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351C tune up settings
#1
I am having issue with my (wife's) car. It is a 71 M code, original intake, 4v heads exhaust manifolds stock as it could be made reasonably. It is equipped with a 600cfm oem replacement holley carb, purchased new when I did the motor back in 2005/6. Car sat for more than 12 years lonely in back of the garage, until last year, put a gas tank in it, and got it on the road. I drove it just over 25 miles before a coolant leak developed from the head gasket. Pulled the heads off, sent them out for evaluation/rework. $1200 later back together just in time to burry it in the back corner of the garage for winter. In that 25 miles, it ran ok, started well, but had a hesitation upon initial acceleration.


Its spring again here, aside from the snow we got on Saturday. I put a replacement radiator in as the old one was found leaking during the head work. I have the car running ok again, but I do not think I ever really set timing, dwell or anything on the carb. I hit 55 this year, and I have "senior moments" with memory.


So where do I begin? What first timing, or dwell? I do believe dwell angle first followed  by timing, then fuel stuff. Is timing set on this with the vacuum advance connected? disconnected? I am using the temp controlled ported vacuum switch in the vacuum circuit for the distributer advance.



The ignition system is standard points, coil and wires. Motorcraft plugs. There is nothing added in the performance arena on this motor, other than the carb. Carb only because I don't have access to an OE one.

Any help at all will be most appreciated. It is possible, the hesitation I feel is normal, as it has been many years and many cars in my life since the 70's cars of my youth.
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#2
Dwell first, then timing. Changing the dwell changes the location, in relation to the crankshaft, when the points open and close, so also changes the timing. Adjust timing with vacuum line removed and plugged. You also need to keep the idle speed under control so the mechanical advance doesn't effect the initial timing, advancing the timing will increase idle speed.

I would start with initial timing in the 10° to 12° range.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#3
The hesitation could be a bad accelerator pump diaphragm, or you need to increase the pump shot and/or it's intensity. I have found on my 351Cs that the 37 discharge nozzle and a more aggressive cam fixed the problem. Here's a good video from Holley.

https://www.youtube.com/watch?v=k-Nx5HEzvlY


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#4
(04-29-2019, 09:13 PM)Don C Wrote: Dwell first, then timing. Changing the dwell changes the location, in relation to the crankshaft, when the points open and close, so also changes the timing. Adjust timing with vacuum line removed and plugged. You also need to keep the idle speed under control so the mechanical advance doesn't effect the initial timing, advancing the timing will increase idle speed.

I would start with initial timing in the 10° to 12° range.

So far I have found the dwell to be at 48, books I have here want 30. I did one feeler guage adjustment to .021 and left the car not running, adjusted again, too much. try again in the morning.
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#5
You need a gap of around 0.016" to get 30 degrees dwell.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#6
(04-30-2019, 05:50 PM)Don C Wrote: You need a gap of around 0.016" to get 30 degrees dwell.

As it stands weather I set the gap at .016 or .021 I am still reading ~40 on the dwell meter. I am thinking a problem with the plate in the distributer. Back when I purchased the dist from a local parts store it was equipped with a "lifetime warranty". Last night I put it to a challenge, new distributer will arrive Saturday night.
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