Troubleshooting Help - Engine Trouble

[BirdNerd307]

Hello fellow Bronco folks! Last fall I was driving back to the house when my Bronco started to sputter a bit. I put it into neutral and revved it just a bit to see if that would clear the issue, no such luck. I was able to limp it home and I haven’t had it out since. A busy and cold winter put the diagnosis on the back burner. I’ve replaced spark plugs and the ignition coil. It idles very low at start, eventually dies, pressing the gas pedal usually just kills it. This engine isn’t very old, Jasper 302 with about 1000 miles on it. I’ve confirmed spark, confirmed fuel entering the carb. The only thing that has been done in the recent past is a new exhaust (maybe I’m not getting enough back-pressure?) It ran fine for a month or so after the exhaust install. Timing issue? I’m stumped. Video attached.

 

[4xfun]

It sounds like it could be a fuel issue. Does a shot of starter fluid make it run better?

It could be as simple as water in the gas or trash in the line. Try:
Pulling the fuel line and drain some gas into a glass jar to see what it looks like.
Replace the fuel filter. Also check for one in the carb.
Check the fuel pressure. Mechanical and electric fuel pumps are notorious for failing.
Look at the fuel line condition. A cracked hose can let air into the system.

Once you know those items are good, you can move to checking the ignition system.
Go ahead and tell everybody what type of fuel pump you have, what type of carb or fuel injection system you have, and what type of ignition system you are using.

 

[DirtDonk]

I’ve replaced spark plugs and the ignition coil.

Don’t replace any more parts, please. Not until you verify they’re bad.
New parts are often bad out of the box, which means you would be adding more mystery to an existing problem.

This engine isn’t very old, Jasper 302 with about 1000 miles on it.

Hmm, just 1,000 miles eh? Sounds hauntingly familiar…
Does this engine have a flat tappet, or roller cam?
If a flat tappet, are you using a high zinc oil?
I would probably add a compression test to your list of things to do.

I’ve confirmed spark

Is it a good hot, healthy spark?
A weak yellowish spark is not good and indicates an issue with the ignition system.

The only thing that has been done in the recent past is a new exhaust (maybe I’m not getting enough back-pressure?)

No such thing.
Two little exhaust flow (more back pressure) or too much exhaust flow (lack of back pressure) won’t just instantly happen. And I don’t think it will cause your symptoms anyway.
Not unless something failed in the muffler and perhaps a baffle came loose or something like that. In which case too much back pressure would keep it from working.
You said this is carburetor, correct? If it was Efi, then a clogged exhaust system could mess with all sorts of things.
What does the exhaust sound like when it is running? Did the tone change?

Timing issue?

Possibly. You need to check timing. No matter what…

I’m stumped. Video attached.

Don’t see the video. If you’re not a contributor, for 12 bucks a year, you can’t post it directly here.
If it’s online, on another site, perhaps, even YouTube, you can link it here, then we can click on the link to go watch the video.

 

[B RON CO]

Hi, take the air filter off and warm up the engine. After the choke is fully open, shut the engine. Look into the carb and make sure you have two accelerator pump squirts when you open the throttle. Good luck