Timing and carb problem.....Can someone please help....? - Team Camaro Tech
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post #1 of 5 (permalink) Old May 23rd, 03, 07:51 AM Thread Starter
 
Join Date: May 2003
Location: Phoenix, AZ
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Question

Just incase I have lost my mind can someone please let me know what the timing marks are on a 350 Chevvy Camaro (1973) i.e. where is ATDC and BTDC in relation to Zero TDC on the timing cover mark? Where should the timing on this vehicle be set for optimum performance (motor is standard - no cam changes). Also, in setting the carburettor what would the best vacuum settings be?

It is running with an Edelbrock Performer Intake Manifold and a Edelbrock 1405 Carb.

Whenever we try to set the timing at 10 BTDC as one would suspect to be the right thing to do it absolutely runs like a dog and backfires through the carb. Yet, when you go the other way i.e. set it at 8 to 10 ATDC it runs like a charm. Timing should be good as the rotor lines up with #1 spark plug at TDC with piston at top and valves rocking.
Vacuum is pulling at 14 in. Hg. max (at 800 Rpm) and it smells very rich i.e. burns the nose and eyes. We have gone the leaner route by changing jets (Primaries 0.98 and secondaries 0.92. Metering rods are 070*052 at this stage with orange springs 5 in. Hg installed with them)

OK you timing and carb gurus out there, can you please help me out of my misery.....
Thanks for any and all help.

[ 05-24-2003, 10:45 PM: Message edited by: Z28_4_Mossie ]
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post #2 of 5 (permalink) Old May 24th, 03, 12:28 PM
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John
 
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Going counterclockwise on the timing tab, up from the "0" toward "A" (advance) is advanced; going down from "0" [img]graemlins/thumbsup.gif[/img] toward "R" (retard) retards the timing. Jets and rods don't affect idle mixture; that's set by adjusting the idle mixture screws to highest steady manifold vacuum reading, while adjusting the idle speed screw to maintain your desired idle rpm.

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post #3 of 5 (permalink) Old May 24th, 03, 01:24 PM
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Al
 
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Make sure you don't have a mismatched timing cover/balancer combo. There was a change in there around 1970.

Set your initial timing with the vac advance disconnected and plugged.


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post #4 of 5 (permalink) Old May 24th, 03, 07:42 PM Thread Starter
 
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Question

Thanks a stack guys, now at least I know I'm not losing my mind.
Per JohnZ I now know that my settings on the timing is correct and I suspect BPOS is completely correct in suggesting that the wrong/mismatched part might have been installed for the timing chain cover.
Now, I have got the timing dialed in and the carb has been set to give me the maximum stable vacuum (12-in.Hg., by the way should this not be a bit higher, say around 16 to 19-in.Hg? )
With that said and done the vehicle keeps on failing emissions on the idling part of the test and passes the loaded part of the test. What can I do to get the car leaned out a bit on the idling side [img]graemlins/clonk.gif[/img] ?
I'm thinking along the lines of changing the metering rod springs from a 5-in.Hg to a 7 or 8-in.Hg. Would this do it for the test or is there perhaps something else I could do to make this puppy pass..?
Thanks again for your valuable help and insight and I trust you will be having a blast of a weekend...!!
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post #5 of 5 (permalink) Old May 25th, 03, 06:44 AM
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John
 
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On the edelbrock, the idle mixture is completely controlled by the two idle screws on the front of the car I believe. Unless you are idling to the point that it is transitioning to the primary circuit.

John

- '68 Chevy Camaro (sort of done, but always subject to improvement)
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