engine will not run smoothly
 

I am in need of expert help. I have a 1953 ford with a flathead v/8, single Holley 94 carb. It starts and idles fine. When I give it throttle it dies. If I pull the choke about 2/3rd of the way it will run and accelerate fine. when I rev it up and I close the choke it wants to backfire and die. I have rebuilt the carb. Timing is spot on. Accelerate pump is working. It has Pertronix ignition with recommended coil and wires.

Re: engine will not run smoothly
 

my flathead does too when cold unless i have the choke set at exactly the right place. and will continue to be sensitive to the choke setting until it's completely warmed up. and even then, if i leave it on too long, it will create additional problems. it's a sensitive as a thirteen year-old ingénue. it's taken me a while to know where to set it, and when it needs to be adjusted.

IOW, i've found the choke to be much, much more sensitive on my '41 flathead than on any of the other manually choked engines i've owned. and i've owned a lot of 'em.

Re: engine will not run smoothly
 

Possible vacuum leak. Check all the hoses for condition - make sure they are good-ends tend to split. Don't forget the hoses under the dash. . Make sure the nuts holding the carb are tight. Check the screws on the carb (don't go crazy tight on these). While you are it it, check the bolts on the intake. They have a torque spec and tightening sequence.,

Re: engine will not run smoothly
 

I highly recommend checking the intake manifold bolts -they can definitely loosen over time. My '40 Ford developed a case of hard starting, rough idling, and poor throttle response and had me completely baffled. I checked manifold vacuum and it was way off. Tightened all the bolts to correct torque spec and what a difference that made! All of those issues diminished completely.

Re: engine will not run smoothly
 

I hate to give advice because the problems can be endless but here goes. What we use to do at work on all engines was trying to determine if the problem was ignition or fuel. You can take a spray can of carb cleaner and spray it into the carburetor while it is running bad and see if it straightens out. If it does the problem is fuel related or a vacuum leak. We also used the adjustable propane cans, so we didn't make a mess of everything. We run it around the intake and carbs bases looking for vacuum leaks. If the engine doesn't straighten out on the propane. we'd even put propane inside of the engine to see if the intake gasket sucked it up from an internal leak, very rare but it did happen once in a while. Then we look at the ignition system using the scope and finally we'd take a compression check. We were a large fleet, so money was no problem. We'd go ahead and give it a complete tune-up and when that didn't fix it the only thing left was to pull the heads. Usually, we'd find the valves had sunk into the heads on the overheads. They would open just enough to run at idle but not above idle. That was on overheads.


I have a Snap-On scope here at home so I can see the ignition pattern. I have heard so many sad stories about Petronix conversions that I just couldn't recommend one. One terrible story after another. I have lots of spare flathead distributors. If it were mine, I'd try it with a stock distributor and coil. It wouldn't take a 1/2 hour to change it out just to see if it's the problem or not.

Re: engine will not run smoothly
 

I was wondering how long it would for someone to get around to mentioning the Pertronix. They seem to be problematic, especially the 6 volt version, as they seem to be particularly sensitive to voltage levels. Old cars, old wiring.

Re: engine will not run smoothly
 

IME, all solid state componentry is demanding WRT voltage than their analog equivalents. it's their nature. and the presence or absence of things like ballast resistors can be particularly troublesome.

Re: engine will not run smoothly