The 1947 - Present Chevrolet & GMC Truck Message Board Network

Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > General Truck Forums > Engine & Drivetrain


Thread Tools Display Modes
Old 12-06-2017, 08:35 PM   #1
Registered User
studeclunker's Avatar
Join Date: Mar 2007
Location: Fawn Lodge, Ca.
Posts: 127
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.
studeclunker is offline   Reply With Quote
Old 12-06-2017, 09:08 PM   #2
Senior Member
65truckowner's Avatar
Join Date: Oct 2012
Location: mountain view arkansas
Posts: 875
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
65truckowner is offline   Reply With Quote
Old 12-06-2017, 09:39 PM   #3
Senior Member
truckster's Avatar
Join Date: Jan 2001
Location: Orem, Utah
Posts: 4,225
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.
If I didn't build it or fix it, it's probably not mine.
truckster is offline   Reply With Quote
Old 12-07-2017, 08:00 AM   #4
Senior Member
Join Date: May 2004
Location: Binghamton, NY
Posts: 3,003
Re: cutting out and general misbehav'in

Coil could be getting toasty n cutting out.
b454rat is offline   Reply With Quote
Old 12-07-2017, 10:36 AM   #5
Active Member
68gmsee's Avatar
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,885
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.
68 GMC 250/3 speed Saginaw p/b p/s
69 Chevy 350/350 currently in pieces still lookin for a cab
06 Trailblazer
I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive...
68gmsee is offline   Reply With Quote
Old 12-07-2017, 11:39 AM   #6
"I ain't nobody, dork."
GASoline71's Avatar
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,387
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.

'cuz chicks dig scars...

My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread.

The Rebuild of Creeping Death after the wreck

Originally Posted by LONGHAIR View Post
I would never rebuild a 305.
Originally Posted by prostreetC-10 View Post
I love using vacuum gauges as part of the carb tuning process. I hook the gauge to the inside of my garbage can and leave it there.
Originally Posted by Marv D View Post
GASoline71 is offline   Reply With Quote
Old 12-07-2017, 04:52 PM   #7
Alex V.
Registered User
Alex V.'s Avatar
Join Date: Mar 2013
Location: Campbellsville, KY
Posts: 880
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.
Alex V.
1967 C10 Suburban, 350/NP435, Green/Green, PS, PB, HD cooling, charging, shocks, and springs.

1985 GMC C3500 SRW, Sierra Classic, 454/TH400, white/blue.
Alex V. is offline   Reply With Quote
Old 12-09-2017, 09:00 AM   #8
primer is finer
Boog's Avatar
Join Date: Mar 2001
Location: Searcy, Ark. USA
Posts: 7,689
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
69 Chevy stepside, 358/T350, 4.10 posi, 4.5/4 drop, rallys, poboy driver
09 Yukon SLT 4wd, 06 GMC crewcab Z71 5.3, 4.10
All GM..'nuff said,
Member of Jr Nation 88

I stand for the flag and kneel at the cross
Boog is offline   Reply With Quote
Old 12-09-2017, 12:19 PM   #9
Senior Member
tjc's Avatar
Join Date: Jun 2011
Location: burlington,iowa
Posts: 257
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.
Tom in Iowa
68 L88 C10
68 4x4 C10 soon
tjc is offline   Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT -4. The time now is 01:16 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.
Copyright 1997-2013