1966 F250 352 (stock) with a newly rebuilt 4bbl starts easily, then the RPM's at idle steadily increase to what has to be at least 1200 RPM's. I don't have a tach, but it's clearly idling too fast.

After it warms up in the driveway, it begins running rough and then dies.

The idle set screw is backed out all the way and the manual choke is very "touchy". I suspect a vacuum leak.

My problem: I don't know how to go about checking for vacuum leaks. What's normal? How does one begin to determine if vacuum leakage is a problem? It appears that there is some sort of vacuum port on the back of the engine on the drivers side that appears to go to the transmission. Could that be the culprit?

Gregory Glaser

 

What kind of carb do you have on the engine? That will help determine how to properly adjust the idle, choke, and mixture. Some carbs (holley) have a fast idle cam hidden under the electric choke housing.

If you are running an automatic trans then it is possible that your vacuum tube needs to be attached. If you have a manual tranny then cap the open port. Look around the base plate of the carb for uncapped ports as well. Once you can say for certain that there are no unplugged/capped ports then use ether or starting fluid to find leaks along the intake manifold. Be careful doing this, you don't need to ignite your engine compartment after spraying spark plug wires or the distributor. If the engine RPM increase after you spray an area then that is where the leak is.

 

The carb is a Carter AFB 3012S.

When I originally got the truck, the automatic choke on the carb had parts missing and a manual choke was being used.

When the carb was rebuilt, the rebuilder put the automatic choke back together using spare parts from another carburetor.

I initially thought that the automatic choke was the problem until I reconnected the manual choke and the problem remained.

Until my running problems get sorted, I figure to stay with the manual choke.

The transmission is an MX Cruise-O-Matic.

Thank you for the response and ideas.

Gregory

 

Run by Harbor Freight and get a Vac gauge, about $9.00 you'll be able to determine whats going on. If you had the carb done and the guy didnt install and set it ? what the ? Pull the plugs and see what color they are.. vac leak will be whitish plugs. Starved (fuel)-floats setting should be normal colored plugs provided the idle mixture is correct.

diagnoseengine.php
http://www.iwemalpg.com/Vacuum_gauge.htm
http://www.classictruckshop.com/club...ts/vac/uum.htm

 

RedmanBob,

Thanks for responding.

I think the web links you provided are just what I needed!

As a bit of background, I changed the spark plugs a week before I got the truck running. The old ones I took out were black. Other than the fact that the truck had been sitting for 20 years, the condition of the plugs was the main reason that I decided to have the carburetor rebuilt.

In my local area what often happens is if a mechanic can't convince you to buy yourself a new carburetor, for a small surcharge he'll offer to have your old one rebuilt.

Of course few professional mechanics in their right mind will actually do the work themselves. It's easier (and better business) to send your funky old carb out to be sanitized and rebuilt by someone who does it all day and has the proper tools, kits, chemicals, experience and temperment for the job. This frees the mechanic for other more lucrative revenue opportunities.

The shop that did the work for me is a rebuilder. They don't do removals or installs, rebuild is all they do and they'll do it for anybody whose tall enough to put their money up on the counter.

Yeah, I miss out on a certain element of service doing it this way but if you can get your own carburetor off and on, you get a first class job done right, and if you behave yourself, they might let you watch!

I've also found that when they find you speak the language of cash, there are discounts and cool extras in store for you and your little vaporizer.

Next stop, Harbor Freight to pick up a vacuum gauge. I see only three vacuum hoses on the engine. The distributor advance which I can't use because it is ported. The PCV vapor valve in the valve cover on the passenger side, and something that appears to go toward the transmission from down behind the engine block which I'll attach a hose to and use.

It appears that this is all there is. Have I missed anything?

All the best to everyone,

Gregory Glaser

 

Wish I could help but not much of a Carter/Edel fan here. Somewhere on the carb should vac line probably has a rubber cap on it ? Read the how to on the vac carefully before attempting it. It will do you little good to jump past the foundation part and start turning screws. Follow the sequence, floats dialed in etc. Timing Light ? get it, check it.. yada yada BOL.. get that Gallery going,. picts keep us happy LOL

If the thing sat for 20 years I'd replace all the hoses (all) fuel line included.. thats a snafu waiting to happen.

 

Redmanbob,

Thanks for all the valuable information regarding the vacuum gauge. It's going to turn into one of the best diagnostic tools I have.

As to the gallery notion, why not? What's another rusty F250 between friends. Perhaps it will be a good place to document the revival.

All the best

Gregory Glaser

 

Has to be the optimum tool on these older engines. Besides the brain to make sense of it of course That rusty F250 will be here running strong when the 07 Tacoma takes a plung and becomes a Haundai/Daiwu/etc Tell me it aint so !!