Hi,
I have a 440 in a Dodge Travco motorhome.106k miles. It has an Edelbrock aluminum intake and a Holley Spreadbore vac secondary.
Stock Dodge Electronic ignition.
As I was driving along last night, it started bucking and backfiring through the carb a little. Then it would stop.
If I pulled over and put it in neutral and dry revved it , it would break up bad and backfire mildly through the carb.
I thought for sure it was the coil.
Nope.
So far I replaced the ign wires with MSD 8mm
Cap, rotor, coil and spark plugs
Replaced all 3 fuel filters. I have 4 psi at WOT and about 6psi at idle of fuel pressure.
The Holly was rebuilt about 2 years ago and gas is fresh.
I drove it around for about 2 hrs and did not have any drivablity issues like last night. It pulled a couple steep hills fine. But if I dry revv in neutral, still get that backfiring missing and that tells me there is still a problem. It sounds exactly like a bad rev limiter on an ATV.
Oh, I changed the Elec ign Module and cleaned the terminals on the Resistor.
I have no idea what is wrong with it. Do these things have a rev limiter stock ? I'm running NGK UR5 pugs. The auto parts store showed gasketed spark plugs for all 440's but this engine came to me with peanut plugs and the heads are bevels for the UR5 peanut plugs.
I really have no idea what's wrong with it. Our vacation was ruined and I was supposed to go away with it in two weeks but now I am afraid to go anywhere with it.
I'd be grateful for any help at all. I am a diesel guy and really have no clue with old carbed engines. The carb like I said was rebuilt 2 yrs ago but I don't wanna blow 300$ on a new one unless I know that is the problem.
Also put a miti vac on the Distributor advance. It moved and appears to hold vacuum.

Timing chain stretched maybe. At what RPM does the problem start?

Thousands of old cars run with stretched timingchains.

Measure voltage at coil.
Low voltage could mean crappy spark.

Sure they do but the further it stretches the worse they run. It isn't smart to just dismiss something. It was just another one of the things he could check easily.

My first take beyond checking your voltages at the coil and ignition module would be engine grounds. On my old Mopars, I always build a wiring harness just for grounds (to the battery) so the electrics work as they should.

Don't forget your voltage regulator...

It breaks up at very high rpms dry revving but I don't have a tach on it.
It seemed to run ok today other than that. I climbed two steep hills and it was fine but still has that break up if I revv it up high in neutral.
The terminals on the resistor were cruddy. I cleaned them.
I am not sure what voltage I should see at the coil. This whole external resistor thing makes no sense to me. I tried using a regular 12v coil and it would not even start. It currently says on it it's a 12v coil but use external resistor. I thought you needed a 6v coil and that's what the resistor does ?
I have a double ballast resistor. I have no clue how it is wired or it's purpose..

I thought it may be starving for fuel because the fuel tank sits 25 ft away from the motor but when I tested FP under high rpms while it was running like crap and it was 4psi.
The voltage has always been a little high to me. Reads 14.5 when I first start it then eventually calms down to about 13.5-13.7.
I have an Autometer Pro Comp volt gauge.

Does it do it hot or cold?

Had to try alot of part swapping on my 4x4 79 warlock to cure an intermittant break-up backfire condition that was a little more pronounced in wet weather. Actually ended up being the pickup coil in distrib.

Seems worse or more apparent when hot.
I drove it around for 2 hours yesterday and drove up a couple steep hills and it never even sputtered but still has that high revv break up.
Someone else suggested maybe the bucking while driving was inadvertently cured when I changed the wires or cleaned up the contacts on the resistor.
The dry rev break up might be weak valve springs and they are floating. I really have to rev it hard to make it break up.
The first time this happended was our last trip we took and for the first time I was towing a 16 ft equipment trailer with 3 atv's. Didn't seem to have any issues pulling the weight other than the bucking/stalling. That was the first symptom I Ihad but that "seems" to be gone.

This didn't come out very good..

https://youtu.be/vxb1Fp3rEAQ

I'll try and take a better one.

The problem you have isn't a problem. You are over reving the crap out of that motor. It's an RV motor not a race motor. It isn't designed to rev that high.

Could be valve float, sounds like you're buzzing it up pretty good. Does it go through the gears okay if you have it floored? I know it's a motorhome and it made by be dicey but have you sound it out in high gear and held it there?

Normally would never. I just did it whenit started bucking and popping back .so there is probably nothing wrong with it at this point and whatever was causing it to buck on the highway, I might have cured.
I think I'm gonna putthe trailer back on it and load my skid steer and take it for a run down the highwY and pull a hill or too.
If she runs ok , I'll call it fixed.

In fact I rarely take the RV over 55 because of the 4.56 gears.

Im also wondering if it had a slug of bad gas. The generator was running a little weird too.

What is the timing set at? If it has a ton of initial advance it would be a rotor phasing issue w/ respect to dist. cap when the mechanical advance comes in at higher RPM's. Does it have a tach? I'd be surprised if you could rev that engine cleanly to 5k without valve float.

It's for current limiting. If the coil is allowed to pull full current for extended periods of time it will burn up. It's a double because during cranking power is fed through one side of the resistor, which is actually just a bypass so the coil gets full voltage while cranking. When key is in the run position power is fed through the other side of the ballast resistor, reducing voltage and current. Aftermarket ignition systems like MSD have a current limiting circuit built in so you can feed your coil straight +12v.

Hey I thought I would follow up. I think I either had bad plug wires or bad gas or both but I took the Travco from North East Ct down to Gilbert PA towing a small trailer and then from Gilbert we went to the Diesel Nationals at English town and the motor ran perfect the whole time. The only issue I had was t one point the alternator stopped charging while we were driving from Gilbert PA to Englishtown NJ. I started up the on board generator to give us power until we got to Raceway Park and then the alternator started working again and worked the whole way back to Ct so I am thinking I have a bad connection or bad ground somewhere but the engine ran great.

That's what I think you got or some water in the fuel