dad's 72 is poping and farting - The 1947 - Present Chevrolet & GMC Truck Message Board Network

67cst · 12-04-2004, 01:01 AM

need help here guys, we think its a carb problem but just thought id ask the experts for help, my dad just bought a beater 72 chevy 3/4 4x4, 350/th350..he bought it without hearing it run because it didnt have a carb on it, we plan on tearing it apart anyways but thought it would be nice to take it for a spin and make sure that everything works first. so whats happening is we put an old quadrajet on it just to fire it up and it is timed, and fires up nice and idles great but when you go for a blast it backfires out the carb, if you acelerate slow it isnt as bad but if you punch it a bit it runs like $hit....any suggestions? we figure its the cruddy old carb but maybe someone else has an idea

thanks, Derek

Hooter · 12-04-2004, 01:18 AM

sounds like a classic case of having a couple of lobes worn out on the camshaft which, as you know is extremely common on a smallblock chevy, my 77 used to run the exact same way till i threw a new cam into it, 4 lobes were almost completely rounded off

72 CustomCamper · 12-04-2004, 01:40 AM

My 402 did that. I found out it had a bent push rod and weak valve springs. Try doing a compression test. Couldn't hurt at least...

Chuck

jimfulco · 12-04-2004, 02:36 AM

Old, bad gas will do that sometimes. It will coat the spark plug porcelain with a conductive film that will cause misfiring, especially under load.

67cst · 12-04-2004, 02:46 AM

jim-never thought about the old gas, it has new plugs and wires but ill pass it on- im not sure if he put new gas in it or not yet, also the compression test is a good idea

thanks guys

Brainchild · 12-04-2004, 04:09 AM

Sounds like it could have a dried out accelerator pump in the carb.Q-jets aren't the best carb to leave setting around.

OhioDan · 12-04-2004, 06:56 AM

Sticking intake valve? Weak valve spring?

johnje · 12-04-2004, 02:42 PM

I just went through that. Truck hadn't run in many years, when I got it started, it backfired out the carb quite a bit. I had several stuck valves and bent pushrods. I can't believe the truck even ran! I just had the heads cleaned up and checked at a machine shop, new springs installed. I'm cleaning up the rocker arm assemblies, should be much better when I get it back together. (Oh yeah, and new pushrods.)

John

12-04-2004, 01:01 AM	#1
67cst i love summertime Join Date: Jul 2002 Location: Kelowna BC Posts: 4,302	dad's 72 is poping and farting need help here guys, we think its a carb problem but just thought id ask the experts for help, my dad just bought a beater 72 chevy 3/4 4x4, 350/th350..he bought it without hearing it run because it didnt have a carb on it, we plan on tearing it apart anyways but thought it would be nice to take it for a spin and make sure that everything works first. so whats happening is we put an old quadrajet on it just to fire it up and it is timed, and fires up nice and idles great but when you go for a blast it backfires out the carb, if you acelerate slow it isnt as bad but if you punch it a bit it runs like $hit....any suggestions? we figure its the cruddy old carb but maybe someone else has an idea thanks, Derek __________________ 1967 shortbox stepside Chevy, 365 hp 327, th400. GLOVE BOX LIGHTS FORSALE, click link for info http://67-72chevytrucks.com/vboard/s...d.php?t=273724

12-04-2004, 01:18 AM	#2
Hooter My other Love Join Date: Aug 2001 Location: Castlegar B.C. Canada Posts: 4,085	sounds like a classic case of having a couple of lobes worn out on the camshaft which, as you know is extremely common on a smallblock chevy, my 77 used to run the exact same way till i threw a new cam into it, 4 lobes were almost completely rounded off __________________ Castlegar B.C.The great white North (Canada Eh!) Hooter_5@hotmail.com First generation Monte Carlo club pictures of my life

12-04-2004, 01:40 AM	#3
72 CustomCamper huh ??? Join Date: Nov 2002 Location: Fredericksburg,Va. Posts: 3,368	My 402 did that. I found out it had a bent push rod and weak valve springs. Try doing a compression test. Couldn't hurt at least... Chuck __________________ 90 Blazer Silverado 350w/ 700R4 and 32" Kelly's "I am a bomb technician. If you see me running try to keep up!"

12-04-2004, 02:46 AM	#5
67cst i love summertime Join Date: Jul 2002 Location: Kelowna BC Posts: 4,302	jim-never thought about the old gas, it has new plugs and wires but ill pass it on- im not sure if he put new gas in it or not yet, also the compression test is a good idea thanks guys __________________ 1967 shortbox stepside Chevy, 365 hp 327, th400. GLOVE BOX LIGHTS FORSALE, click link for info http://67-72chevytrucks.com/vboard/s...d.php?t=273724

12-04-2004, 04:09 AM	#6
Brainchild Still drivin' a Rat Rod Join Date: Sep 2004 Location: Monett Missouri Posts: 4,925	Sounds like it could have a dried out accelerator pump in the carb.Q-jets aren't the best carb to leave setting around. __________________ Rusty Member #13872 Instead of saying.....you are a discomfort in the back of my front.....one should be able to say...... you are a pain in the a$# 71 GMC LWB 49 Chevy 85 Chevy G20 Check out my website

12-04-2004, 02:36 AM	#4
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	Old, bad gas will do that sometimes. It will coat the spark plug porcelain with a conductive film that will cause misfiring, especially under load.

12-04-2004, 06:56 AM	#7
OhioDan Registered User Join Date: Apr 2002 Location: New Carlisle, Ohio,USA Posts: 1,404	Sticking intake valve? Weak valve spring? __________________ LIFE AIN'T EASY WHEN YER FAT AND GREASY! GMC= Got More Class! 1970 GMC LWB, Fleetside, 350/4spd, Flowmaster "40's", 2002 GMC 16" Rallies, cowl hood,and added a bunch of options that weren't there when I started.

12-04-2004, 02:42 PM	#8
johnje Registered User Join Date: Oct 2004 Location: Everett, WA Posts: 17	I just went through that. Truck hadn't run in many years, when I got it started, it backfired out the carb quite a bit. I had several stuck valves and bent pushrods. I can't believe the truck even ran! I just had the heads cleaned up and checked at a machine shop, new springs installed. I'm cleaning up the rocker arm assemblies, should be much better when I get it back together. (Oh yeah, and new pushrods.) John __________________ '67 M37B1 '67 Galaxie Convertible '67 GMC Truck

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