Ford 302 timing troubles
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Ford 302 timing troubles
I have an 86 Full size bronco. It has a HO 302 from an 85 mustang and a 2v carb. My problem is that i took it muddin last weekend and some wires came loose for my duraspark ingition. i hooked them back up and on the way home it ran terrible. It would backfire through the exhaust and the carb. I thought it was running lean so i changed out the carb, didnt help, so i changed out the distributor, didnt help, i did the coil and the brain box (blue gromet) didnt help. I have no vaccum leaks. during all this it would start and idle fine. i finally took the vaccum advance off in it runs fine, no backfireing at all and its easy to start. The advance is hooked to the base of the carb in the correct spot with partial vaccum. Im at a loss of what to do next, any help would be greatly appreciated.
Hotshot
Joined: Jul 2002
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From: Bend,OR
i would double check the fire order of your plug wires its easy to get them crossed up. ive done it plenty of times. then pull your dizzy cap and make sure its dry in there and not dirty. you probably fouled a few plugs to when the wires came loose so you might look at replaceing them . remeber cheap autolites or motorcraft plugs are all you need stay clear of the plat plugs.
late
late
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Hey thanks for the info, my brain box is hard wired in, and i made sure all my connections are good. i went head and pulled some plugs and they looked good, i moved my plug wires around and i double checked my fireing order, its all correct, still have the problem. it only runs bad when the advance is hooked up, with it off it will hit 5 grand with no problem, hook it up and it does its backfire routine. Is it possible to have too much vaccum, i was also told that i may have a bad magnetic pickup, both distributors were used so i kinda ruled that out, however anything is possible.
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Broncoman, I'd say replace the vacuum advance cannister. If it runs OK with it disconnected, then you're getting too much advance with it connected. Also double check the carb port. The v.a. port should have no vacuum at idle, and increased vacuum as the throttle is advanced.
Direct manifold vacuum to the advance would also cause your backfiring.
You can leave the vacuum advance disconnected until you fix it. The only reason for having it working is for fuel economy. (A good reason at todays fuel prices.
)
Direct manifold vacuum to the advance would also cause your backfiring.
You can leave the vacuum advance disconnected until you fix it. The only reason for having it working is for fuel economy. (A good reason at todays fuel prices.
)
Mountain Pass
Joined: Sep 2002
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From: covington
When you changed the distributor, did you put a new vacuum advance on it, or use the old one. If you used the old one, then it may be bad. The diaphragms in those can go bad, causing a vacuum leak. I don't think it is a vacuum leak though, because a vacuum leak would cause a terrible idle, but would have little affect on part to wide open throttle. This is going to sound goofy, but are you sure you have the vacuum advance hooked to the correct vacuum source. I would start by checking this. Hook a timing light up and look at the results for the advance hooked up and disconnected. Your advance should never exceed 34-36 degrees. It should never drop below around 6-8 degrees. Get the results, If you can't figure it out, post the timing results and we will take a look. Make sure you look at the timing across the rpm range. Also, make sure the distributor wires are right.
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well, today i re jetted my carb(to smaller jets). the carb that was on there was off my friends stockcar, and i only got 12 to the gallon with it on. anyway, i hooked up the advance just for kicks and it doesnt backfire near as bad or as much as it did before. all my wireing and base timing stayed the same. tomorrow im gonna play with the timing and see what happens. it wont backfire with the anvance hooked up now to about 3 grand, with the smaller jets in it now. any opinions about going to an aftermarket distributor with a mechanical advance, if so any recomendations? i plan on keeping it for a while and eventually building a 393 strokermotor to stuff in it. thanks for the info guys
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Broncoman, just curious as to what jets you changed to? I've re-jetted mine several times, ranging from #54 to #62. I settled on #58's; that's where it seems to run the best. Anything above that size makes the exhaust pipe and plugs very sooty.
You can go to an all mechanical advance distributor, but your mpg will suffer. There's really no difference in an all mechanical dist, versus your stock one with the vacuum advance unplugged. All the vacuum advance does is advance the timing under cruise and no/low load conditions, to give better mileage.
I think you've either got a faulty vacuum advance cannister, or too much vacuum going to it. Double check the vacuum on the carb port at idle. You can do it by simply putting your finger over it and feeling for vacuum. The vacuum should increase as the throttle advances.
Broken or loose advance springs could also cause backfiring, but since you've changed distributors, that's ruled out. Even though the backfiring is reduced, the bottom line is there should be no backfiring at all, under any conditions.
You can go to an all mechanical advance distributor, but your mpg will suffer. There's really no difference in an all mechanical dist, versus your stock one with the vacuum advance unplugged. All the vacuum advance does is advance the timing under cruise and no/low load conditions, to give better mileage.
I think you've either got a faulty vacuum advance cannister, or too much vacuum going to it. Double check the vacuum on the carb port at idle. You can do it by simply putting your finger over it and feeling for vacuum. The vacuum should increase as the throttle advances.
Broken or loose advance springs could also cause backfiring, but since you've changed distributors, that's ruled out. Even though the backfiring is reduced, the bottom line is there should be no backfiring at all, under any conditions.
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Im not sure what size the jets i put in there are, but the ones i took out off the stock car carb were ither a 76 or 78, it was hard to read the numbers, that ones that i put in were noticiablely smaller just eyeing them. my vacuum advance port on the base of the carb seems to be functioning properly, it has no vacuum at idle and increases with rpm. i check my mileage with the smaller jets and its just over 10 to the gallon now, however i didnt fillup at the same station i usually do, that could have some adverse affectson my calculations. when i get everything functioning properly and tuned in what kind of mileage can i expect, its an 85 ho 302 from a stang with a hogged out 2 barrell on it.
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Well, sounds like you're making progress, Broncoman. Ten mpg is not bad for an out of tune engine. I'm getting about 12-13 mpg, and your's should get about that with conservative 
driving....
That sounds like the correct vacuum port the advance is connected to.
One more thing to check is the harmonic balancer. Sometimes they will spin on themselves, because the rubber isolator deteriorates. This will throw the timing mark off.
driving....That sounds like the correct vacuum port the advance is connected to.
One more thing to check is the harmonic balancer. Sometimes they will spin on themselves, because the rubber isolator deteriorates. This will throw the timing mark off.