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#5842247 - 11/23/11 04:43 PM Re: Anybody familiar with old Chevy big blocks? [Re: thetrio]
BillyGoatGruff Online   content
Campfire Guide

Registered: 11/16/08
Posts: 4938
Loc: North Central MT
More good help, thanks. I went out last night with the intent of pulling the cap checking for good connections and pulling wires and checking them. I said why the heck not and tried to start it, and I'll be darned if it didn't fire right up. So I took it out for a spin and she ran like crap, about died several times. Didn't want to idle, sounded rough too when it was running. After filling the shop with fumes, I figured I'd get after it again this weekend when I have time. If it is a timing issue I guess I'll have to take it in somewhere. I got the names of a few mechanics in town today.

And I'll definitely be exploring an electric fuel pump this summer, as the clearance is not confidence inspiring.

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#5842386 - 11/23/11 05:20 PM Re: Anybody familiar with old Chevy big blocks? [Re: BillyGoatGruff]
bethalhntr Offline
Campfire Regular

Registered: 07/25/11
Posts: 454
Loc: The Evergreen State.
Make sure and check for vacuum leaks, That could be your rough idle. Vacuum lines at the carb and make sure your carb bolts are snuged down good. Normally a chev will have a Quadrajet, If you have a carter afb there might be a spacer between the intake manifold and the carter, You might find the problem there. Best of luck, Deen.

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#5858937 - 11/28/11 11:48 PM Re: Anybody familiar with old Chevy big blocks? [Re: BillyGoatGruff]
Bull_Elk Offline
Campfire Regular

Registered: 05/03/03
Posts: 1051
I have an 85 3/4T Suburban with a 350 and about every 3 or 4 years I find myself changing the ignition module in the distributor. The first time it went out I was pulling a hill and I didn't think it would make it over the top. Took it to the dealer the next morning and because it cooled down overnight, it ran like a champ. They changed the module on a hunch and it ran great for a couple years until one day it didn't have the power to pull itself from a wet paper bag. Changed the module and off and running again. I've seen them act up when hot or just fail entirely. I carry a spare in the glove box with a phillips screw driver and a 1/4" nut driver. Depending on the vintage of your distributor, this could be an issue for you too.
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#5861979 - 11/29/11 06:57 PM Re: Anybody familiar with old Chevy big blocks? [Re: Bull_Elk]
BillyGoatGruff Online   content
Campfire Guide

Registered: 11/16/08
Posts: 4938
Loc: North Central MT
Thanks for the help and ideas guys. So now in the last couple days I got a fuel pressure gauge and regulator. I put the gauge in first and it read at 8 psi, which from what I've found is within the range it should be, but I figured I had the regulator so I tried it. I put it on wide open and it read over 9 psi and with it running I cranked it down to 6 psi, but no change. It still ran poorly. So I pulled them off and ran the fuel line directly from the pump to the carb again. I pulled the wires and cap, and I did find one wire that was all corroded up at the clip where it snaps over the plug. So I replaced that one and a couple others that were sitting too close to the headers with wires that had 45 degree booties. I also replaced the ignition module. One thing to note is that all 8 of the plugs were carboned up really bad, as in it wouldn't just wipe off on my coveralls, I had to scrape it off with a knife.

So tonight with a new module, and good plug wires I tried her again. She fired up and idled, but didn't sound quite right. At higher rpm is sounded better/smoother, but at idle it wasn't a purr. I can't really describe it but it just didn't sound right. I took it out and drove it around for about 10 minutes and it just got worse, to the point it stalled. To get it to start I had to floor the accelerator and wait and after a few seconds the rpms picked up and I limped it back in the shop.

I think I've now exhausted all I can do with my limited knoweledge myself. A buddy offered to let me borrow a timing light, but I don't know how the heck to work on timing. When I pulled the cap off the connection points inside had a little buildup, but nothing that didn't scrape off pretty easy. The wires do look pretty old and it was a little rusty in there.

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#5862210 - 11/29/11 07:43 PM Re: Anybody familiar with old Chevy big blocks? [Re: BillyGoatGruff]
walt501 Offline
Campfire Regular

Registered: 12/20/10
Posts: 807
Loc: Minnesota
Do you have an exhaust back pressure valve? That's not the correct name, but I can't remember what it used to be called. Anyway, it should be located right where the exhaust manifold meets the exhaust pipe at the rear of the engine, usually on the passenger side. It looks like a spring with a weight attached, and you should be able to rotate the weight by hand. Its purpose is to hasten engine warmup, but if they become stuck they cause all manner of drive-ability problems. If you can't rotate the weight, try spraying some penetrating oil on it and leave it sit overnight.
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#5862238 - 11/29/11 07:48 PM Re: Anybody familiar with old Chevy big blocks? [Re: walt501]
BillyGoatGruff Online   content
Campfire Guide

Registered: 11/16/08
Posts: 4938
Loc: North Central MT
Hmm I'll check tomorrow, but I don't think so. I believe it's just headers straight back to the mufflers and tailpipes.

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#5862245 - 11/29/11 07:49 PM Re: Anybody familiar with old Chevy big blocks? [Re: walt501]
ken458 Offline
Campfire Regular

Registered: 03/09/09
Posts: 781
Loc: west coast of AZ
Originally Posted By: walt501
Do you have an exhaust back pressure valve? That's not the correct name, but I can't remember what it used to be called. Anyway, it should be located right where the exhaust manifold meets the exhaust pipe at the rear of the engine, usually on the passenger side. It looks like a spring with a weight attached, and you should be able to rotate the weight by hand. Its purpose is to hasten engine warmup, but if they become stuck they cause all manner of drive-ability problems. If you can't rotate the weight, try spraying some penetrating oil on it and leave it sit overnight.

I believe he mentioned that he has headers, which would eliminate the exhaust back pressure valve of the stock exhaust manifolds.

I would go on eBay and order up a $48 delivered NEW HEI distributor, and buy a new set of wires and spark plugs and install it. I bet that fixes your problem.
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#5862419 - 11/29/11 08:46 PM Re: Anybody familiar with old Chevy big blocks? [Re: BillyGoatGruff]
358Norma_fan Offline
Campfire Regular

Registered: 11/04/09
Posts: 820
Loc: Anchorage Ak
Originally Posted By: BillyGoatGruff


So tonight with a new module, and good plug wires I tried her again. She fired up and idled, but didn't sound quite right. At higher rpm is sounded better/smoother, but at idle it wasn't a purr. I can't really describe it but it just didn't sound right. I took it out and drove it around for about 10 minutes and it just got worse, to the point it stalled. To get it to start I had to floor the accelerator and wait and after a few seconds the rpms picked up and I limped it back in the shop.

I think I've now exhausted all I can do with my limited knoweledge myself. A buddy offered to let me borrow a timing light, but I don't know how the heck to work on timing.


Sounds like you might have a carb problem. It sounds like it's running rich and loading up, hence the having to hold the pedal to the floor then clearing up. Needle and seat may be worn or the floats are bad.

Highly recommend getting the timing light and checking to see where the base timing is, as well as making sure the advance is working. I don't remember what base timing should be off the top of my head, but a chilton manual will have it as well as instructions on how to check the timing.
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#5865348 - 11/30/11 04:35 PM Re: Anybody familiar with old Chevy big blocks? [Re: BillyGoatGruff]
tzone Offline
Campfire Oracle

Registered: 02/23/04
Posts: 28219
Loc: MN
Bad plugs, wires, cap, rotor/points can make a motor do funny stuff.

With all that carbon build up, it sounds like it is a timing or fuel problem. When you had the timing adjusted the first time, it may have helped, but with the mixture of carbon, bad wires, and crusty points, it may be wigged out again.

I'm far from an expert on this stuff. It sounds to me like you're checking the right stuff.
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#5865608 - 11/30/11 05:35 PM Re: Anybody familiar with old Chevy big blocks? [Re: tzone]
BillyGoatGruff Online   content
Campfire Guide

Registered: 11/16/08
Posts: 4938
Loc: North Central MT
I'm going to dive into the carb this weekend. Never looked in one before, always thought they required voodoo to understand/work on. But heck, I'll learn something, probably quite a bit, and if I can get her cleaned up and maybe rebuilt it'll help. I won't get the timing light from my buddy for a couple weeks probably so I'll do this in the mean time.

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