I am working on a friend’s 1979 F-150 4x4 that has a 351M. The truck has the Edelbrock intake, cam, and carb (1406 600cfm) headers and dual exhaust. It has new plugs and wires too. He brought me the truck because it had a really bad hesitation when you would go to WOT from a dead stop. It would “pop” a couple of times and then die. If you were cruising about 30 mph and then go to WOT, it would hesitate real bad but then catch its breath and run real good. My first thought was that the time was off or he had a problem in the accelerator pump circuit……….

I timed the truck to about 14 degrees initial and verified that the mechanical and vacuum advance was working. Test drive resulted same problem. I have had about every combination jet and rod in the carb along with trying the accelerator rod in about every position. Still no luck.

He was wanting to upgrade his ignition system so I thought now would be a good time to see if it would help. I installed a MSD 6T box, MSD Mechanical Distributor, and Blaster 2 coil. Again, I set the initial time at 14 deg. BTDC and verified that the total advance was around 34-35 degrees. STILL same problem from a dead stop when you nail it to the floor. The truck has about 17 – 20 inches of vacuum at idle with a steady needle. I have used starting fluid around the intake and carb and there is no vaccum leak either.

Here is where it gets interesting. I “power timed” the truck (holding throttle at about 2500 rpm until advance was fully in and advanced timing until it missed and then backed off to where it ran smooth) and went for another test drive. Hesitation was not as bad from dead roll. If you use the brake and bring the truck up on the converter and then nail it, it will smoke the tires until you let off. I didn’t get any pre-detonation rattles at WOT or at cruise speed and it started fine but the initial timing is at 32 deg. BTDC!!!! That would make the total timing advance about 53 degrees or so!!! HOW can this be????

Thinking that the balancer had slipped in the rubber, I took the #1 plug out and verified that the 0 on the balancer was really at TDC. I did not put the cam in the truck so I am assuming that the person who did got the cam gear lined up correctly. I have also pulled each plug wire while the truck was idling and do not have any dead cylinders.

Has anyone else had this problem??? Any suggestion would be greatly appreciated. Thanks for reading this message.

 

haney2, I have a 77 stock 351M and I have fought the timing on this thing for years, I just time it by sound of the engine. If I try to time it with a light it won't hardly run, I wish someone could tell me what the heck is going on here, I would really like to get this engine to run right just once. I've replaced everything on the ignition side of the engine I can, also checked dampener marks, checked out the mec. and vac advance all are working ok as far as I can tell, if you get that one fixed let me know how you did it!Al

 

Is the exhaust crossover passage going through the intake
manifold been blocked off or clogged with carbon? My problems
were rough idle fouled plugs and hesitation. It would also
pop back up through the carb. Did everything you guys did and
while I pulled the intake off checking for leaks I noticed
the aftermarket gaskets I had bought blocked the heat passage
under the carb. I used the manifold as a pattern and made my
own gaskets with the exhaust ports open and now I can put my
timing back and it runs like a top.

 

FRANKLIN2:
Thanks for the tip! Since I didn't put the intake on, I had planned on taking it off tomorrow evening and re-gasket just for "piece of mind". This thing has driven me crazy!

Is your intake an Edelbrock Performer? When your heat cross-over was blocked, did you have to run the timing really high too?

 

Yes, it's an eldelbrock performer with a holley 600. I moved
the timing all over the place, but when I had the problem it
ran best with very high initial timing and no vacuum advance-
if you could call it running! It was terrible and I messed
with it for months. I have other fords and was swapping
carbs, distributors, plugs wires, etc. When I put the gaskets
on it tamed right down and runs good. I never could figure
out the original sheetmetal thing that Ford uses for a gasket.
For one thing, it's about $30.00 new. Then I couldn't figure
out how the thing sealed metal to metal? I was thinking of
a sandwich of gaskets on both sides, but when I found out it
wouldn't fit with the performer anyway, I made my own gaskets
out of a sheet I got from the local farm store.

 

Thanks Franklin2:

I imagine this truck has Fel-pro gaskets and blue glue sealing it up! Excuse me for being ignorant on these trucks, but from your last post you eluded to a metal "factory" gasket. Seeing that they wouldn't work with the performer, you made them from a "sheet" you got from a farm store. Did you make metal gaskets? Could a person get some new Fel-pro gaskets and just make sure the cross-over is open and if not just cut them out or do you need to use metal? If so, what thickness and material did you use? Anything "special" about installing the homemade jobs?

You are being a great help, and if this works, you are the King of 351M's in my opinion!

 

Don't get your hopes up too high! Mechanical things have a
way of making us all pull our hair out. Just something to
look for. The metal gasket is a big metal pan that incorporates
the gaskets for both sides and a shield for the intake. They
shield the intake in the middle to keep oil from splashing
up on the exhaust "hot spot" and turning to gum. The small
block Fords have a seperate pan riveted to the intake. My solution doesn't address this oil cooking problem but I was so frustrated at the time I didn't care. I had used some gaskets
from Mr. Gasket for 2v heads but they must have been for
ported heads because they were on the ragged edge of sealing
in some areas around the ports. Try Felpro, but it may be the
pan type and the bottom of the performer may interfere with
the pan.

 

[font size="1" color="#FF0000"]LAST EDITED ON 22-Jan-01 AT 01:45 AM (EST)[/font][p]I run an Edelbrock Performer intake with an 625cfm AFB on my '79 351m, I used the metal gasket(new Felpro) and everything works great. In fact it runs better than it did with the old cast iron intake and 2bbl.

Anyway I still think the problem is in the carb. Have you checked the choke, floats, and fuel filter? Does it hesitate when you gently accelerate to WOT? Is their junk in the float bowl?

 

[font size="1" color="#FF0000"]LAST EDITED ON 22-Jan-01 AT 06:02 AM (EST)[/font][p]The carb floats have been checked (twice), the inside of the carb is spotless, Fuel filter(s) have been changed, fuel pump is brand new and choke has been set by the instructions in the Edelbrock book. I took a known good carb (Carter Competition Series AFB) off my Cuda and swapped it over to the Ford. Still Same problem. At that point I ruled out the carb. It DOES NOT hesitate when you gently go to WOT? What does this indicate? Thanks Ben_E and Franklin2 for your suggestions.....

 

I hate to bring it up but the timing chain may have jumped or been incorrectly installed with the cam. When did the problem appear? After cam install? Suddenly out of the blue?

1977 Ford F-100
280,000 miles
Stock on the outside
modified/rebuilt everything

 

This might not be a lot of help, but I just experienced a similar problem with my Motorcraft 2 bbl 351M. The problem was that I was experimenting with jets and chose jets that were too small. It originally came with size 56 (.056"), and I tried size 50 because I live at 5500 ft, and thought that it would bring the A/F ratio back to close to what factory designed at sea level.

Anyway, the truck would hesitate bad when I would go to WOT from about 30 mph or so. If I backed off the throttle from WOT, it would 'catch' itself and regain power. This was a very jerky operation. It would bog again at WOT.

I replaced the original size 56 jets, and it runs strong. So, maybe you might try larger jets (although I have no idea about Edelbrocks).

Also, I know that float level is critical for proper operation of different carbretor circuits.

I don't know if you've eliminated the carb as a problem.

Regarding timing: I could time my 302 (70 Bronco) almost that far advanced, but then you could notice a miss with a dial back timing light at that much advance. I have initial at about 15, and total at about 45 or so at 2500 rpm's, and it runs good. You can play with the vacum advance by adjusting a nut inside the vacum port on the distributor with an allen head wrench.

Jeff

 

SUCCESS!!!!!!!!!!!!!!
FRANKLIN2 gets the prize! I uncorked the intake tonight and found a set of intake gaskets with no heat cross-overs and a butt load of black RTV. I cleaned the mess up, went to Advance Auto, and purchased a valley pan/intake gasket set. Put it on, set the time to 14 degrees.... and smoked the tires out of sight. NO HESITATION.....

Thanks a bunch FRANKLIN2, you saved what hair I had left on my head......

 

I have the same problem on my 79 351m with a 2 barrel holly carb. Maybe this is whats wrong with mine. I have checked everything you have except this gasket. Is it under the carb or under the intake manifold. I have never done this before but I am mechanicaly inclined, how long will it take to do. Is there anything that I need to know before I do this. Thanks.