Backfiring

[Mark Pietz]

I don't know if I'm on the right thread, or should be over in basic mechanical!

Now I'm really bent out of shape. I got to get my 1980 w/196 running well enough to get it into the garage so I can begin a real makeover!

History: pulled from a field; had been setting for x years. Who knows. Has the prestolite dist. And 1940 carb. I've gone through that carb about six times now in frustration. It's getting the accel pump squirt. This thing backfires through the carb when goosing it, idles fine, though. After it backfires, the engine slows down and idles rough, then eventually recovers, mostly. I've searched the threads about this and cannot rule out a sticking valve, but now just got done running it at idle with the valvecover off. All pushrods spinning and oil filling up the boats. Didn't notice any broken springs.

I replaced the dist. Cap. Timing is right, dist. Works (does advance when I can get it running faster), vac. Can works. I'm going to put new ignition wires on.

Next move?

 

[Michael Mayben]

Advance the timing as far as possible and see what happens.

And...the accel pump "shot" May be way lean, look at the pump shot down the throat, it should be very healthy and fat.

That is an emissions carb setup, if it still has a limiter cap on the idle mixture screw, remove and toss. Then adjust the mixture screw a bit too "Rich" and see if that doesn't affect the spitback through the carb.

 

[Mark Pietz]

I adjusted the accel pump link to give it a loooong squirt, but it still pops. You say healthy - can I open up that teeeny hole a bit? I'll also try advancing the timing (why would that help?).

I have also deep sixed the egr, so that is not in play, nor is the smog pump (what smog pump? ).

 

[Michael Mayben]

Ignition timing has everything top do with a motor tip-in that has had the emissions system "optimized". Simply twist the distributor and see if the condition is better or unchanged.

Do not modify the shooter in the carb, that won't fix this, it wasn't broke from the factory, there is no need to deviate.

 

[Mark Pietz]

No better.
That's about all I can do with this thing today. I'm going to be driving into town tomorrow, will get new plug wires as whatever is on there doesn't look all that great. Can't hurt at this point.

On an unrelated topic, from the "scream" notebook, just now got off the phone with wifey. She's in denver, driving my son's 2001 chrysler minivan (4 banger). Had the oil changed Saturday, calls me now in a panic. Oil light came on. Well, did you pull over immediately and shut it off? No, couldn't find a place to pull over...several minutes.

Oh no now you've ruined the engine. Oil doesn't quite come up to 1 quart low line.
So much for my son's honeymoon coming up on Saturday.

 

[Mark Pietz]

New wires, problem still the same. Timing at 10btdc, still the same.

Oh dear. Perhaps it is the prestolite module?

 

[Mark Pietz]

Maybe the answer is in front of us the whole time, but I won't get to it for a couple of weeks. Bad fuel? This thing sat, and I know the tank has lots of sediment in it. Varnish and crap also? Would that let it idle, but cough and backfire in transition (sometimes I can get it to run fast). Drag out a small length of hose and feed it fresh fuel from a gas can...

 

[Scoutboy74]

Yeah, if nothing else than to easily rule out a potential culprit. Although if your current fuel source is contaminated, you've already done sucked tiny contaminants into your metering block orifices. Switching fuel source now won't get rid of those.

 

[Mark Pietz]

Hooked up a separate line and fed it clean fuel. Still the same. Popping back through the carb when you goose it, but if it gets past that, runs fast and strong. Ignition coil is wired correctly.

Next up to check. There is a dead original cat on this thing, and the muffler is swollen. When I shut this thing down, after a few seconds - bam! Huge backfire out of the tailpipe.

Could this be caused due to the cat and/or muffler? It does pass exhaust gasses.

I know that cat and muffler have to go. I have a new 2 1/4" tailpipe ready to install, and have lined up the matching new muffler for a 345. Just need to cut out the old crap and put in a new muffler and use a reducing neck until I get this thing in the garage and begin the turbo install.

If this doesn't address the popping, then realistically I'm going to just pull the head, remove and clean all the valves, just to eliminate the sticking valve issue.