351C miss and poor performance


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Well-known member
Dec 16, 2010
Reaction score
Colorado Springs, CO
My Car
71 Mach1 351C 4V
02 Deluxe Convertible
67 Fairlane GT 390
I have a 71 351C original to the car.  When I rebuilt it a few years ago, the 2v heads were milled along with the block a total of .029 to both raise compression and to true the block face.  I added an Edelbrock 4v manifold and Holley 4v carb and an improved Comp cam at the same time, and am running a Pertronix Ignitor system.

I have 2 historic problems: a) the car is the most cold-blooded animal I've ever driven, and ) I have a noticeable miss, most notably under any kind of acceleration.  It's not always noticeable, but it's there, and it really robs power.  When the miss isn't there, the car runs like a raped ape.  I'm looking for solutions for the miss.  What's the order of things to check?  Best way to check?

Thanks in advance!


Check the coil, maybe do a swap test for another, a bad coil can produce that kind of problem. Does the Petronix getting a clean 12 volt ? Spark plugs wire quality ? Is the timing correct ? advance curve ? The valvetrain when you milled the heads ? Geometri ? Can you monitor fuel pressure ? is the Carb set upp correct, jets etc. How does the sparkplugs look ?

I would start with the coil and ignition system then Fuel then valvetrain :)

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First I would test the Pertronix! 

What do you have there - I, II or III ? 

Does it get full 12 volts? 

"Cold blooded" could be several things:

- timing. To which timing it is set? False timing could lend to hard starting/running issues... 

- Does the carb or better the choke system (I assume an electrical one) get full power? Where have it been connected to which electrical source? 

The above mentioned are the most obvious ones - then we have to go further... 

Hi Dan (I assume),

I'm far from being an engine guy or a mechanic, but what you are describing is a lot like the issues my 71 351C-4V was suffering. Over the last 12 years, I've learned from others, especially the great guys here, and taught myself by trial and a lot of error. I agree with what the others have said above, but for me, there are other pertinent questions; What distributor is on the car? What plugs are you using? what model Holley carb is it and how old? 

On my engine, which has been rebuilt to basically stock, but with some minor changes to get it to run on 91 octane non-ethanol, the comp ratio was dropped to about 9.8:1 at zero deck with 13cc dished pistons and a Melling MTF2 flat tappet hydraulic cam with slightly higher lift than stock. The power has come from tuning and timing. This is no drag car, but could get me tickets in a heartbeat!

if you have a Pertronix 3 that is probably the cause of the stumbling, and possibly cold bloodedness. If you have a 1 or 2 make sure the ground wire that connects the breaker plate to the distributor body is in place, and as noted before, make sure it's getting the required voltage.

Have you checked the timing ring on your harmonic balancer to make sure 0 is top dead center on #1 piston? if you have the original harmonic balancer the rubber elastomer will be dried out and the ring subject to moving on the hub.

Make sure you don't have any vacuum leaks, hoses, open nipples, and around the intake manifold and base of the carburetor. Extra air will lean out the mixture, making it very cold blooded.

Finally, make sure the automatic choke is functioning properly, no binding, choke plate closing completely when engine is off, and fast idle set correctly.

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