Loud popping noise after warm up

[Cellnav]

Are you backfiring through the carb? The flame arrestor would muffle it. She's running rich - that plug's got a ton of soot for one hour of running.

[romantic comedy]

Reading your op. If you are correct, then the only thing that is different is the gas.

[ndutton]

Reading your op. If you are correct, then the only thing that is different is the gas.

Gotta disagree. In addition to the fuel, much of the ignition wiring, the exhaust system and the load are different. Alternator too if I recall.

Time for an outboard tank test?

[Marian Claire]

My line of thinking after Dan.Sev's discovery of the partial use of the choke stopped the popping is that he has a time induced lean condition. He is now running fuel thru his boat tank, line, filter etc that he was not doing in the garage. Plugged tank vent, air leak created when he reconnected?? We do have some conflicting stuff. Sooty plug says rich condition, coughing out the carb/flame arrestor says lean condition. Both could say bad timing. But why the time delay? As usual my posts are more question than answer. Dan S/V Marian Claire

[romantic comedy]

Right Neil.

First hook up an independent fuel tank. A gallon jug would work.

Hook the ignition direct to a battery

Not sure about the exhaust.

I have seen bad gas make the engine act bizarre. Took me years to believe it, then it happened to me with a brand new VW engine I rebuilt.

Could that noise actually be ping?

[ndutton]

Could that noise actually be ping?

Not like I've ever heard. One thing about us old guys is we grew up in an era of high compression engines when octane rating mattered. Too low an octane and pinging under load resulted. "Pinging" sounded like marbles inside the engine and occurred in all cylinders simultaneously, a different sound than what we're hearing in the video.

I think the richness as evidenced by the sooty plug (was it all of them or just that one?) comes from the misfire and unburned fuel saturating the cylinder. Said another way, I think it's the result of the problem rather than the cause.

[romantic comedy]

hazard a guess as to that noise Neil?

I have heard a noise just like that before, but I am racking my brain to remember where and when.

[ndutton]

I mentioned earlier it sounded more like a snap than a pop to me and because of that my initial guess was a failure of the coil secondary system, either the coil itself or maybe secondary wires. I was hoping the run in the dark test would show flashes and we'd be done with it but it was not to be. The test didn't eliminate the possibility for me yet but neither did it confirm it.

My next thought was something in the valve train. I thought a compression check at the onset of symptoms would be an indicator then later on we have the information that choke has an effect. The remote tank test was intended to confirm or eliminate the fuel and/or the fuel delivery system as the problem. Exhaust backpressure is still on the table as well.

Wherever this leads we are sure to learn something.

[tenders]

On my first listen it sounded as though the engine suddenly got loaded and is getting bogged down. Is it possible you have a serious intermittent short somewhere, and the alternator suddenly tries to put out its full amperage? A sudden drop in voltage might also disrupt the ignition. I'd try disconnecting the alternator belt and see how she runs. (The engine will run for hours and hours with just the battery connected.)

[jpian0923]

I noticed you finished a rebuild in November-ish. Have you adjusted your reversing gear yet? Just a stab in the dark.

[tenders]

Here's another thought: are you certain you have the plug wires in the proper order on the distributor 1-2-4-3?

80psi is not infallible compression. I wonder if the wires could be misordered and you have a sticking valve that starts working once the engine warms up. Once that starts firing at the wrong time, the engine slows down and backfires.

May I suggest taking the wires off the plugs one at a time as the engine is misbehaving. Wear gloves unless you like a LOT of artificial stimulation.

I would be surprised if the solution to this required anything close to another teardown to address.

[JOHN COOKSON]

Dav.Sev
Does the engine make the popping noise both in neutral and in gear?
One thing we know for sure is that the prop wasn't attached while it was on the bench.
Maybe putting the engine under load causes the popping to show itself.
This might help narrow the list of possible causes down.

At the moment I think we may be looking at two problems:
Grungy plugs indicating fuel or ignition
Some sort of banging noise. To me the noise sounde like it might be external to the engine. Try disconnecting the new alternator drive belt (post #24) and also disconnet the new exhaust and see if the noise goes away. After these two items were added the noise started. Cause and effect? Who knows?

Have you tried pushing on the accessory drive pulley with a piece of wood while the engine is running?

TRUE GRIT

[Dromo]

Here's my 2 cent.
Mechanical fuel pump rocker arm , binding and putting pressure on the cam
Besides that, engine sounds good
Rick

[lat 64]

4 cents

Here's my 2 cent.
Mechanical fuel pump rocker arm , binding and putting pressure on the cam
Besides that, engine sounds good
Rick

That a was my first thought too, but I don't know the geometry. I have an electric pump. I have heard that kind of noise in an old 50's Ford V-8 when I put the wrong fuel pump on.

(funny one: my stupid computer did a preemptive strike on the word "electric". Instead it wrote lactic. I just don't need a lactic pump on my engine. I hate predictive text!

[Dan.Sev]

Sorry it took a few days to post but I hooked up an independent fuel tank, no change at all. I don’t think that it is the reversing gear, I'm not having any problem putting it into gear and it makes the noise in forward, reverse, and neutral. The plug wiring is correct, I triple checked. All of the plugs were that dirty, and I did have to clean my carb again to get her running smoothly on the bench(I cleaned and rebuilt it about a year ago before my rebuild, worked fine then). I'll try disconnecting my alternator and the exhaust flange, and see if I can isolate the problem. Ill also run the wiring directly to the battery for the ignition and coil. I put some thought into it being the mechanical pump, and using an extra piece of heater hose, it seems like the noise is loudest around the valves/exhaust manifold/carb area. Lol. Doesn't isolate it very much, but the fuel pump seemed pretty quiet. I'm starting to think it’s a problem with the valves, maybe the springs or keepers. I just want to exhaust the other more obvious(and easier to get to) things before I go and open that can of worms. If it does get that far I will pull the mechanical pump first and check out the rocker arm and cam.