Hello, i have a friend that has a '69 Bronco, 302 c.i. with approx. 5000 miles on the rebuilt motor and, it has been sitting for about 6 years. Before i get into what i have done to fix the problem, let me explain what its doing. The truck will sit there and idle all day. You can take the throttle on the carb. and as fast as you can, open it. It will take every bit of fuel. No hesitation, no backfire, no skip, nothing. If you do this about 4 or 5 times, then it starts too hesitate, backfire, skip everytime. If you let it idle for a little while, you can throttle it all over again, just as above. If we drive it down the road, it skips, cuts out, shuts off, jumps, leave's ya stranded, etc. Pull it back home, starts up and will sit there and idle. Now, this is what i have done. I have cleaned and rebuilt the carb. i have changed points and condensor, adjusted the points with a feeler gauge, i have timed it to 6 degrees BTDC according too Chilton. Now, about the timing, this truck is all orignal and it came with the vacuum\retard thingy. The book tells me to disconnect and plug the vacuum line from the distributor, if i disconnect the retard hose and adjust the timing too specs. it will idle about 15 degrees ATDC. So, i left the retard hose on, plugged the vacuum advance, timed it, and hooked the vacuum advance back. It run the best this way. Is this the way to time this type of distributor? I have adjusted and rejusted and adjusted again the air\fuel mixtures on the carb. and 3 turns out seem too be the smoothest running. The truck runs alot better now then when i started but, i cant seem too be able too get this thing too drive down the road properly. Does this sound like a fuel pump about too give up? Well, thanks for your time too read this and, i really would appreciate any and all HELP. Rob

 

[updated:LAST EDITED ON 26-Jan-02 AT 04:49 PM (EST)]I think it's the distributor.

Distributors wear out too.
It could be turning somewhat off kilter.
Check for out of round turning.
Also,Check for a *Seized vacuum advance unit*.
This is not un-common.

You mentioned Plugging vacuum advance when setting timing.
You're supposed to plug the *Hose* to the vacuum advance >Not the vacuum advance fitting.

Edit :
On Dual fitting vacuum advance mechanism's,
It appears that a vacuum gauge is to be placed between the hose and the vacuum advance fitting.
This vacuum value it to be compared to the Specs value.


That's all I can think of right now.

Dennis

Oh....Please Don't Ask Me Any Tough Questions As:
"I'm Saving Up MY Memory For When I Develop Alzheimer's"




https://www.ford-trucks.com/user_gallery/displaythumbnail.php?&photoid=144&.jpg
https://www.ford-trucks.com/user_gallery/displaythumbnail.php?&photoid=143&.jpg
78 F-150 429CJ C6 ,Silver w/Explorer Pkge
641/2 Mustang,Pre-World's Fair Car #8092
64 Fairlane S/C waiting for a 390-4spd.
68-Mustang.Sunlit Gold 80,000 miles

 

This might be a stupid, but hopefully you already did this...have you changed the fuel filter, that same thing happended to me, but the distributor would be my main concern, I have gone through a few in my 67.

Good Luck

 

I will definetly check for a worn out distributor, i know for sure the vacuum advance unit is not seized. When the truck is idleing i can take the vacuum hose off the carb. ( advance hose ) and suck very lightly and it will idle up. I can take the other hose ( Retard hose ) and do the same thing, and it will idle down. Now, for plugging the vacuum advance, i plugged it at the carb. and left the retard hose still connected at the vacuum advance unit and at main vacuum source ( manifold ) and put a timing light on it and timed it at 6 Degress BTDC. Is this how you time a dual vacuum advance unit? I have never messed with one of these.I put a new fuel filter on and checked it for being plugged also. Its still like new. Does anyone else have any suggestions. Let me ask ya'll something else, would rust on the valves and\or valve seats cause this truck too spit and sputter under a load and not at idle? Thank ya'll very much for the help, i appreciate it. Rob

 

I would also check the fuel pump. It should be flowing about 6 - 8 psi.

 

It definately sounds like the fuel filter. I had a '72 with the exact symptoms you are describing. It would run fine at idle, and would drive for a bit, and then it would start hesitating and cut out. If I let it sit for a while, it would start fine and drive a bit further before doing the same thing. What was happening is that the filter would fill up with fuel while it sat, and would run a bit on that fuel, but when it needed to start pulling new fuel, it was too plugged to do so with enough volume. Depending on your truck, you may have multiple filters. I put a stardard Purolator in-line filter in right after the tank selector valve on my truck because the small filter that screws into the carb seems to get plugged easily. This seems to be a common owner-installed item, so you might want to check for additional filters if you're already changed the one under the hood.

Good luck.

J.B. Hebert

 

Start cheap... do the fuel filter first.

 

I changed the fuel filter, same problem. I bought a new fuel pump, same problem. The only other thing is the timing not right or heads. If you hold the throttle about 1/4 way open, it will start running rough, i had my friend hold it open and i stuck my hand at the tail pipe, there was black smoke, and raw gas on my hand. The jets are the same, there #48 in a 2100 motorcraft carb. This thing is driving me crazy. Thank you to all that has replied. Never give up. Rob

 

Floaters in the carb.......Maybe, those things stick all the time, especially with Holleys, Edelbrocks not as much.

 

Carb. is freshly rebuilt, has new spark plugs, points, condenser and plug wires. Rob

 

Well, this has been a fun one. I guess it comes down to this.

Change the fuel pump, or just start banging on it with a sledge hammer.

 

I was reading a web page one time and the guy had his bronco doeing the same thing. He kept messing with the timeing to get it running better, and he also kept finding more rust in the carburator that came up from somewhere.

 

Well, the gas tank is plastic, and the carb. was soaked in carb. cleaner for a couple hours. I rebuilt the carb. with a new kit. The person before me supposedly rebuilt the carb. but soaked the carb. in cleaner with the accelerator pump and power valve still in it. I replaced the fuel pump, hopeing that was the problem, still running rough. I took the distributor apart, cleaned and lubed all moving parts, filed the points alittle, put it back on, still running rough. The only thing else i can think of is, maybe the valves/seats have a slight layer of surface rust that want let the valves seat all the way causing the truck too run rough at higher RPM's. What do ya'll think? It will idle like a brand new motor but, i cant drive down the road with out alot spitting and a sputter'n. Thanks, too all that have replied, i really appreciate it. Never give up. Rob

 

i realize that you have put new plugs in, but are oil deposits forming on any of the plugs? i had the same problem in my 69 and was getting oil deposits on the back two cylinders which created identical symptoms. oil leaks at the valves or rings can cause oil to collect at the back two cylinders and the subsequent deposits cause the engine to essentially run on only 6 cylinders. the smoke at the tailpipe is another indicator of internal oil leaking. good luck.