Timing and carburetor adjustments - Team Camaro Tech
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post #1 of 7 (permalink) Old Sep 1st, 14, 09:29 PM Thread Starter
Vick
 
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Timing and carburetor adjustments

68 camaro, 4 speed stick shift. Don't know much about the heads and what's under the covers as I acquired the car only few months ago and it's a work in progress. Carburetor is a Demon Road 625, Intake manifold Edelbrock Performer, Valve covers are Moroso and the following is what I got form the guy that sold me the car, I just copy everything as he wrote it: professionally rebuilt engine, decked and line bored, balanced, teflon coated skirt, flat top 10:1 pistons, cam, SS comp roller rockers & timing chain, ARP bolts, high volume oil pump.

Now the following is my issue. I've no idea where should the timing be on this one and the carburetor adjustment is another issue.

I idle between 600-700rpm, but the most I could get out of the vacuum is 15. The only time I get around 20 is when the idle is at 1000rpm. With the timing set at TDC. If I advance the timing, RPMs go up, I lower them and the vacuum goes back down. I checked for leaks on both hoses - one from carburetor to valve cover and the other one from the intake manifold to the brake booster. No leaks. Also checked the carburetor on the intake manifold, no leak there, only thing I didn't check thoroughly for leaks are the valve covers, but they look great and from what I can see there are no leaks there.

I know one has to see the car to figure out what's going on as every classic car is different. Do you guys know any mechanic that really knows our cars and how to successfully adjust the timing and the carburetor? I'd really appreciate it. I live in the san fernando valley.
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post #2 of 7 (permalink) Old Sep 1st, 14, 10:37 PM Thread Starter
Vick
 
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Re: Timing and carburetor adjustments

I forgot to mention, it's a 350 small block
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post #3 of 7 (permalink) Old Sep 1st, 14, 11:04 PM
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Re: Timing and carburetor adjustments

Do you know the specification of the cam? Will the car idle where you have the timing set? Where are you setting the timing at?
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post #4 of 7 (permalink) Old Sep 1st, 14, 11:56 PM
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Steps
 
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Re: Timing and carburetor adjustments

u just set the mixtures and idle advance to your best stable idle...
that becomes your idle spec.
What really matters is when the car is moving...what advance and mixtures happen then...
Sort those specs out, then adjust the carb circuits , the cent advance and vaccuum advance to meet these specs.
There are many older posts on how to, the whys , the mods to the dizzy for non egr engines running HEI s.
Search function above.

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post #5 of 7 (permalink) Old Sep 2nd, 14, 12:14 AM Thread Starter
Vick
 
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Re: Timing and carburetor adjustments

I don't know any specs about the cam.
The timing is set at the TDC and it idles at 700rpms, the vacuum reading is around 15
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post #6 of 7 (permalink) Old Sep 2nd, 14, 04:40 AM
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Brian
 
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Re: Timing and carburetor adjustments

As stated you are setting a baseline tune at idle. And since you don't know the cam the vacuum may be all you will get with an aggressive cam.

The Old school tuning procudure I follow is:
Run engine up to operating temperature making sure the thermostat opens twice.

Shutdown engine and disconnect vacuum advance from the dizzy and plug the hose. Hook up your timing light and vacuum gauge on a manifold source - not ported. Restart engine.

Set idle at 700 or factory spec - 700rpm on my 69 manual 4-speed non-a/c L48.

Then I set timing with strobe to factory specs in the shop manual - dead TDC for mine.

Then I next adjust curb idle back to 700.

Then I use my vacuum gauge on a manifold source to find the best mix on the idler circuit adjustments one side at a time to get the maximum vacuum reading on the gauge.

One final check of the idle and timing with the light, then shut down and reconnect vacuum advance line and remove vacuum gauge.

Car purrs like a kitten at idle and is responsive all through the throttle range, and roars like a lion at WOT


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post #7 of 7 (permalink) Old Sep 2nd, 14, 06:28 AM
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Re: Timing and carburetor adjustments

I agree with everything 69 Pace said except on setting the timing to the specs in the shop manual. The man that sold you the car said the cam was changed so it might take a different setting. Once you have it running use a timing light with advance. Rev the engine to 3500 rpms and set the knob on the back of the timing light on 36 degrees. Adjust the distributor until the line on the balancer aligns with zero on the scale. You can rev the engine higher watching to make sure the line stays on zero. With a vacuum gauge adjust the idle mixture screws until you get the best vacuum reading. Set the curb idle to 700-750 rpms. How much vacuum you get for a reading depends on the camshaft specs. If you have 15 Hg I think that is good for an aftermarket camshaft. BTW you can reset the knob on the timing light to zero and check your initial timing but don't change anything. If you want to get into changing the initial timing and the mechanical (centrifugal) advance in the distributor read this article first. http://www.crankshaftcoalition.com/w...EI_distributor For setting timing start reading by clicking on number 14.
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