Can't get it to run right - The 1947 - Present Chevrolet & GMC Truck Message Board Network

the-wreck · 11-07-2002, 08:00 AM

Hello guys and Gals

Out of desperation Im bringing my running problem to this excellent board. I put my truck together recently and can't get it too run well. Its a 350 that ran well before I removed it. Basically all I did was change the cam and carb and clean it up.

Its a 350 with a performer rpm, 600 holley vac. secondary, stock hei dist and mild cam.

It has no power. Part throttle it runs well and it idels well too. When you give it heavy throttle it breaks up and sounds like it drop 4 cylinders. I have worked on tons of smallblocks and have never experienced this. Even had a shop look at it and they recommended a carb (which I tried with no luck).
So far I tried different coil, carb, plugs, valve adjustment, timing adjustments and even tore the timing cover off to check the cam/crank marks (there good).
Im thinking of looking at the HEI dist. next. It has an old module in it as well as pick up coil. I put a new adj. vacumme advance in it but adjusting it has no effectr on the problem.
Any ideas?

JimKshortstep4x4 · 11-07-2002, 09:01 AM

Based on your description of your problems, two thoughts come to mind, the first is your carb and you might check the flow by looking into the primary side of your carb when you accelerate,(you will want to wear safety glasses, just in case), the second thought is did something happen to your cam when you broke it in?

HEI's normally work or don't work and what you describe sounds more like carb. Spark plugs can cause the problem but I understand that you have addressed this.

Good luck!

JIm

the-wreck · 11-07-2002, 09:16 AM

Thanks for you advice. I appreciate anything especially since Im at a loss here and very frustrated.

I actually broke the cam in on another engine. Took it out and put it in this one. It looked in great shape whem I put it in this engine. However, I have thought about a cam problem.

I had a second good working carb on this engine with the same running results.

Woody · 11-07-2002, 09:32 AM

Well these things just drive you crazy. From the description it idles well, and up to roughly half throttle runs well. Then above that it starts missing, backfiring, ect.

I went back and reread your post. The first thing I would change is that old COIL!!! they get hot and start breaking down.

So we need to start with basics. it needs 3 things to run, gas, fire In time), and compression. you have them until higher RPM. My suggestion would be to look at the dist., plug wires & plugs.
start with the dist. As it spins faster the wieght advance the timing. this could be causing problems. Also the coil & condenser are parts that don't like to sit around waiting for you to run them. They get old and start breaking down and when stressed, short out to ground. This could be your problem. Try to find someone who has a chevy and will let you swap dist.

Double Check the firing order!! mixing up plug wires is so easy.

Another idea is the valve adjustments. With the new cam you messed with the valve train so it deserves another look. Could be that the rocker were cranked down so much that as you speed up the engine and oil pressure rises, the lifters start holding the valves open, not until the higher RPMs though.

Good Luck

Huck · 11-07-2002, 09:34 AM

Pull your HEI and bring it to any auto parts pleace as most will test it for free--- at idle, at acceleration, at high speed, etc. Had one where the condenser would crap out--drove me nuts. Also had one where the weights would hit up against the bottom of the rotor and bid off---also drove me nuts. What size wire are you running to the HEI--should be heavier then stock to handle the HEI.
You may want to run the HEI vacuum advance off of the timed vaccum port on the car verses the full manifold vaccum port or vice verse. If the engine has good compression, you've switched carbs, my guess is it's not internal and my $$ bet would be on one of the above. What does a vaccum gauge say at idle?
Good luck

crazy longhorn · 11-07-2002, 09:40 AM

Take a look at the pick up coil, sometimes an internally broken wire will cause a problem.....( it might try to make contact till the vac advance rotates it). to test, unplug the pickup coil, & use an ohm meter. try "worming" the wires around to find a break in continuity.....good luck

the-wreck · 11-07-2002, 09:48 AM

Thanks guys for all your advice. You all are giving me some hope back.
I will pull the distributor and look at it closely. The wire to the HEI is pretty heavy. I put in a M&H wiring harness that was made for HEI. The coil in it is new and we tried a different one witht the same results.

bigjimzlll · 11-07-2002, 10:14 AM

do you have the ignition wire coming from a 12-13v power source? not the ballast resistor? check the voltage at the coil..with the timing light hooked up, and you rev the engine, does the mechanical advance work(with the vacuum unhooked and plugged)I would be willing to bet its one of those..also check the #5-7 wire location...i know I know..just double check it one more time
Jim

71GMC_3/4T · 11-07-2002, 10:42 AM

Check the condenser inside the HEI unit. It should be down toward the bottom plate. I worked on a mid-70s pickup that would run great until you stomped it. When the vacuum dropped, the distributor rotated, and there was a broken wire on the condenser. It was about to drive me nuts until I finally pulled on the wire to the coil. The insulation stretched about 1/4", indicating the wire inside was no longer complete. It had flexed enough times to cause it to break, but would make contact until the vac advance moved it. This would be a cheap fix if that's all it is.

Yellow Cheyenne · 11-07-2002, 12:08 PM

I watched a dyno session on a BB pontiac that sounds exactly as yours is doing. The engine hac been assembled by someone else a brought in to be dyno'd. Sounded very good at idle and would rev up good with no load. Once they would start the pull (actually load the motor), it would back fire and generally sound like crap. The problem ended up being that the cam timing was wrong. When they installed the chain, the gears were lined up on some other marks that were on the gears, not on the correct dots. Might want to check again because the symptoms sound very similar. At first glance, it looked correct on the Pontiac, closer observation revealed the problem.

**John Fabris** · 11-07-2002, 03:10 PM

From reading all of this, no one has mentioned PLUG WIRES.

If the engine idles fine, and in Park or Neutral you are able to rev the engine with no problems, but then when you put a load on it, meaning you put it into drive and the give it gas and it starts to run like crap, then it is most likey bad plug wires.

bigjimzlll · 11-07-2002, 04:33 PM

if you had a 3 key timing gear..and used the wrong mark..diamond or square instead of circle..then the cam would either be retarded or advanced 4 degrees...this would not cause t he problems your having..all it does is lower or raise the rpm range..Im still betting on the mechanical advance or plug wires
jim

the-wreck · 11-07-2002, 05:07 PM

Big- Do you think a mechanical advance malfunction could give me a problem like this?

The MSD plug wires were right out of the box....so chances of them being bad are pretty slim I think.

crazy longhorn · 11-07-2002, 06:52 PM

im not Big, Im Crazy.....but yes if the mechanical advance is stuck it will cause problems like you have & that is a common prob on the HEI's

bigjimzlll · 11-07-2002, 07:39 PM

yea..what crazy said..happens all to frequently....its easy to diagnois though...just unhook the vacuum advance and plug the line...put a timing light on it and rev it up...how much does it advance..any?? that will eliminate or find the problem

jim

lugnuts · 11-09-2002, 08:15 PM

It sounds like something that happend to me when I changed the intake on my 327. I put a perfromer on it and and it ran the same way idle & part throttle it ran fine but when i would get in it , it would spit and sputter & it turned out to be the intake gasket, I changed them and it fixed my prob.

11-07-2002, 08:00 AM	#1
the-wreck Registered User Join Date: Sep 2001 Location: LI New York Posts: 159	Can't get it to run right Hello guys and Gals Out of desperation Im bringing my running problem to this excellent board. I put my truck together recently and can't get it too run well. Its a 350 that ran well before I removed it. Basically all I did was change the cam and carb and clean it up. Its a 350 with a performer rpm, 600 holley vac. secondary, stock hei dist and mild cam. It has no power. Part throttle it runs well and it idels well too. When you give it heavy throttle it breaks up and sounds like it drop 4 cylinders. I have worked on tons of smallblocks and have never experienced this. Even had a shop look at it and they recommended a carb (which I tried with no luck). So far I tried different coil, carb, plugs, valve adjustment, timing adjustments and even tore the timing cover off to check the cam/crank marks (there good). Im thinking of looking at the HEI dist. next. It has an old module in it as well as pick up coil. I put a new adj. vacumme advance in it but adjusting it has no effectr on the problem. Any ideas?

11-07-2002, 09:32 AM	#4
Woody Registered User Join Date: Feb 2000 Location: Georgetown, KY, USA Posts: 631	Well these things just drive you crazy. From the description it idles well, and up to roughly half throttle runs well. Then above that it starts missing, backfiring, ect. I went back and reread your post. The first thing I would change is that old COIL!!! they get hot and start breaking down. So we need to start with basics. it needs 3 things to run, gas, fire In time), and compression. you have them until higher RPM. My suggestion would be to look at the dist., plug wires & plugs. start with the dist. As it spins faster the wieght advance the timing. this could be causing problems. Also the coil & condenser are parts that don't like to sit around waiting for you to run them. They get old and start breaking down and when stressed, short out to ground. This could be your problem. Try to find someone who has a chevy and will let you swap dist. Double Check the firing order!! mixing up plug wires is so easy. Another idea is the valve adjustments. With the new cam you messed with the valve train so it deserves another look. Could be that the rocker were cranked down so much that as you speed up the engine and oil pressure rises, the lifters start holding the valves open, not until the higher RPMs though. Good Luck Last edited by Woody; 11-07-2002 at 09:34 AM.

11-07-2002, 09:40 AM	#6
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,403	Take a look at the pick up coil, sometimes an internally broken wire will cause a problem.....( it might try to make contact till the vac advance rotates it). to test, unplug the pickup coil, & use an ohm meter. try "worming" the wires around to find a break in continuity.....good luck __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

11-07-2002, 10:14 AM	#8
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	do you have the ignition wire coming from a 12-13v power source? not the ballast resistor? check the voltage at the coil..with the timing light hooked up, and you rev the engine, does the mechanical advance work(with the vacuum unhooked and plugged)I would be willing to bet its one of those..also check the #5-7 wire location...i know I know..just double check it one more time Jim __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA

11-07-2002, 10:42 AM	#9
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	Check the condenser inside the HEI unit. It should be down toward the bottom plate. I worked on a mid-70s pickup that would run great until you stomped it. When the vacuum dropped, the distributor rotated, and there was a broken wire on the condenser. It was about to drive me nuts until I finally pulled on the wire to the coil. The insulation stretched about 1/4", indicating the wire inside was no longer complete. It had flexed enough times to cause it to break, but would make contact until the vac advance moved it. This would be a cheap fix if that's all it is. __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

11-07-2002, 09:01 AM	#2
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Based on your description of your problems, two thoughts come to mind, the first is your carb and you might check the flow by looking into the primary side of your carb when you accelerate,(you will want to wear safety glasses, just in case), the second thought is did something happen to your cam when you broke it in? HEI's normally work or don't work and what you describe sounds more like carb. Spark plugs can cause the problem but I understand that you have addressed this. Good luck! JIm

11-07-2002, 09:16 AM	#3
the-wreck Registered User Join Date: Sep 2001 Location: LI New York Posts: 159	Thanks for you advice. I appreciate anything especially since Im at a loss here and very frustrated. I actually broke the cam in on another engine. Took it out and put it in this one. It looked in great shape whem I put it in this engine. However, I have thought about a cam problem. I had a second good working carb on this engine with the same running results.

11-07-2002, 09:34 AM	#5
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,269	Pull your HEI and bring it to any auto parts pleace as most will test it for free--- at idle, at acceleration, at high speed, etc. Had one where the condenser would crap out--drove me nuts. Also had one where the weights would hit up against the bottom of the rotor and bid off---also drove me nuts. What size wire are you running to the HEI--should be heavier then stock to handle the HEI. You may want to run the HEI vacuum advance off of the timed vaccum port on the car verses the full manifold vaccum port or vice verse. If the engine has good compression, you've switched carbs, my guess is it's not internal and my $$ bet would be on one of the above. What does a vaccum gauge say at idle? Good luck

11-07-2002, 09:48 AM	#7
the-wreck Registered User Join Date: Sep 2001 Location: LI New York Posts: 159	Thanks guys for all your advice. You all are giving me some hope back. I will pull the distributor and look at it closely. The wire to the HEI is pretty heavy. I put in a M&H wiring harness that was made for HEI. The coil in it is new and we tried a different one witht the same results.

11-07-2002, 12:08 PM	#10
Yellow Cheyenne Registered User Join Date: Jun 2001 Location: Eastern Kansas Posts: 488	I watched a dyno session on a BB pontiac that sounds exactly as yours is doing. The engine hac been assembled by someone else a brought in to be dyno'd. Sounded very good at idle and would rev up good with no load. Once they would start the pull (actually load the motor), it would back fire and generally sound like crap. The problem ended up being that the cam timing was wrong. When they installed the chain, the gears were lined up on some other marks that were on the gears, not on the correct dots. Might want to check again because the symptoms sound very similar. At first glance, it looked correct on the Pontiac, closer observation revealed the problem. __________________ '72 Cheyenne. AC, PS, PB, Rear slider window, tilt. Light yellow (grapefruit yellow according to new sales literature from '72) '56 Chevy short step V-8 (My dad bought it new!!) '70 Olds 442 convertible '70 Olds Rallye 350

11-07-2002, 03:10 PM	#11
John Fabris TOTY 2006 Join Date: Dec 1999 Location: Magalia CA USA Posts: 2,270	From reading all of this, no one has mentioned PLUG WIRES. If the engine idles fine, and in Park or Neutral you are able to rev the engine with no problems, but then when you put a load on it, meaning you put it into drive and the give it gas and it starts to run like crap, then it is most likey bad plug wires. __________________ John Fabris 67 C10 SWB

11-07-2002, 04:33 PM	#12
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	if you had a 3 key timing gear..and used the wrong mark..diamond or square instead of circle..then the cam would either be retarded or advanced 4 degrees...this would not cause t he problems your having..all it does is lower or raise the rpm range..Im still betting on the mechanical advance or plug wires jim __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA

11-07-2002, 05:07 PM	#13
the-wreck Registered User Join Date: Sep 2001 Location: LI New York Posts: 159	Big- Do you think a mechanical advance malfunction could give me a problem like this? The MSD plug wires were right out of the box....so chances of them being bad are pretty slim I think.

11-07-2002, 06:52 PM	#14
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,403	im not Big, Im Crazy.....but yes if the mechanical advance is stuck it will cause problems like you have & that is a common prob on the HEI's __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

11-07-2002, 07:39 PM	#15
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	yea..what crazy said..happens all to frequently....its easy to diagnois though...just unhook the vacuum advance and plug the line...put a timing light on it and rev it up...how much does it advance..any?? that will eliminate or find the problem jim __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA



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11-09-2002, 08:15 PM	#16
lugnuts Registered User Join Date: Nov 2002 Posts: 13	It sounds like something that happend to me when I changed the intake on my 327. I put a perfromer on it and and it ran the same way idle & part throttle it ran fine but when i would get in it , it would spit and sputter & it turned out to be the intake gasket, I changed them and it fixed my prob.

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