I've been searching, and haven't found much related to what's going on with my truck so i thought i would post a new topic. I currently have a 1978 ford with a 351m. It is a woods truck and has performed perfectly for many years in this regard. Just this summer the carb started to crap out on hills, and i decided it was time for a 4 barrel upgrade. The truck had the stock manifold with EGR, and the stock motocraft 2 barrel carb. I purchased an edlebrock performer 400 intake, and Holley 670 cfm Truck avenger carb with electric choke. My friend had recently purchased one, and was having amazing success with it in the woods. So here's the problem. The truck has become excessively cold natured, meaning in order for it to start it wants 100 % full choke. Thats not a big deal, so i give it full choke. The thing is that you can not get on it.. If you jump on the peddle it boggs out and dies. Almost like it's getting no fuel. I've tried adjusting the accelerator pump, timing, and nothing seems to change. Truck idles like it just rolled of the showroom floor, but no go. I keep thinking maybe the intake? Hate to think its the carb. I'm not the best carb mech. around but my father has dealt with em all his life. It's baffling him too. Anyone have any ideas? Anyone dealt with this intake?
I just want to go wheeling...... lol

 

I see two possibilities.

1. Check your timing advance vacuum.
Your new carb should have come with two vacuum ports, one for full time vacuum and the other for ported vacuum. If you switched it around, you could get similar symptoms like you describe.
Try switching it around; you'll need to re-adjust the basic timing to get it to run right at first when you make the switch.

2. You may have a serious vacuum leak with the EGR passages not properly mating or being sealed. You didn't mention if you used the correct intake and/or EGR spacer plate and/or correctly designed carb for the setup - all three need to work together. If you have EGR and use a non-EGR intake or spacer (or vice versa), you can have mismatched intake passages, so that you have a huge vacuum leak.

Try this: With it idling, take a propane torch but do not light it. Turn it on a little bit, just enough to hear it hiss, and then a bit more. Play the gas around the base of the carb, the spacer plate and the intake. Might as well check where the intake mates to the heads, too, to check your installation.
This procedure adds a little bit of fuel (propane) to the air mixture, making the engine respond to a change that shouldn't be happening.
If the engine speed changes, then you have found the leak; normally it will increase some, but it may drop.

Good luck, and post back what you found.

 

hmm.
I did try swaping the vac advance around on the two different ports. I believe it on the right one according to the carb instructions.
As far as the EGR is concerned, that kinda what i was thinkin. The EGR is only a spacer sitting between the original intake, and Carb. Edlebrock spec's this intake for the 351m. I will try the propane torch thing though. I do need to get a timing light too..
Hmm...

 

Maybe from all the jostling around in the backwoods you have dislodged something in the carb.

When you put the ***PEDAL*** to the metal is there any back-firing or is it just bogging down ?


Something in the fuel tank has made it's way to the fuel filter ?

 

Manifold or vacuum leaks can cause that problem. Check the brake booster for vac leaks. Check the timing chain and distributor also. Otherwise carb adjustments...

Threads merged.

 

I like the woods thought, but the truck hasn't even made it that far yet lol. I brake booster is brand new, along with the line running to the new intake. Yes when you put the pedal down hard it will back fire. Going back to basic's tomorrow. Check all the plugs, all the wires, where they run to. Did the vacuum leak test, propane torch, to no avail. Didn't really find any leak at all. One thing we did find yesterday is that the vac advance on the distributor wasn't working. Froze up actually. Fixed that, and it ran better. Also the truck does run quite a bit better with the vac advance on full manifold vac, opposed the to timed port on the carb. I'm beginning to wonder if maybe i got a bum carb, or if the intake was worth it. Like i said its and edlebrock performer 400. The right one for the engine. Doesn't seem to like low RPM thought, might have to try something that can handle being bogged a little bit better like a Torquer manifold. Hmmmm.... any ideas?....

 

Oops, forgot. I was also thinking about trying a factory 4 barrel manifold? Better? I know it's cast iron and heavier, but who care, i'm not racing it lol. Check out the gallery and it will make more sence.

 

Perhaps, you need to check the base timing. try putting it at 12 BTDC and hook the vac advance to the ported vacuum.
Let me know how that does.

 

you might want to try a bit smaller jets on the carb, but it sounds like a timing issue being that it will backfire... maybe the vacuum advance on the distributor isnt working right

 

well, so far i have made zero headway lol. Took the carb off the truck and tried it on another truck, a 74 Blazer w/ a 350, and it worked like show room new. Sold the Carb to my friend about 5 minutes after that. Hopefully tomorrow, i will have some happy new for all those in the Forum, that of my truck is running.....

 

Could be that you have a vacuum leak under the intake manifold. Did you use a valley pan type gasket? I had to on my 460 to keep it from leaking on the bottom side and sucking up oil and air.

 

Well as of yesterday the truck is running, using an old Holley 4 barrel carb, and screwing with the timing. Set it to 8 degrees BTDC, and went from there. According to the Valve cover 8 is the correct setting. Truck and only a little outta wack, but it made all the difference in the world.

 

Must have some clogged passages in the new carb somewhere.

 

Thats what i thought as well, but it's currently on my friends 74
Blazer with a 350 in it, and works perfectly so he says....Oh well, thanks for the help everyone

 

Well, Chevy's don't need much carb. They are wimpy, that's why it runs good on there.