First, our patient: my 1980 F-150 Custom, 300 engine, 2wd, C6 transmission. Completely stock, everything from the factory is there and hooked up, to the best of my knowledge.

Here's the problem. When starting up completely cold (first start of the day), the truck starts great - one pump of the gas to set the choke, one turn of the key to fire it up. When I put it in gear it moves off smartly - no issue at all.

The problem comes after 2-3 minutes. At some point before I get more than a mile down the road (suburban driving, <40 mph), pressing down on the gas to accelerate (such as from a stop sign) causes the engine to lose all power and nearly die. It has never actually died completely, but power drops to essentially zero and the truck moves no faster than walking speed. The only way to recover from this is to feather the gas, and nurse it along until it picks up speed. It will exhibit weakness in acceleration for a few minutes after this, but once the truck is warmed up completely the problem goes away, and I've never noticed it except on the first start of the day.

My first thought is the choke...maybe it's not opening quickly enough? I've rebuilt the Carter YFA carburetor in the last couple of thousand miles, and as far as I know everything is within spec. Something's obviously not right...but what?

 

My first thought is maybe the choke is opening too quickly, not too slowly.

 

I had thought slowly, because (based on letting up on the gas to recover) it seems like it's not getting enough air for the quantity of fuel present. Of course, if I knew that for certain I probably wouldn't be here asking for help...

...so let's assume it's opening too quickly. Does rotating the choke housing another notch or two in the 'closed' direction slow it down? Or does that just mean it takes longer for it to begin to open?

 

"Normal" for carbed engines......

 

What is the outside temperature?

Check the choke stove and electric assist for proper operation.

It sounds like it is opening too slowly to me as well.

 

I honestly don't remember which direction does what and would need to look it up somewhere.

 

Have you noticed it behaves differently in different types of weather? A damp day it's worse than a warmer dryer day?

 

Rotate the spring to the closed position a notch or two and see if it gets better. Some carbs have markings that say "richer" or "leaner".

Go richer. If there is no change, maybe it is the warm air intake. Sometimes a cold, high humidity weather condition can actually make the intake charge too cold.

 

WOW !!! A gripe about being cold blooded ! I guess they are younger than I am . Fuel Injected engines have spoiled people ! I am used to warming up an engine ! My 50 , 52 , 53 All require a warm up . As does my 78 . Suck it up princess ! That is how they work .

 

Might be nominal, but it sure isn't normal.

 

I wouldn't consider it normal, either. These engines operated correctly when brand new, customers wouldn't have it any other way.

 

300-6...

To the left of the engine bay is richer (Driver's side in USA), to the right is leaner.

Yes, there is an adjustment issue, or issue with one of the choke assists or defective parts.

It might not run great when cold, but it shouldn't bog down and try to die if it's working correctly.

 

A lot of helpful responses up above, I appreciate the feedback. I'll try to answer some of the questions here:

1. I can't say for 100% certain, but the problem seems to occur more when it is warm out than when it's cold. It was 60 degrees when I drove it today, and the problem wasn't too bad...it was worse on Friday when it was closer to 65-70 degrees out.

2. As far as engine plumbing goes, the hose under the air intake down to the exhaust manifold is in place, although I am not certain that the vacuum-driven flap inside the snorkus works properly. The choke stove is attached, although the line that runs from the top of the carburetor down to the exhaust manifold broke off last year. I haven't worried about it, since by my understanding this just provides filtering to the air that goes to the choke. The electric assist is hooked up, although again, no certainty that it works correctly.

3. And for the comedians...no, this isn't typical, even for a carbureted engine. I know these engines run best when warmed up, but they don't typically try to kill you pulling out into traffic just because they're not fully warm. As ctubutis correctly noted, customers wouldn't have put up with this.

It's late now, but tomorrow I'll go out and start fiddling with the choke. Part of the problem is that I really only get one shot per day to diagnose this; after the initial test, the engine is warm and it won't happen the rest of the day. I'll keep people updated.

 

You might check all the passageways that the air flows through for the choke stove. It may be possible for dirt/debris to get in there and restrict the air flow. Corrosion inside the tubes/passageways may also have restricted air movement.

 

People did put up with it.

Some ran fine, some were never able to be adjusted properly, probably due to whoever was working on it. Most required regular fiddling.

We had a 283 Chev that would not run cold and died repeatedly till warmed up. Several idiots did "tune ups" on it. My dad finally took it to another guy, who prompty found the rusted pull down bi-metal spring in a well in the manifold next to carb--the perfect place for water to gather, given the rainy conditions in Washington. He fixed it, and it ran good for years after.

So I know they can run right. Normal? OK, maybe not. Typical, yes, I'd say that.

Good luck with it.