Driveabilty issues....

[Workin' Rig]

I need help...

77 F250 400/2bbl

Ok...i had a small vaccum leak at the base gasket ever since i rebuilt the carb last summer...turns out i didnt have one of the carb studs tight...tightned it down and heres where the trouble begins...

Truck idles fine, acclerates fine, passes fine, but when your going about 35-45 and let off the throttle then get back in it the motor will cut out.

It will do this once then be fine for a few minutes. Choke is open, no smoke or anything...

But heres the kicker...at 55 it seems like im having to really flog it to keep it there. (like 1/2 throttle or so). But like i said when i stomp it it comes right to life.

Its got me over a barrel because it acts like fuel starvation at 55...but acts like its flooding around 35-45....

input???

 

[chris989]

I need help...

77 F250 400/2bbl

Ok...i had a small vaccum leak at the base gasket ever since i rebuilt the carb last summer...turns out i didnt have one of the carb studs tight...tightned it down and heres where the trouble begins...

Truck idles fine, acclerates fine, passes fine, but when your going about 35-45 and let off the throttle then get back in it the motor will cut out.

It will do this once then be fine for a few minutes. Choke is open, no smoke or anything...

But heres the kicker...at 55 it seems like im having to really flog it to keep it there. (like 1/2 throttle or so). But like i said when i stomp it it comes right to life.

Its got me over a barrel because it acts like fuel starvation at 55...but acts like its flooding around 35-45....

input???

If you have it in the budget I highly recommend a stoich meter
http://www.summitracing.com/parts/atm-7175

When I built my last motor I installed one.. It takes all of the guessing out of a carb. I increased my power and mileage at the same time.

Other than that, in an old carb you could have internal fuel or air leaks through any number of bores or maybe the bushing for the throttle/butterfly shaft.

Chris

 

[dustybumpers]

Post above is your problem.

The throttle shaft is worn, and out of round. As you apply throttle, it leans out, more throttle to an unworn spot, it goes back to normal.

 

[Workin' Rig]

Damn...im guessing at that point its time for a new carb?

Pissin in the dark here, but a fuel pump wouldnt cause this would it?

 

[chris989]

Damn...im guessing at that point its time for a new carb?

Pissin in the dark here, but a fuel pump wouldnt cause this would it?

I doubt the pump. Most mechanical pumps work until they begin to leak. The diaphragm will leak and fuel will exit through a small weep hole, or possibly into the engine and contaminate your oil.

If the pump is old they are easy enough to change for the security, but I do not think it is your problem. Most likely the shaft causing a vacuum leak. When you rebuilt it, were the the bushing replaced?

Chris

 

[5.0Flareside]

new carb time... HOLLEY FTW!!!

 

[chris989]

One last thing,

When you rebuilt, make sure the base gasket is correct. Did you add a spacer, are you still running and EGR. There are several post here about the plate and gaskets causing a vacuum leak.

Chris

 

[Beach66Bum]

I had visible gas leaks on the side of the 2150 carb when mine had worn throttle shaft. Also had play in it. Idle was affected too, just enough of a small vacuum leak to have the idle always at 1000rpm's. New carb solved everything,

 

[Workin' Rig]

I did not replace the bushing no.

I may just wait till spring and replace the carb and just call it a day...

I noticed today it seemed to start hard when cold...

Im gonna try to rip into this weekend and figure it out...

As far as emissions its a 400 so its all internal.