What messed up now? I can kinda drive it if I screw with the manual choke lever while driving but thats a PITA (especially since the lever is above the shifter). Runs a bit better/longer if I take the air filter cover off but still dies quickly. '78 F250 4x4 4spd.

New fuel pump, new clear filter between pump & tank, new air filter. Rebuilt Holly 4160 4bbl carb and has a elderbrock performer intake manifold. Ran fine in ~70ºf temps (up to ~3k rpm's), now won't do more then idle. It also won't let me open the choke all the way, it just dies (even after 15-20 minutes of idling at ~50ºf ambient). Fuel doesn't 100% fill filter, only fills to about 80% then drains, then repeats...can't find if that's normal or wrong.

I'm so tired of fricking around with this, not understanding ANY of it, I'm ready to sell it. I _want_ to like it, fix it, and drive it but at the moment it's not being helpful

Oh, measured vacuum on the line going from the carb to the distributor (right place to measure??) and at ~1200rpm the gauge said 14, higher idle and it'd go closer to 20.

 

do you still have the smog equipment hooked up. or possibly an egr valve underneath the carburetor. I had this same problem with a 351m. And it turned out that I was losing vacuum through the EGR valve. So I just took off the egr valve and bolted the carb directly to the intake manifold.

 

It sounds like a vacuum leak to me, you want to measure manifold vacuum with your vacuum gauge, it should pull a steady 17-21" @idle.

If you're sourcing a ported (above throttle blades) vacuum signal for your vacuum advance (which you should be) you measured from the wrong source, you want to measure vacuum from a manifold source (below the throttle blades).

 

No emmission stuff on this engine as far as I can tell. The EGR valve "disappeared" when I took the stock manifold and carb off to put on the Holley carb and elderbrock intake. Too much stuff missing from the stock carb to put it on and use it.

Below the throttle plates? hmm... Would a vac port in the intake manifold work for measuring? Have a line with 3-4 ports on it with the brake booster I could use, don't think there's anything else "below" the throttle plates.

 

That will work as well.

 

The gauge flips between 17" and 19". Flipped a bit less once I picked it up off the carb but still flipped quite fast.

Is it possible the air filter is too small and choking it in some way? It's only about 3" tall and all the other ones I've seen are close to 6" tall.

 

doubt it, i run a 3 or four inch air filter, on my 460 and it idles and runs fine..

 

Get a can of carb cleaner and with the engine idleing check for vacuum leaks by spraying along the intake and carb gaskets, listen for a spike in rpm's.

 

after it dies, are the fuel bowls in the carb full? or have they gone down? if you put a different carb on it, it may not be adjusted right for the engine, although that would be pretty drastic.

ive driven my truck with the brake booster line disconnected and sucking air, never died just ran terrible. and thats a massive vac leak.

just by listening to what your saying an d not seeing it myself, sounds like its lean off idle and cant supply enough fuel at a higher rpm.

also idle at 1200? with 14hg? you should idle around 550 with 17-18hg

so somehow your leaning way out, find out how and it'll run good.
read up on adjusting carbs.

 

Dunno about the fuel bowls, I'll have to check either after 5pm or tomorrow. Rebuilt the carb using a Holley rebuild kit, maybe I fubar'd something doing that, although it was drive able until I broke/fixed the shifter ball and got the brakes working.

No way it'll stay running at 550rpm, it wants to die as it is at 750rpm. It's got that old muscle car lope kind of sound at 750.

The 14" was using the vac port for the vac advance on the distributor, got ~18" using a port with the brake booster at 1200 rpm. Would that mean the idle mixture adjustment screws need to come out more?

 

well thats bizzarre, ive got a 390 with a isky cam in it and idles at 500, it lopes a little. if you have a stock cam and your getting a lope that tells me sumthins up with your carb. or vac leak

when you did your brakes did you do anything to your booster?

 

Started with pads, found calipers to be seized. Got new/reman calipers & found MC to be full of s___. Got new/reman MC+booster and tightened the bolt on the intake manifold side of the booster line. Need to bleed the calipers again, didn't get all the air out but it stops, releases the brakes and I don't have to pull the pedal back out with my foot.

I talked to a friend of my dad's who knows these old engines. Didn't seem to care for Holley's but gave me a few ideas, starting with fixing the rather low fuel level in the bowls. Still need to fix the rear/secondary bowl but I was able to drive it up and down my hillside driveway with few problems. The biggest problem was when it stalled 3/4 up the steepest part of the driveway...3 pedals, 2 feet, no parking brake and I really didn't want to back it down with no power steering assist Thank goodness it was in 4wd, thought it was in 2wd...

Anywho... got it to idle down to 600 or so for about a minute, then it just died. Started right up, but I had to close the choke. Evil thing, but it's better now then it was. Certainly likes 700-800 idle better then 600.


Shouldn't the filter between the tank and the pump be full of fuel all the time? Still don't have an opinion from anyone on that...

 

well that sounds better. sounds like a little carb adjustment will get you where you need to be.

edelbrock vs holley is like ford vs chevy, imo stick with the holley.

fuel filter thing: i dont know, all the filters on my truck are solid(not clear)
so idk. on my model t the clear filter doesnt fill up, but thats gravity feed.

 

i believe from what i saw on the clear filter on my truck there is
always fuel in the filter. not all the way to the top of the filter.
more like 3/4 to 7/8ths of fuel and a little air bubble. my filter inlet
and outlet are horizontal. so the air bubble is at the top of the round
filter.

my first thouhgt is fix the floats to proper settings. if no fuel in the
filter. you need to see whats going on with the pump. it sould always
supply a good ammount of fuel to the carb. the truck should not drain
the bowls like you stated at all. seems to be some what a fuel supply
problem.

Once you fix that i bet you will be running rich. you should be careful
of changing the settings on the carb untill you fix the supply problem
from the fuel pump. make sure you have gas in the tank above the
sending unit pickup.

 

I can't get into the tank to check anything. Don't have anything to turn the plastic nut on the mid-ship plastic tank.
Took the carb off and the fuel bowls were full of some gray crap that smelled/looked like paint and/or varnish. WTF? Wasn't there when I rebuilt it and it's kinda the color the inside of the bowls were when I finished cleaning it.
I'll see if a neighbor has something I can use to get the sending unit thingy out, if not removing the rock shield and dropping the tank is the only other option I can think of. Really don't want to run a 5gal tank bungie'd to the bed, but maybe that's a trouble shooting step?

It seems to be the filter that drains & refills, not the fuel bowls in the carb (if they do the same I can't watch it happen). Either way it certainly doesn't get to near full, and doesn't even keep more then an ounce or two in it most of the time.