I have been having a power issue for about a year now. Under load, i loose power, like I have run out of gas. What I have done so far. replaced fuel filter, fuel pump, Rubber hoses. My truck had a edelbrock 4v intake on it, with a 2150 mounted. The 2150 had avacuum leak I believe around the throttle shaft. SO recently I replaced it with a holley 4160 off a 390. I have it tuned and am getting better vacuum than ever. But I am still having power lose. I have checked fuel pressure and it is at a good range. Can't remember exactly but at 5 0r 6 psi.

I have put on 3 different fuel pumps since I have had the truck. I am running out of ideas of things to check or replace.

Oh, yeah, 77 F250 2wd 400/C6 SC.

Other things, new gas tank, bypassed midship tank and valve. I do not use ethanol fuel. No sock on pickup tube.

 

Power loss under load sounds like a vacuum advance problem. As you know, vac advance is load related while mechanical advance is RPM related.

Have you checked the vacuum advance diaphragm for any holes/brittleness? How about the breaker plate on the DSII for smooth operation and the wires for sufficient play?

Your timing is set right - ~ 12*BTDC?

 

Well, that was my next thought. Will look at all this. The wiring on the distributor doesn't look too good. Might just replace it. Thanks for the idea.

 

Along that line of thought, then disconnect and plug vacuum advance line and run it up with a timing light through 3000 RPM or so and observe the mechanical advance.

Advance and retard along the marks should move smoothly and without any jitter or stickiness. Should peg at around 34° say. Distributors get worn, sticky, or erratic and will really hork up an otherwise pretty decent engine. Make sure damper outer ring hasn't slipped, that will screw up trying to set timing with a light. I'd think the trouble would lay with the breaker plate. The vacuum advance is load dependent, it's true, but if it's falling on its face under load then the vacuum advance wouldn't factor? There would be a big vacuum leak though. Hm..

 

2150 is a Motorcraft 2V carb used 1975/79.

 

Have you checked fuel pressure under load? A "T" in front of the carb, about 10' of fuel line and tape the gauge to the outside of the windshield (never run a fuel line into the cab!).

I had a similar problem. Fuel pressure fine at idle but power loss/stumbling at load and speed in warm weather. When I checked while running, fuel pressure was dropping to near zero under heavy throttle. I was getting vapor lock on the suction side of the pump in this running condition.

An electric pump mounted low on the rear frame rail fixed it for me.

 

yeah, it had a 4 barrel to 2 barrel adapter plate on it.

 

I've never heard anything good about those adapters, either direction.

 

After 40 years, in the Duraspark distributor in my 1976 460, the stator assembly, which is normally moved by the vacuum advance link, was found to be "stuck" to the (fixed) base plate assembly due to goop (solidified lube) on its pivot surface, rendering the vacuum advance non-functional. A thorough cleaning and re-lubrication got everything working properly again.

 

D4PZ-12A112-A .. Stator aka magnetic pickup coil (Motorcraft DU-1A) / Obsolete ~ Available NOS & from auto parts stores.

1974/79 all FoMoCo V8's with DuraSpark except 1979 LTD/Grand Marquis 351W with EEC (onboard computer).

 

So, here is what I did. I replaced the distributor and fuel pump, and fixed a leaky accelerator pump. I put the dizzy in the same place as the old one. I can not see the timing marks, no matter what tricks I use. So I will time it with a vacuum gauge one of these days. The fall flat on it's face part is gone, but I have a new problem. It spits and sputters at WOT. Now,

I have no spacer under the carb, just the thick gasket. Do I need one and what do they do, or fix? I know, get it tuned before you start looking for fixes for things that might bet fixed with tuning.

Thanks guys.

oh, one other question. My truck leaks oil from every gasket on it. Looking at throwing a gasket kit in it. Looks like a turkey pan gasket is all that is available. would that be whats under that Edelbrock intake?

 

One way to find out would be to remove it; the other way would be to ask the guy that installed it.

 

My timing marks were there, but faded. I had to take a wire brush to clear up the marks and then used white model paint to be able to read the marks with a timing light.
Also, in reading your original post, was the suction tube replaced with the same size? For instance, my new gas tank came with a 5/16 tube while my stock one was 3/8. This reduction could cause demand issues. Finally, there is no sock on the suction tube? I recommend that one be installed. This will only help you. There is always the possibility that debris can get into the gas tank and make it's way to clog up filters, down the line.

 

Have no clue who installed it and don't want to take it off until I have new gaskets.

 

Tried cleaning and painting and had no luck, of course it could be my bad eyes and my el cheapo timing light too. Original pickup tube in new tank.

The sock will get put on when I take out the side tank and refurbish it. Figure I would just order the little parts all together.