problem.
First I would check to be sure the timing is near 8 degrees BTDC. Then
I would check the carburetor float level. With the air horn inverted the
distance from the gasket to the bottom of the float should be 29/32.
I would then readjust the engine idle speed to 750 rpm. This is the
correct specification but may seem a little fast since most engines
idle between 550 and 650 rpm. Then I would adjust the idle mixture
screws one at a time (I expect you will have to force the plastic caps
off to get at the screw) until you get the smoothest idle. You may
have to readjust the idle speed.
Finally I would adjust the secondary air valve spring. This may be causing
the stumble when you floor it with no load. You should get a carburetor
book to find the air valve adjustment plug so you can remove it and get
at the spring adjustment. Turn the spring adjusting screw with a screw
driver until the valve just closes then turn it 1 1/4 turns more.
These are the critical adjustments on this carburetor. If it is a TQ
you should be able to get it to run smooth and perform well when the
engine is warm.
Good luck.
Rolland Westra
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