Anyone have a cure for the dreaded stumble for a 66 352 2 bl till the truck warms up
I've used a 500cfm carb and that seems to work but the gas mileage is horrible Is there something I can do to the original carb to solve this issue

 

Do you have any kind of hot air nozzle that draws air from around the exhaust manifold to the air filter housing?

 

Does it have a manual choke?

 

Does it happen only with a cold outdoor air ambient temperature? If you answered yes then it could be carburetor icing. A hot air intake would help this.

 

Carbs need to be tuned after installation. They have different circuits - idle, cruise, power, that need to be tailored independent of each other to any given engine it's installed on. The bench settings will only be close enough so it will start and idle but that's it. The 500 cfm carb is likely running so pig rich it would probably start without the choke. The downside is all that wasted fuel out the tailpipe and fouled plugs.

Go through the original carb carefully, download the manual first and study it. It's all simple stuff but there are a lot of individual steps and settings, each one has to be optimized and ya can't skip any of it or it won't work right. Shortcuts don't play well with carbs.

The one thing to watch out for with original carburetors that are a "gotcha" for some, after a lot of miles the throttle shaft wallers out the mounting holes in the air horn from excessive wear and allows a vacuum leak. This can't be compensated for by adjusting anything or tuned around, vacuum leaks cause poor engine response at part throttle and low RPM - right where most driving is done. Carb vendors sell bushing kits to fix this.

Other than that most carbs ordinarily will work great if cleaned thoroughly with solvent and shop air, gaskets and parts like the accelerator pump and check valves &c are renewed. Without seeing it we can only guess. Make sure timing and ignition is squared away, this is the most common carb problem believe it or not. Then make sure there are no vacuum leaks anywhere. A mechanic's vacuum gauge is real helpful with engine and carb tuning.

 

Ambient temp certainly affects it. You have to pull the choke or it will stall till the truck warms up. Its done this since new. I have a friend with an identical 66 camper special and his does the same thing. I am in southern ca. and it was 90 degrees to day and I had to use the choke. The truck will start on the first revolution and idle perfect. You either pull the coke or pump the pedal a little or it will die when you take off. Once it warms up its ok. Put a bigger carb and its no problem

 

Most carbed motors won't run very well or have much power until they've warmed up a few minutes ...riding mowers, chain saws, old cars and trucks. Modern fuel injection spoils us by compensating during cold starts. If your carbed motor runs right during cold start it's probably set too rich for normal operation.

 

Good point, is there even really a problem here. If the carb is tuned right it's going to need some choke for a few minutes, if you want to drive it right away in stop and go. Manual choke works best for this. Don't forget.

My slick was getting around 9 mpg hiway driving as careful as possible. So yanked the the circle track 500 CFM 2bl and installed an Autolite and tuned it. Now it gets 17. But it's definitely a little more cold blooded on a cold start. Needs several pedal pumps full choke, sort of routine on a cold morning. No technique was required before with the old fire hose carburetor. I messed around a little tuning it but could never get it where I wanted it.

Incidentally a bigger carb won't really help power too much except at the high end, and usually is restricted by exhaust limitations anyway. Waste of money if it can't be utilized. Nothing much about drag racing translates too well to a daily driver on the street.

If the carb is way too big, it won't have enough air moving through it to give a good signal through the Venturi and will have low RPM performance problems just off idle and transition and part throttle, won't idle smoothly. Running too rich "loads up" the engine idle and fouls plugs. Hotter plugs will not fix this, etc. it will run great at full throttle winding out above 4000, but how often do you drive like that around town?

 

Ditto: On my 65 with the 352/390, found starting could be a pain in the backside especially on a cold winter morning. Once I learned how my pumps of the accelerator pedal and the amount of choke it required to get the engine to start and warm the engine settled in.

Used to monitor gas mileage on the 352/390 and found it ran around 9-12 mpg, decided I did not want to know and stopped monitoring.

Something may want to consider in the future, when I went to electronic ignition the 'cold start' was no longer an issue, not sure if MPG improved.

 

1965/74 F100/350 V8: The original carb is the Auto-Lite/Motorcraft 2100 series 2V:

Bogging down, hesitating, stumbling from a dead stop or when accelerating at speed in indicative of a defective accelerator pump and check valve.

 

Bill
I have wondered about the accelerator pump, but when I move the throttle under the hood it pumps a strong strea of gas from both ports. Its easy enough to put a kit in it and see if it solves the problem just havent wanted to spend the money. I hopr you are right but will make feel pretty stupid if you are right and I was just to cheap

 

Before the fur starts to fly and food stains splatter the wall...

You say a 500CFM 2V? 2300 HOLLEY?

Back when... a carb'd engine required two tune-ups a year, one major and one minor. Both required setting the automatic choke for whatever upcoming season.

If the engine is in good shape (vacuum readings), and the IGN is up to snuff, there is no reason for hard starting and wearing the accelerator pump out. You calibrate the carb to factory settings and go from there.

The gasoline falls out of suspension on a cold carb'd engine. That is why there is a heated cross-over passage under the carb, correct choke settings and fast idle. You should be able to get a cold start by just turning on the IGN, floor the throttle pedal once, remove the foot entirely and crank.

 

Don't take the shop motto to heart. it's there to remind us to not do that. The second one if followed will fix 75% of carburetor problems.

 

I always heard it as "90% of carburetor problems are ignition related."

Don't overlook the accelerator pump overtravel lever/rod. There are 4 holes at one end, two in the other. It allows for tailoring the amount of pump shot depending on temperature.

Second hole from the top is the 40° to to 80° setting for example. Anyway if the timing is squared away and idle mixture set right with good manifold vacuum signal it should run smooth.

 

After looking at this problem for some time and checking everything over I discovered the vacuum hose from dist to carb was loose. Virtually no friction on either end when I took it off. Pulled dist. cap off and pulled line loose from carb Connected hand vacuum pump. When I used the pump the vacuum advance would only pull the advance less than a 1/16 of an inch and go back before I finished with one pump of the vacuum pump. Changed hose made a big difference, but vacuum bled off slowly. Probably need new vacuum advance. Truck has not had a noticeable stumble, will check again in morning when it is stone cold.
Thanks to every one who gave me suggestions.