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Old 11-07-2010, 09:57 PM
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40 degrees advanced timing to run

I'm not real good with Chevy BB engines but we were working on my friends BB Chevy trying to get it to run better. He has a new distributor which is electronic ignition (don't know the name) We put the engine on TDC, placed the distributor to #1. and fired it up. The engine should run well but we have advance the heck out the timing to get it to run decent. The engine runs fine at 40 deg or more of advanced timing . We pulled the plugs and each cylinder is reading 150lbs compression and plugs are burning a little on the rich side( not black). The vacuum at idle is around 5-7 lbs. We've tried moving the distributor and nothing works. The engine is a dog all the way to 4000 rpm and we haven't pushed it further than that. We're running a 850 Edelbrock carb on it. We are baffled by this engine...Any suggestions on what to look for besides pulling the camshaft and timing gear?

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Old 11-07-2010, 10:15 PM
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You sure you're not one tower off on the cap? Timing it with vac adv disconnected and plugged?

What all was done to the motor?
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Old 11-08-2010, 01:40 AM
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What camshaft is in this motor?
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Old 11-08-2010, 01:43 AM
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nova has a good point, it sounds a little bit like you set the timing with the vac. advance connected.

I don't mean to insult you, but make sure you've got the right plug wire!!! I've run into that working on a car at the shop.. the plug wires were a rats nest of wires that were 5 miles too long.. and I managed to hook onto the #3 wire instead of the #1 wire and couldn't figure out why the timing light was showing some ignorant numbers!!! after doing some head scratching and double checking I found the problem

one other thing.. your new distributor.. it's not "Locked out" is it? (mechanical advance disabled) ???

My MSD ProBillet can be run either way, and I bought it used, and it was locked out when I got it..
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Old 11-08-2010, 05:16 AM
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Need to know what the cam specs are and knowing the compression ratio will help as well. If it idles like crap, i.e. "choppy", you might have a big cam that may well need a ton of advance to idle and run right- but w/o knowing what you've got, it's all guesswork.
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Old 11-08-2010, 08:05 AM
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How did it run before the dist. change? If it ran well you need to go back to square 1. re-verify TDC and do it over. If your convinced your doing it right, Blame the dist.
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Old 11-08-2010, 08:34 AM
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The car was purchased recently and came with the motor. The story is the motor came out of a boat. We don't know who built it or how it was built (for blower, turbo, etc) The guy had it built for the boat, after taking it out on the water, he decided he wanted a "bigger" motor with more horsepower for the boat. They pulled the engine and put it in the 56 Chevy wagon. The problem is we don't know what cam is in it, nor what type of timing chain or how it's set up. We did have the vacuum advance disconnected and vacuum hose plugged from the carb, and we did use #1 cylinder with the timing light. Several friends were trying to figure this out who have years of experience working with engines.etc. And we are stumped!!! Were hoping its something simple we are overlooking and not having to pull the engine apart to see what cam is in it. Looking for different possibilities to a solution or maybe someone has had this problem as well. Thanks for the help all.

Last edited by kleen56; 11-08-2010 at 08:41 AM.
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Old 11-08-2010, 08:49 AM
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Was this motor built for a Ski boat with headers?

The 5-7 "s manifold vacuum at idle indicates a big cam.
Assuming its fireing on all 8 cylinders a big cammed motor needs a ton of idle advance cause of the egr effect at idle of the cam overlap.

Lock out the advance curve and set at 38 BTDC.

Big cammed motors also need more air flow at idle.
The Qjet has tiny primary throttles and only passes a small amount of air at idle. If the PCV is eliminated all the worse.
Hook up the PCV so it is functional. This will give some of the extra needed air flow at idle. Additional air flow can be gained by creating a adjustable bleed using a aquarium pep **** tee 'ed inot the pcv line going to the base of the carb.
You need the correct balance of air flow thru the carb throttles and PCV and air bleed pep **** at idle. The carbs pri throttles must be in the "sweet spot" at idle. (correct idle transfer slot exposure.) If the throttle is too far open at idle, the idle circuit and off idle response will be crappy.
The primary metering rod power piston spring will needed to be swapped for a light tension/(low vacuum rated) spring so the meterinig rods are down/lean at idle. (edelbrock service part)
Do not drill the throttle blades to gain idle air flow.
Its not nessessary. The extra idle timing and PCV and adjustable idle air flow air bleed will correct the idle.

Measuring the cam lift off the pushrod tip of the rocker arm (using a dial indicator) will give you a good idea of the cam.

When you have made these changes it will idle clean and the throttle response will be much better. A high stall converter is required.

Last edited by F-BIRD'88; 11-08-2010 at 08:57 AM.
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Old 11-08-2010, 08:59 AM
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Replace the spark plugs if they are fouled. Make sure you have the correct spark plug type/reach for the cylinder heads used.
If HEI distributor make sure its getting a full 12VDC and the motor is grounded to the firewall.

Make sure the OEM GM rear starter mounting brace is installed on the
starter motor when using locked out timing.
If its missing get one and install it.
If the motor is hard to restart when hot with locked timing
install a simple ignition power interupt switch.
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Old 11-08-2010, 09:42 AM
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You should verify that what you are seeing at the damper and timing tab for TDC is actually TDC.
DETERMINING TDC will allow you to be sure the timing tab and damper are correctly indicating TDC.

MAKE A TIMING TAPE to see what the total timing is, w/o needing to use a dial back timing light. You can also buy a timing tape, they're not very expensive. The problem is if you have a different diameter damper than what the timing tape is made for.

If you use a mechanical advance, be sure the advance plate is free to move, w/o binding or friction. HERE'S an exploded view of an HEI distributor. THIS is a description of an HEI rebuild.

I would recommend that you use the vacuum advance, hooked to manifold vacuum. It should be limited to around 10 of added advance. This will help keep the carb primary blades from being opened too far to get the idle speed where it needs to be. If the blades are opened too far, the idle quality and off idle response will not be good.

You may well need an adjustable vacuum advance to get the advance at a low enough vacuum, given the lack of idle vacuum you now have. Using the vacuum advance should help bring up the idle vacuum as well.

If the vacuum advance you have comes in OK but gives too much advance, you will need to physically limit the vacuum advance can's travel w/a vacuum advance limiter plate like the Crane #99619-1, #99619 Instructions.
Or you can easily make one.

Crane has an adjustable vacuum advance can kit- Crane #99600-1, #99600-1 Instructions.

The Accel #31035, #31035 Instructions is an adjustable vacuum advance can for GM HEI that is said to allow infinite adjustment to both the amount and rate of advance. Comes w/instructions and tool.
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Old 11-08-2010, 09:35 PM
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Cobalt and everyone, thanks for the great advice. I'm forwarding this information to my friend and I'll be posting the outcome later on.
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