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Old 12-06-2017, 08:35 PM   #1
studeclunker
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cutting out and general misbehav'in

I have a 350 in my '66 Camper Special that isn't running right. I'm not much of a gearhead and am having trouble wrapping my brain around this one.

The truck runs fine up to about forty or forty-five miles an hour. Once it's hot, forty and under. After that it's popping (not backfiring just a popping noise) and kicking(cutting out?) and generally misbehav'in. Also, I have no power going up grades. We have a 6% here that a pickup with a 350 should be able to do fifty or sixty climbing it. This truck struggles at forty.

A friend of mine says this is a carburetion issue (being he's a gearhead and I'm not, I generally listen to him). However I would like to avoid the annoyance of spending the cash for a rebuilt carb only to find out this really wasn't the issue. Yeeeears ago I had seventies vintage Chevys and one of them had trouble with that little cylinder in the valve cover that has a hose attached leading under the carb. I believe it's called a check valve? That was nearly forty years ago though and my memory is rather suspect.

Anyway, any ideas anyone? The problem is getting progressively worse.

Funny thing is, even as bad as it's running, the truck is getting decent mileage.
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Old 12-06-2017, 09:08 PM   #2
65truckowner
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Re: cutting out and general misbehav'in

Sounds like firing problem to me. Check your dist cap for cracks or maybe a plug wire is failing. Pop the hood after dark and start the engine and look for fire jumping around the cap and plug wires
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Old 12-06-2017, 09:39 PM   #3
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Re: cutting out and general misbehav'in

You don't mention what type of distributor you have, but I think 65truckowner is on the right track. It sounds like an ignition problem to me. If you still have a points ignition, I would start by looking at the points and checking gap and dwell. I would also check timing.
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Old 12-07-2017, 08:00 AM   #4
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Re: cutting out and general misbehav'in

Coil could be getting toasty n cutting out.
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Old 12-07-2017, 10:36 AM   #5
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Re: cutting out and general misbehav'in

My list for engines that are generally misbehavin' (easiest first)

1.Vacuum leaks: check all hoses carefully including power brake booster and/or transmission shift modulator if the truck has them.

2. Ignition components: points if installed and as mentioned above timing, cap and rotor, coil, plugs and plug wiring.

3. Mechanical: Fuel pump (should pump one pint of gas into plastic container in less then one minute), clogged fuel lines and/or filters, worn timing chain, worn cam lobes if high mileage older engine, valves.
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Old 12-07-2017, 11:39 AM   #6
GASoline71
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Re: cutting out and general misbehav'in

My first thought is fuel filter. Then check the timing and the condition of your distributor cap, rotor and plug wires.

The "check valve" you're referring to in the valve cover is a PCV valve. Positive Crankcase Ventilation. They can stick and cause a bad vacuum leak.

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Old 12-07-2017, 04:52 PM   #7
Alex V.
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Re: cutting out and general misbehav'in

Is idle also affected when it starts carrying on, or just power at speed?

In the same time frame it's having trouble, will it rev up to, say, 2,500 RPM under no load?

Weak spark will usually cause a problem regardless of load. Lack of fuel will get worse, the longer and heavier the engine is under load.
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Old 12-09-2017, 09:00 AM   #8
Boog
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Re: cutting out and general misbehav'in

1 fuel filter
2 gas cap (vented or non vented)
3 mechanical ignition advance inside distributor seized up <-------
4 internally collapsed muffler or other exhaust restriction
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Old 12-09-2017, 12:19 PM   #9
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Re: cutting out and general misbehav'in

make sure the plugs have the correct reach, sound like the same problem I had. My plugs were too short for the heads.
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