I am new to the forum (and my truck) and looking for some fuel system advice. I have a 66 F100 with a 352 V8 with 2 barrell carb. The truck sat in a barn for 17 years till I found and purchased it about 3 months ago. I have been replacing the brake system for the past month so it has not been out on the road till last weekend. The truck idles smoothly, but only with the choke nearly all the way out. When driving down the road it runs a short while the will choke out and die. So far we have removed, dumped and cleaned the gas tank, replaced the rubber gas lines and blown out the metal lines, replaced the fuel pump and fuel filter, and removed, cleaned and adjusted the carb. Only running on choke sounds like it is starving for gas, but I can't find the problem. Any help?

 

Starving for gas...or getting too much air. The choke has to be compensating for one or the other. I'd hook up a vacuum gauge and see if you have decent vacuum. If not then I'd suspect a vacuum leak.

 

Thanks, I will give it a try

 

Do you have a brake booster? If yes, I would suspect something to do with that as you mentioned that you re-did the brake system.

Does the idle-air screw/screws have any affect on the way it runs? If no, I would look for a plugged circuit.

 

It does have a brake booster, but the vacuum hose that goes from the booster to the carb is brand new. I am going to get my hands on a vacuum gauge this weekend and see what I can find. I hadn't thought of the vacuum leak possibility

 

Shhh. I didn't tell you this, but if you spray ether around the base of your carb and other vacuum connections with the engine running, you can hear the engine rev up if you hit a leak with the ether. Just stay away from the alternator and dizzy.

 

Another option that might be a bit easier, if ether is not available, is to do the same thing with a handheld propane torch that is unlit. The gas will be sucked into the leak, replacing the raw air with a burnable fuel, and help you ID the leak - if that is the problem.

I would suspect the gaskets between the carb and the intake are failing, and if you have a spacer there, look between the spacer's mating surfaces as well. Look for for the possibility that corrosion that has eaten away a spot that is too big for regular gaskets to seal up. Also look for that possiblity under the carb as well.

One other possibility is the PVC hose and valve - although I would suspect the hose more than the valve, unless some PO yahoo tried to clean the PCV valve out by opening up or something similar.


Hope this helps.


John

 

Not an authority, perhaps more knowledgeable member can advise, but If I understand correctly the brake booster is running off the Carb.; not sure that would be advisable, imagine from the carb spacer nipple to the booster, since the booster draws considerable amount of vacuum IMO, it could effect the performance of the Carb.

Another possibility, not sure about the 2bbl, some vac. advance operate of primary vacuum and others off secondary, found this out in connecting the 65's 4bbl to the wrong source?? Interested in other member's opinions?? Anyhow, food for thought.

 

I have mine hooked to the carb and it is just fine. The only time that the booster calls for vacuum is when you hit the brakes - unless the booster is bad.

 

After an eventful weekend, progress has been made. The first big event was first thing before any real diagnostic work could happen this weekend the engine stopped turning over. Blaming it on running the battery down I let it spend the night on the charger. Next day even with a fully charged battery the engine still wouldn't turn over. All the prior day's effort to start it resulted in a burnt out starter. One starter replacement later we are back to diagnostic work. Once the fuel line was removed at the carb it was immedietly clear that we had a fuel problem. What was coming out was a mixture of gas, trash, and water. This was after we had removed and cleaned the gas tank, replaced rubber fuel lines, blew out metal lines and replaced the fuel pump and filter. I have no idea how we still had that much water and trash left in the system. Once again we blew out the fuel lines and replaced the filter. Like magic the engine starts and runs without the choke. It still needs a little fine tuning to smooth it out a little, but overall it is running great for a 50 year old truck. We took a cruise around the neighbor hood with no issues. Thanks to everyone for offering up your ideas. It helped a lot in figuring out what to chase next.