I just purchased a 1979 F-150 tonight. On the way back from the sellers house (who assured me there were no minor or major problems after he tuned it with new plugs, cap, rotors, wires, and a fuel filter) I realized a few things.

1. It bucks when trying to feather the gas. If it's to the floor it won't buck at all but when trying to meander around town or maintain a speed on the freeway it'll buck and the power to the wheels will end.

Is this fixable by tweaking the carb? I'm clueless when it comes to carbs but it just seems like this should be something that a carb would be doing when it's acting up wrong.

2. There's a huge exhaust leak which sounds like a gunshot every 15mins (it's pretty hilarious). I know I have to replace this with new exhaust tomorrow at Midas or Meineke, that much is a given (and I'm not interested in the high-end magnaflow stuff, etc...).

I had a thought and could the exhaust leak that spills fumes all over the road as well as throwing fireballs into the road be a cause for the lack of ability to feather the gas? Could the lack of backpressure cause the engine to just start bucking?

3. It'll die out of the blue, mainly when power isn't applied. Is this again part of the exhaust leak not causing proper backpressure?

Any and all insight would be GREATLY appreciated. I'm going to fix the exhaust tomorrow and see what that might do for me but I'm kind of betting on the carb or somethingelse being the problem.

Thanks for any and all help folks and I hope I find a home in this community and these forums.

Note: It's a 351 4x4 with 4spd manual in case anyone cares.

 

Welcome to FTE!
How well does the truck idle? Is there any stumbling, black smoke, or do you have to stay on the gas at all?

 

It idles just fine. It takes a stomp on the gas for it to start up but once that's done it idles just fine. I'm really starting to think that it's just the exhaust leak that's causing the engine to run due to poor backpressure. The only real smoke I know of is once I'm on the gas (the girlfriend passed me on the way back home and had a headache in the 3 mins she was stuck behind me haha).

Thanks

 

If the exhaust is majorly rotted, the choke stove line could also be rotted, and allowing exhaust to enter the carb all the time. It would be like running with the EGR on, and would give very similar symptoms. I don't think that an exhaust leak outside the engine would cause it to run like that, I have run 400's and 351M's with no exhaust, and they ran pretty good. It also might be a bad power valve causing it to run majorly rich. Any smoke, or a heavy gas smell in the exhaust is a bad thing.
In order to check the choke stove line, you may have to remove the carb, so you might as well remove it and rebuild it. Once you pull the choke stove pipe out, if it's not a complete coil of tube, with no holes or cracks, then it will have to be replaced. If you just remove it, the choke won't work properly.

 

I've never rebuilt a carb before so this is all news to me. Is there a tech writeup on rebuilding a carb? I imagine I need to get the service manuals in order to do this as chiltons or haynes probably won't have any information relevant to removing a carb, checking choke stove line, and the like right?

Thanks for the help so far, it's been very useful.

edit: Woah I just noticed you live in bremerton. I grew up in silverdale/poulsbo for about 14 years of my life (off and on) until about 4+ years ago. GO COUGARS haha

 

Rebuilding a carb is wicked easy, if you can unbolt the thing, you can rebuild it. Just be prepared, have an old sheet laid out on your workbench to catch any small parts, and just pay close attention. Expect to spend about 2 hours on it at the most, and try to have that time uninterupted, so you can take it apart and put it back together in one shot. The only parts that would "jump out" of the carb would be the ball and rod assembly under the squirter nozzles, so after you take the cover off, take the squirter nozzle assemebly off, put your hand over the area where the nozzles were, and turn the carb over. The ball and rod should drop right out. The kit most likely will include new ones, but the rod in the last kit I got was too long, so I just re-used the old one. When you put it back together, drop the ball down the hole for the squirter nozzle assembly where the screw goes, then the rod, then put the assembly back on.
The instructions with the kit include an exploded view, and that is pretty much all that you will need to do the job.

 

Much obliged for that. I'll print this off as a referance for when I am lost hehe.