I have a 40 Ford with a 305 camaro stock engine except a holley 4bbl on an alum hi-rise. about 50k mi on engine. this happened once in 2019 after a long trip across Nebr. acted like vapor lock so I spaced it off. it continued sporadically over the years, again I thought it was vapor lock issue. on a recent trip from Des Moines, IA to Denver, it started early in the morning when it was cool. I could feather the gas & keep it under control. it got worse as the trip progressed with it so bad in Sterling, CO (125mi from home) I was afraid I wasnt going to get home. I had noticed that the volt meter was showing about 14-15 volts when it was running bad but 11-12 when it ran well. turned off the a/c & radio & it ran well the rest of the trip but I kept it at about 60mph. have had friends suggest a bad capacitor on alt. its a 1-wire GM type. others think a bad coil. one suggested starting with plugs & wires, have about 15-20k miles on them. thought it might be bad gas so I kept re-filling it with premium after getting it real low on gas. fuel filter restriction?? hate to just start replacing things hoping it will fix it. any suggestions?????
Fuel filters are easy to replace, if you haven't done so lately, that's the first place to start. Usually a fuel supply issue will make it so it runs Ok until the carb runs low on fuel, then if you let off the gas pedal and wait a bit, it will start running OK again for a short time.
The alt needs to be checked with a meter. Gauges can be off a little. Needs to make 13.4 ish to close to 14 volts. The fuel, listen to Squirrel and start with the simple, the filter. Mine acted like it was starving for fuel moving uphill, ran great down hill and level. Clogged filter. If vapor lock, check fuel line routing. Move away or insulate from heat sources. Then look at a phenolic spacer or add a return line. I’m running a return line on my carb. No vapor lock issues.
It may not apply in your case, but I struck this sort of problem once.. I tracked it to the factory (porous bronze) filter in the carb inlet.. I blew it out, seemed to have good air flow, refitted it to the carb, but it still had the same problem.. I had another inline filter in the system, so I took it out permanently, and all was good..
I'm going to guess fuel pump but from the limited information provided it's a bit of a crap shoot even taking a guess.
How much fuel hose do you have on your inlet line from the fuel tank? Fuel hose does degrade with time and can cause air to be sucked into the fuel.
Did you change anything on the car that might affect Fuel, ignition or the charging system before this issue started? Ideal voltage out of a 12 Volt alternator is 14.2 volts. It might jump a tad higher for a few minutes if you had to crank the engine a bit to start it or if you kick the AC on max right after starting but as long as it settles back down in a few minutes life is good. Once the battery is charged back up the alternator is going to put back in what the systems draw. Meaning that as long as it keeps the battery fully charged anything between 12.5 and 14.2 is good. I'm just not a fan of one wire alternators on cars. They are great on what they were designed for and that is farm equipment with magnito ignition or a Diesel. I was selling them for that at a Ford New Holland dealer long before the street rodders found them. Changing fuel filters is just maintenance and would be the first thing I did. That and ethanal works great to loosen up crud that had been firmly attached to the inside of old gas tanks for decades. At least that is my experience. I got real good at changing fuel filters on the side of the road right after I got my 51 Merc running back in the early 80's. Still when it comes to things like alternators or generators, test rather than arbitrarily replace. I've known too many guys who run out and buy pieces and replace them without testing anything.
fuel pump & filter was changed about 3 yrs ago when we ran a hard metal line from tank to carb. maybe 4-5000 mi since then. no other changes except a new a/c compressor 3 weeks ago.
I would find someone with an ignition scope to see what condition the ignition system is in. That will tell you if your problem is ignition related, and it will tell you quickly.
so I have been messing with this ocasionally since the post. most of the time it runs fine as long as I'm not using a/c. a fellow hot rodder thats a retired electrician thought the alternator wire to the starter was too small. 10ga in the kwik-wire harness. so I replaced with a 4ga as per the kwikwire tech line suggested. it ran worse. another friend suggested I go to auto-zone & have them check the alt. the battery s in the trunk in a plastic marine battery case. while hooking up the meter I notice the neg batt cable looked loose. everything checked fine. took it home, tightened cable. drove 5 miles in 90 degree heat with a/c on, it ran fine. hope my problem is fixed. sometimes its the simple things we dont think of.
Simplest thing is what’s usually missed especially with electrical and fuel. Most of us over think everything. A slight miss and we’re getting ready to pull a cylinder head off.
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