The Stovebolt Site Forums The Parking Lot Big Bolts 66 gmc running problems

to start with the truck is a 66 gmc 2 ton dump truck 4x4. truck has a 351 v6 5 speed tranny. the truck since i put back on road several months back has ran perfect have put 1-2000 miles on it. recently the truck has begun to quit after the engine gets warm it runs good then just quits paddling the gas usually doesnt help. it may run 5-15 miles before acting up but when it does it will start and quit within 50 feet of starting up when it quits let it sit for a minute it will start back up run 50 ft quit again pull the fuel hose off the carb have someone to grind the engine it pumps fuel. trying to go up a slope it doesnt want to run at all. since the troubles began i have rebuilt thecarb with kit, new coil, new mechanical fuel pump also put a new electric fuel pump ,new fuel lines from tank to carb


http://s1244.photobucket.com/user/brianef/media/IMG_0316_zpswwpizlf9.jpg.html?o=0

Trash in the gas tank temp blocking the fuel line. BTW, notice how I used capital letters, commas and periods. That’s just how us old folks roll.🛠

i forgot to mention i took the tank out drained the fuel flushed it out looked the best i could found nothing.

I 2nd the trash in the tank theory.
Or pin hole in the pick-up tube inside the tank.
Tom

Ok how about the frame mounted filter?
Should be on outside rt frame rail under back corner of the cab.
Have seen pick up tubes rot off or get holes in them so when the gas moves around
The level falls below the tube end, or pin hole.
Some have a Sock on the end of the tube? plugged?
Tom

DOES IT START AND RUN AND IDLE IN NEUTRAL FOR A LONG TIME WITH NO LOAD? Does it rev in neutral after that?

Do a series of tests to figure it out, and don't rely on "new this and new that". You never know.

1. Bypass the filter(s)
2. Try running without the gas cap on
3. Check to see if carb squirts gas down throat with motor off.
4. Do a fuel flow test at pump outlet for 10-15 seconds into a bottle. Good pulsing flow filling bottle fairly fast?


Maybe You did something wrong on rebuild carb. My guess is float level/float drop. Filters clogged, heat soak. Also don't know what fuel pump system you have? Mechanical or electric. Carb only wants 4 psi..........NO MORE than that.
Baffle in tank broken, bad gas, needle valve stuck in carb. .

If all that is good we can talk electrics.

yes it will idle for hrs and it will also rev, i have done a fuel flow test. but i will check for gas squirting in carb. i rebuilt the carb after it started quitting thought the carb was messed up not saying i didnt mess it up though. i have the mechanical pump hooked up rite now but when it quits i have hooked the electric up to see if it made a difference which it continues to keep quitting but i will recheck all the suggestions. what is heat soak?

Sometimes an engine bay/motor/manifold/carb gets got. Hotter than it used to get for some reason, and evaporates/boils out the fuel. This is usually a problem after a motor is shut off and "heat soaks" thru the block/manifold and into carb body. That's why the phenolic spacers are used. I don't know if that is your problem unless you have noticed a huge rise in temp gauge. The V6 is known for extremely good cooling.
Heat can also cause some electrical components to fade. BE SURE your points are set properly.

I don't know the history of this. Did it run good under load until recently, then started to die, then you did that work? I'm thinking it was carb or pump and one or both are still the problem. You need to carefully recheck float level and float drop to specs. Be accurate. Make sure float is not hanging up on side of bowl. Double check all the components, I'E. balls, accel pump skirt, needle and seat, orientation of gaskets and if you cleaned it good enough. What carb do you have? WW ? Rochester? Holley? 2bbl?

Try to remember a moment in the process when something changed. That may give you a clue. Keep testing to be sure it's getting adequate fuel. Go with the mechanical fuel pump if you are sure it's OK. Those pumps are hard to find, right? Make sure the flow test is long enough to detect a blockage forming over time. Remember, if a fuel filters are clogged it will cause what you have. Non fuel quality hoses will collapse.

Take off the gas cap in the near future and run up hill, etc., with it off. If tank/cap is not venting, it will pull a vacuum on the whole delivery system and after a short while...........no gas to carb! But it should do that during idle/rev testing? Gas blowing out somewhere or air puff when cap is removed is a tell tale.

Also because it dies under load, check ALL vacuum ports, hoses and hole plugs for leaks. Can't have any leaks.

Keep reporting any findings so we can all keep thinking on it. Just don't keep any secrets

Hy briane and guys, a bad condenser can cause this kind of problem, if it will run okay for a while and then start acting up the problem could be heat related. Ignition coils also do strange things when they get too hot.

well went out today pulled the fuel line off before the pump just a trickle of fuel blew the line towards the tank with compressed air then started syphoning the fuel thru the fuel line was running full power removed the tankremoved the sending unit flushed it out again this time i found 2 1/2 x 1/2 pices of plastic bag i havent drove it since i put together but hoping that was the problem.

They just don’t run well without fuel. Plastic bags?🛠

started syphoning the fuel thru the fuel line was running full power ..what does that mean? The fuel is picked up by the sender pick up tube, then down thru the cab with mental tubing, then rubber...........What are you syphoning with?

Anyway sounds like Martin was right, clogging sock pieces. Some socks are like plastic "bags"? Unless someone used an actual Walmart bag as a gas cap.

Also..... Martin used capital letters at beginning of a sentence. Periods at end. Commas. Easy to read and understand that way. Using IPad language or texting protocol is rough on us retired guys.

Briane,

Another old guy who has a hard time understanding punctuation and capital free text. Anyway, I hope the problem has been solved. If not, I have a big block V6 in a pickup that had similar symptoms that I thought were caused by lack of fuel. It turned out to be badly burned points. They weren't old, but the resistor wire that is supposed to run between the coil and ignition in mid-60's GMC's was not reducing voltage when the truck was running.

JRMunn

It must have been the little piece of rubber drove it over 100 miles ran great. What i meant full power was it was flowing at max gravity feed. Really appreciate the help. I hate that anyone had trouble with the reading but it is the best i can do.

briane, you got this. Post just the way you just did and all will be good for us old men. Thanks.

Good work Brian. We appreciate you and your joining the forum. We could read your post. We were making fun of each other being old and behind the times. You are just the kind of member that makes us happy to help. Let us know if you need any other help, anytime. You more or less figured this thing out yourself. Just needed to get some ideas. We will be asking you questions about autobody work, I'm sure.

My GMC has the 305 V6, the little brother to yours. There is a forum for 60-66 GMC Trucks....6066GMCCLUB.com