Backfiring, sputtering form carb

[oldhumphrey]

Hello,

I have just bought an 81 (not EB) bronco, 302. This problem of backfiring and sputtering only happens when the engine gets to operating temp and only on acceleration. It has progressively gotten worse over about ten instances of driving it. Recent reciept shows carb rebuild at a well known shop in Greeley, CO. The engine idles great (just a little miss), starts right up, even when cold, and runs and accelerates strong until it gets to temp (about ten to fifteen minutes of driving). I have pulled the accelerator pump and checked it. Looks fine, new, no cracks or anything. Incidentally, twice this vehicle has not wanted to fire after having been driven for a while. The first time, I stopped at my house to grab something, five minutes, then the bronco would not start. It turned over but did not want to fire. I pulled the coil wire from the dist. arked it to the coil post on the dist. and no spark. Two or three days later I checked for spark again and it had good strong spark and then started right up after hooking the coil wire back up. This has happened twice only. While driving, it is very bad when accelerating, but once I get to speed and cruising, it is fine, smooth, and good even at speeds up to 80mph.

Sound like a good challenge?? Can you help?

Thanks guys.

 

[Justshootme84]

Welcome to Bronco Zone!!! Some basic things I would check are the timing, and the vacuum advance for the distributor. Be sure you have no vacuum leaks, as those can often lead you to think the carb is at fault. Some other checks you can do is to pull the spark plugs and check for fouling, or an lean/rich condition. You can also check the exhaust with a piece of paper/dollar bill to detect a miss or vacuum leak. If the paper sucks in or jumps erratically, you have a miss. Might be a bad spark plug wire, dist. problem or a defective coil. If you have a cracked dist cap, moisture can seep in and cause heck. A good shot of WD-40 helps in a pinch, but a new cap is needed in that case.

assuming all of that checks out and you have a problem with the carb, be sure the choke linkage is not binding. When you have a problem starting, check to see if the choke is not shut. If it is, wedge a stick or piece of wood in the flap to hold it open. Just be careful of a backfire!!! have you checked the fule filter recently? Those get clogged easily and are often overlooked...

Your problem seems to me to be either fuel or ignition related.

 

[Seabronc]

Ditto on Justshootme84's comments and just adding one item, that is the pickup in your distributor. They usually fail when hot and then start working when cold. The backfiring though may indicate a timing problem possibly a worn or streched timing chain. Do the tuneup basics first, like rotor, cap, wires, plugs, timing, etc. Take note of the timing under a timing light to see if it appears to be shifting.

Ignition troubleshooting proceedure.

Good luck,

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