On behalf of my 85-year old father who drives a 1972 Chevy Truck, 4-wheel drive, 350 engine, automatic transmission, 4-barrel carburetor (quad-jet?). The truck starts right up and he drives down the road and once he slows and comes to stop sign, the truck dies without warning. If he let it set until it cools off, it starts up again. If he does not let it set until it cools down, it will not start. He said that is not a vapor lock situation. He has taken the coil wire from the distributor cap and put it someplace else to test it for “fire” and it “fires” and he done the same process another time and it did not “fire” Any ideas to help him trouble shoot the problem? Thank you,
If he wasn’t getting a spark, it’s something in the ignition system, like the coil, or wiring, or points/condenser. He’ll need to find a shop that knows old cars/trucks to trouble shoot it.
If he’s sure it’s not vapor lock, which it sounds like, then have him check the wires in the distributor for the points.
The points are mounted on an advancement plate in the distributor. This advancement plate pivots depending on the vacuum. Over time this pivoting of the advancement plate flexes the wires to the points to where the wires start to break and make a poor connection.
Tester
It could be an overheating coil. Next time it is acting up, pour some water on the body of the coil, not the tower. If it sizzles, it is overheated. You’ll need to replace it.
1 Like
If pouring cold water on the coil immediately gets the engine to start when it is hot then the coil is failing. It would be worthwhile to get a complete tuneup though. The point gap could be too close, the condenser might be near failing and the truck may be a few miles short of leaving your dad stranded on a hot road with a long walk.
Another thing to check is making sure power is getting to the plus side of the coil. There could be a bad connection to power causing the power to drop off after the connection heats up and more resistance is added.
It sounds like the choke is failing to open. If it has an electric choke thermostat, look for a broken or fried wire.
You can check for a closed choke when the engine stops. Remove the top to the air cleaner and look. If the choke plate is still closed (on the front of the carb), jam a half inch socket extension in there to hold it open. If half inch is too big try a three eighths. You don’t want to use a screwdriver because it will sometimes hold the throttle open when it slips farther down.
All good answers but these trucks had the 4-barrel Quadrajet carbs that suffered from bad floats. If you pop the top of the carb you will probably find that the “float” no longer floats. The resulting flooding condition will keep the engine from restarting until it cools down. I owned one of these trucks years ago and it suffered the same symptoms even after I replaced the Quadrajet with a Thermoquad. The floats are made of a composite material that starts failing over a short period of time. Unfortunately…the same composite floats are still being sold some 40+ years later.
I agree with missileman about the carb float. But the carb top does not just “pop off” . It takes a degree of care and skill to remove it…Replacement floats are pretty much trouble-free Also, the points ignition is suspect when “no spark” is found. I would replace the entire distributor with an HEI unit off a 1975-1980 chevy V8 engine…Get rid of the points and the weak ignition system…
You say he lets it cool down then that would indicate overheating. But I think you meant something else using “cool down” as just waiting for a little while. Does this happen every time he stops or is this when it first starts it and stops the first time? Intermittent problems are tough but my experience has been it is more likely electrical. Coils can be ok then flaky then ok. An ohmmeter should be able to test it. Electric assist on the choke.perhaps. The Quadrajet front barrels are small so it does take much. Those carbs also had a filter onboard that if you bought a brass one it was too short. Dirt could get into the needle and seat causing a flooding of fuel… The paper filter was the right length. The first thing I would check is the choke. Before starting pop the hood and remove air cleaner. Depress gas pedal twice quickly then one slow down and up. Feet off gas pedal ow. Look at the carb, is butterfly closed? It should e and have a small gap. Turn key and it should startm watch the choke. Does it open as engine warms?
I owned one of these trucks and it was great runner. The 350 had 255 HP. Make sure the “window” on the distributor cap is closed as well.
I would suspect the carb too as I would with any older car driving with ethanol lased fuel.
Anyway we can get rid of ethanol adultrated fuel Folks? its a shame,but this stuff is ruining so much older stuff,ditto on the carb problem,these old trucks were tremendously powerful.
Brings to mind a rumour I heard a few years back,that they were going to formulate a fuel that would ruin old engines,looks like they got it done.I just gave away a good lawnmower that was really starting to give me a fit,I cant prove it,but I feel ethanol had a hand in its problems(as an aside.I had a 5hp Briggs Quantum mower[new in 92] that never gave me a minutes problem-pre ethanol, 16 or so years,Finally the blade brake went bad and the wheels wore completly out,it was still running fine when I took it to the recycle center-Kevin
A good first step then might be getting a tank of non-oxy fuel as a test. At our local Mobil station, the high test is non-oxy and labeled for off road or antique vehicles. Thats all I ever will use for my small engines as well and the Briggs brand conditioner year round. Since I switched to this I have had no fuel problems in small engines.
On that truck though might be time to just shot gun with the float, points, condenser, and coil to just get it done. Of course while checking that wire in the distributor. Parts should be pretty cheap yet.
You have to get enough people together who can prove that ethanol laced gas can damage older engines/fuel systems and file a class action law suit against the state.
The Minnesota Street Rod Association did this. In 1992, when Minnesota mandated that E10 gas be the standard motor fuel sold in the state, at first there wasn’t a problem. Then after a couple of years we started noticing problems in older engines/fuel systems. At first nobody could figure out was was going on. Then the MSRA started monitoring the effects that E10 gas had on older engines/fuel systems. When enough evidence was compiled, the MSRA filed a class action law suit against the state.
Their argument was, that you cannot force the public to purchase a motor fuel that does damage to their personal property. And in doing so, the state would have make compensation for said damages. So the MSRA gave the state two choices. Either provide non-ethanol gas for those older engines/fuel systems, or start paying for damages from the forced use of E10 gas.
The MSRA won the case. And this is why non-ethanol gas is available in Minnesota.
http://www.msra.com/Non-Oxygenated%20Fuel%20List/NonOxyJuly2013.pdf
Tester
I have an early 70’s 4x4 Ford truck. The two most common problems I have are vacuum leaks and carb problems. Both problems can appear out of nowhere, the truck runs fine for months, then one day I start it up, and find it is not working like before, for no apparent reason. The symptom you report could be caused by a lean mixture, as it starts and runs ok when cold, but not when warm. Vacuum leaks can cause a lean mixture. In these old trucks, all the rubber hoses are suspect. Here’s where I’d look. I’ve had all of these problems on my truck.
-
Vacuum hoses breaking near the connectors. Remove each hose, inspect, then replace.
-
Vacuum operated devices leaking. Use a hand-held vacuum pump to diagnose.
-
Inspect the choke plate? Is it closed when cold, and opens as the engine warms up?
-
If the truck uses a heat-riser tube from the exhaust manifold to warm the choke, is all that in place? Those tubes can rust and break, esp at/near the exhaust manifold.
-
If the truck has an electric choke, is it getting power? Is the resistance of the heating element w/in spec?
-
Is the accelerator pump doing its thing?
-
Is the fuel level in the carb bowel correct? If not, check the float for leaks and the inlet valve for sticking.
-
Has all the carb linkage been properly lubed? Any signs of something gummed up and sticking?
-
Does the de-choke operation work correctly?
Ethanol attracts moisture and the molecules adhere to ethanol’s. Use fresh fuel and discard old fuel.Ethanol softens the rubber-like fuel lines and they swell up then choke off fuel line completely. Don’t let small engines sit with gas in them for extended periods.
You can look online for places that sell regular gas but they can only sell it to customers by the can and are not allowed to pump it into a vehicle,
Why are you dragging up old threads?
In addition to dragging up an old thread, this is not true
One can buy gas without ethanol as long as it’s been taxed. It’s the gas at airports that’s the problem (along with some having lead).
Well Tester is completely correct in Minnesota. I can go to the Mobil station and fill my car or my gas can with the premium which is non-oxy fuel. No restrictions. I suppose if you are out east they may have gas police to make sure you only put it in a can, but the pumps are for boats, old cars, etc. that are not filled from gas cans. If this is not the case in your area, I suggest having a conversation with your local legislator.