The Stovebolt Site Forums The Shop Area Engine Shop Truck cutting out and backfires at higher rpm

My truck runs just fine at lower rpm at low speed but if I give it more gas it starts to hesitate and backfire. It just started the other day before that it ran fine and it seems to be getting worse. I am thinking it's in the carb but I thought I would check on here before I start taking things apart. Thanks

Check the wire from the coil to the side of the distributor. If you can wiggle it and make the engine cut out or stumble, chances are the same thing is happening when the vacuum advance moves the distributor housing. Broken strands of wire under the insulation or at one of the terminal ends can cause an intermittent open circuit. It's like turning the ignition switch on and off quickly.
Jerry

Points and condenser, go there first before tearing into carb. When condensers fail the result is poor power and backfire. Worn or improerly adjusted points can be a cause too.

Sounds like the gas filter or the gas line is restricted.Change the fuel filter and see if you have good flow from the tank.

Pete

All good recommendations.
Always check and verify all the easy checks 1st as most times that's where the problem lies. I wouldn't start tearing things down until all easy checks are done.

I concur with going through your ignition electrical subsystem 1st, then progress to the fuel subsystem.

As an example, on 2 occasions my 49 216 started up and idled fine but had a terrible miss and lack of power on acceleration
and mid/high rpms.
1st time was a very loose coil wire. Once reseated it purred like a sewing machine again. It got replaced afterwards.

2nd time the rocker arm shaft had worked loose and it was only hitting on 4 cyls, retightened and it got me home. Lock-tight and retorque has kept it purring since.

Good luck
Dave

Thanks guys I checked the coil wire which seems fine so I will move on to the points and condenser. Is there a way to test the condenser.
Thanks again

The easiest way to check the condenser is to replace it. Have you checked your dwell. Points being too close can cause what you are describing.

How serendipitous! I just did a tune up on the Blue Funk and am experiencing the same situation! The engine fires up and idles perfectly, but cuts out at high RPMs in 3rd and 4th gear.

I've also noticed that the RPMs don't increase, as they did before, when sitting idling and I rotate the dizzy to the left.

I'm gonna check out what you all suggested!

Thanks!

I decided to just get rid of the points all together and I installed a pertronix electronic ignition. Unfortunately that didn't fix the problem. I am now thinking it is the generator because I noticed the truck turning over slower every time I try to start it so I put my voltmeter on the battery when it was running and when it was off and there was almost no difference so I think I will pull it off and take it in and have it tested and see if it can be rebuilt.

the pertronix might very well be your problem, some people have good luck with them, others not so much. I do know my truck has gotten me home every time for 30 years until I put pertronix in it. then I had to ride the bus.

Even if the Petronix unit is a problem for some people (not for me), it clearly is not the cause of your problem (which was observed before you put on the Pertonix unit).

One "fix" for a Pertronix problem is poorly grounded distributor. You might want to run a ground wire from a distributor-cap-clip screw to the head (to a bolt/screw that holds the coil to the head).

The Pertronix does require a good voltage supply and if your having power issues it will not work good. As Tim mentions run a ground wire to distributor, that helps alot.

May be time to pull the points breaker plate and check the mechanical advance springs and counter weights.
Carl

Dan, mine did the same thing a few weeks back. I first thought it was bad gas, but fuel treatment didn't help. I bought the truck three years ago, and other than plugs, points cap and rotor had not touched the engine, so I started in on replacing parts I figured needed done anyway. Rebuilt the carb, new fuel pump and filter, coil, plugs, wires. The cap and rotor looked good. Still same problem. New vacuum advance and vacuum line, no help. Pulled rocker cover and adjusted valves, some were too loose, some too tight. This helped some. Finally decided to replace cap and rotor. Now she'll run 50 plus with no problem, before 42 was max before she started wheezing. I feel silly for some of this, but for less than $200 at least now I know what I have. I even got brave and checked compression, not knowing how many miles are on the 54 engine she has, but was pleasantly surprised with good numbers. It was a process of elimination, be patient and you'll get er. John

One of my trucks had a similar problem once. Ran ok at low speed and level terrain, but would backfire and stall when the engine was under load or on a hill. Had to tow it home once because it would not pull the grade near the house. Turned out to be rust and sediment in the fuel tank and filter. Just a thought.

I think I've got it fixed! I replaced the regulator which took care of the electrical issues and then I took apart the carb and found that the power piston was stuck I freed it up and now it seems to run good there is still a slight hesitation when I floor it but it runs much better. Thanks for all the help!