Sputters, bogs down & backfires when you step on the gas

[FFWalker]

I'm new to this forum, so any help would be greatly appreciated. I own a 1960 T-Bird Convertible with a 352. The car has sat for 10 years, but three months ago I got her started up and running.

So far I've replaced: radiator, surge tank, fuel pump, fuel filter, water pump, intake gasket, heater hoses, cap/rotor/points/condenser/plugs/wires, and all the fluids. No leaks from the engine.

The car runs great at idle and when I rev the engine. However, I took it out on the road and any time I step on the gas, it sputters and bogs down. If I give it more gas, it gets worse and backfires through the carb.

My first attempt at fixing this was replacing the original coil (50 years old) with a Pertronix flamethrower coil. This seemed to immediately solve my problems. I took the car for a two hour test drive (stop and go) with no issues.

Two days later, I started the car and had the exact same issue as before. The car runs smooth at idle, or if you drive the car and give it VERY little gas. However as soon as you give it more than 10%, it bogs down and sputters.

I've speculated that maybe it's the vacuum advance? I did pull the vacuum line from the carb to the distributor to check the vacuum, which there was some. Car runs a helluva a lot worse without that vacuum line, by the way...

Another guess was maybe my coil burnt out again. If that's the case, could it be the voltage regulator?

Any suggestions? I want to get this car on the road, where it belongs!

 

[Freoway]

Hi. My T-Bird is behaving very similarly. Mine's a 312ci V8 in a '57. I've replaced the coil, distributor cap. Plugs and leads aren't very old. Carburetor is a brand new Holley 600. I was driving along and mine started backfiring and farting a bit. Then it went away for a while and now has returned. Even affects idling. It feels like there's no fuel, but there's plenty. I replaced the coil first off, but that didn't make any difference. I hope it's not a dud! I've also spent time hunting for a decent vacuum leak, but there's none. You may want to try that too. PCV valves, brake booster, vacuum operated wipers, etc. Mine isn't backfiring anymore - just bogging down. I can't believe it's the ignition wires as the problem came on suddenly. Your situation is odd as you had it running well for two days after a new coil, then failing again. I checked timing, dwell, etc. first up of course. I guess you've done that. Curious to see if we have a similar issue.

 

[FFWalker]

I finally fixed the problem and in the end, it had nothing to do with the laundry list of parts I replaced. Instead, I replaced the gasoline. Most gas out there has 10% ethanol, which evaporates at a lower temperature than regular gas. It’s also terrible for old cars. Since these cars sit for a while, it’ll rust your metal gas tank and create a bunch of issues (eats away at seals, etc). It’ll also make your car run like what you described. The simple fix: use “Rec Fuel” - recreation fuel, which is non-ethanol gas. You can usually find that at a marina, since boat owners don’t want the same issues either and also because of the environmental risks of ethanol gas in a boat engine. Hope that helps! It solved all of my problems.

 

[Freoway]

Hi. Sorry for the delay in getting back to you. I've had that problem with fuel as well. We don't have the 10% ethanol here, but our petrol generally goes off after 3 to 6 months of sitting in the tank. I can smell (and taste!) that it's off. It goes a bit caramel in colour and doesn't have the foul taste that fresh petrol does. As for my 'bird, I've sorted out my problem too. The new set of contact points had failed. For some reason, the spring metal section had lost its spring and was barely closing the points. The dwell reading read as it should, so that threw me off. When I put an ohmeter across the points when they were closed, I got 10 ohms - it should read zero. So the coil wasn't discharging properly. I put a new set of points in (same brand unfortunately) and the problem disappeared. I can't tell you how many hours I wasted on that problem!

 

[FFWalker]

Glad your problem was solved! I do believe the amount of time wasted, as I’ve spent my fair share.

 

[Yadkin]

Many of the reproduction parts sold today are made in China and generally worthless. A good set of Autolite or Motorcraft points and matching condenser back in the day ran about $5 to $7. Today that same set is made in a Chinese factory and is sold to the US market for several times that.

Luckily there is an alternative. There are several US manufactures of electronic modules to bolt in place of your point. They cost less than two sets of points yet basically last forever. They require a minor change in wiring, need a full 12 volts all the time. It's an easy change, and saves money in the long run and invisible to anyone unless they take the distributor cap off.