400 needs a hug

[Bleever]

so my 79 f250 wasnt pulling hills n trailers like i wanted

I added performer manifold (why do I need heat crosover, if "air gap" gives me a denser charge) but I digress

4160 Holley 600 cfm carefully rebuilt
I've tried several jet and power valve combos

Tried a edelbrock 1406 600 cfm tried 2 different jet and rod combos

performer 2172 cam (towing profile)

new timing set, set to 0 degrees

dropped gas tanks, cleaned out, cleaned pickups, new lines new filters, new tank selector, new mechanical fuel pump, stock, Mr gasket reg and f.p. guage, set to 5psi

new cap rotor plugs wires, timing set 12deg advance. (tried 0-15)

so heres the prob:

wouldn't pass emissions, dumping fuel down the hole....bribed the emmissions people.....

idles OK. runs wide open ok....everything else is cough, sputter, back fire, poop.....

crazy, but it's intermittent....last week after I made some dumb luck adjustment, it ran 100 miles per hour (and was not done yet, the power was enormous) during a late night test....next day, wont run: cough sputter poopoo......

any doggone clues?

BTW comperession is and was 105 psi all the way accross........

 

[LEB Ben]

Both of these carbs have adjustable floats, correct? Did you make appropriate adjustments???

 

[GHoss]

Mine was doing the same thing. 400 bored 60 over, cam, Edelbrock intake and Edelbrock 625cfm carb carefully rebuilt but would not pass emissions. I finally set the timing to about 20 degrees advanced and it passed and ran better. My theory is since these came out with offset timing sets the timing marks are not accurate with a straight up timing set. Correct me if I am wrong, but it passed.

 

[Bleever]

Thanks for posts....

I agonized over the new floats in the holley. Used an electric fuel pump to try to get it just right....(easier with the engine not running) with the 1406, it was easier, just did the 7/16's of an inch according to directions....


I gotta think its something else. Because the truck will run amazing one day. then poop the next.....

I somehow think it's heat related, and Crossover related...I have an EGR manifold, everything plugged......


0 degree performer cam....

 

[Mil1ion]

Thanks for posts....

I agonized over the new floats in the holley. Used an electric fuel pump to try to get it just right...


0 degree performer cam....

How much fuel pressure is entering the carb?

It should be 7-9 psi

 

[BuzzGun79]

are you absolutley sure you installed the timing chain & gears correctly...one tooth off is all it takes for poor performance.did you cross a plug wire by mistake?i would also take a good look at the coil & ignition box & magnetic pickup.check the spark from a plug wire it should be blue,a yellow spark indicates an ignition issue..

 

[primetime]

Have you considered the possibility of an electrical problem? Perhaps it`s a shady wire between the coil and ignition box, or box and distributor, or it`s corrosion in the ignition switch. I`ve purchased ignition boxes that weren`t potted correctly or something and have caused problems. Is there corrosion on the trigger wheel inside the distributor? Maybe an intermitten short in the pickup module. Were you having trouble before, or is this a recent developement since you did all the work?