Carb adjustment after ignition advance - Chevelle Tech
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post #1 of 36 (permalink) Old May 28th, 20, 5:54 AM Thread Starter
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Juan Ma
 
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Carb adjustment after ignition advance

Hello everyone!

I have been doing adjustments on my 454 engine because the idle was unstable when hot.I have a Quick Fuel BR-67213 BRAWLER 750 CFM MECHANICAL SECONDARY. I have been reading a lot about it, but I have several questions. This is the way that I have used to adjust ignition advance and carb.

1. I set the ignition advance on 8 degrees. Most of the post said that 8-12 it's enough for a stock engine, but I don't know how is the correct ignition advance for me.

2. I turn off the engine. I set the mixture on carb, one and a half out from the bottom.

Engine doesn't start.

I have to set all mixture screws only half turn from the bottom. I think that only half turn it's no enough for a big block, isn't it?

Other way to start is setting idle high. By this way the vacuum value is over 20 PSI. I don't know when it supposes that I have to check highest vacuum.

3. Engine running and warm. With 8 degrees I have to use only half turn on all screws mixture. If I want to set one complete turn I have to set 12 to 16 degrees in order to get the highest vacuum value.

Why this happens??

Should I set again the ignition advance at this point?

4. Most of the times, if I set all the mixture screws the same amount the vacuum goes down. Where I should to start? Primary or secondary mixture screws?

In a nutshell, I don't know the order to set a perfect adjustment for ignition advance + carb.
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post #2 of 36 (permalink) Old May 28th, 20, 7:37 AM
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Jeff
 
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Re: Carb adjustment after ignition advance

Disconnect the vacuum advance and leave it that way.

Keep adding initial timing until its either hard to start or pings at full throttle.

If 9.5:1 compression or lower use 87 octane if 10:1 or higher use 93.

Use a 180 thermostat.. If you have heating issues try a 160 thermostat. I find my motors run best with the 180..

I have a very low mileage stock 1978 454 low compression truck motor with 781 heads. My motor likes 20 degrees initial with 16 mechanical all in by 2500 rpm.. You want your timing to be fully advanced at cruising rpm at 35 mph..
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post #3 of 36 (permalink) Old May 28th, 20, 8:09 AM
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Eric
 
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Re: Carb adjustment after ignition advance

What distributor are you running?

You're just jealous because you can't hear the voices!

1967 Olds Cutlass 468 BBC/T400
1963 Plymouth Fury 440/Torqueflite
2007 Ford Mustang GT (momma's car)
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post #4 of 36 (permalink) Old May 28th, 20, 9:07 AM Thread Starter
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Juan Ma
 
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Quote:
Originally Posted by hydro462 View Post
Disconnect the vacuum advance and leave it that way.

Keep adding initial timing until its either hard to start or pings at full throttle.

If 9.5:1 compression or lower use 87 octane if 10:1 or higher use 93.

Use a 180 thermostat.. If you have heating issues try a 160 thermostat. I find my motors run best with the 180..

I have a very low mileage stock 1978 454 low compression truck motor with 781 heads. My motor likes 20 degrees initial with 16 mechanical all in by 2500 rpm.. You want your timing to be fully advanced at cruising rpm at 35 mph..
I have disconnected the vacuum advance and plugged with a screw.

I don't know the compression ratio and here, in Spain only have 95 and 98.

How could I know the perfect ignition advance for street?

Quote:
Originally Posted by oldcutlass View Post
What distributor are you running?
Hei Stock distributor
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post #5 of 36 (permalink) Old May 28th, 20, 10:01 AM
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Re: Carb adjustment after ignition advance

why does that wiring look wrong to me???
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post #6 of 36 (permalink) Old May 28th, 20, 10:04 AM
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Bart
 
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Re: Carb adjustment after ignition advance

Quote:
Originally Posted by hydro462 View Post
My motor likes 20 degrees initial with 16 mechanical all in by 2500 rpm..
Do this first and you will find it a WHOLE lot easier to get it running right....
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post #7 of 36 (permalink) Old May 28th, 20, 10:12 AM
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Re: Carb adjustment after ignition advance

I hope those numbers on the cap arent for the cylinders...

72 SS 402/4 speed/Straub roller and a bunch of Duramaxes.....
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post #8 of 36 (permalink) Old May 28th, 20, 11:37 AM Thread Starter
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Juan Ma
 
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No. They aren't for cylinders, don't worry about it
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post #9 of 36 (permalink) Old May 28th, 20, 5:09 PM
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Re: Carb adjustment after ignition advance

"Disconnect the vacuum advance and leave it that way."

"Keep adding initial timing until its either hard to start or pings at full throttle."

Just when will the flood of extreme misinformation from this one poster come to an end? It is dead wrong.
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post #10 of 36 (permalink) Old May 28th, 20, 11:08 PM
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What year vehicle is this in? Just curious if you have a full 12 volts to your distributor. If you're using a factory resistor wire for points ignition to that HEI, it's not going to run correctly.
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post #11 of 36 (permalink) Old May 29th, 20, 9:13 AM Thread Starter
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Juan Ma
 
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Quote:
Originally Posted by Dave Ray View Post
"Disconnect the vacuum advance and leave it that way."

"Keep adding initial timing until its either hard to start or pings at full throttle."

Just when will the flood of extreme misinformation from this one poster come to an end? It is dead wrong.
The vacuum is disconnected and sealed. I add ignition advance until idle goes rough but, my doubt:

With 8 degrees and half turn on the mixture screws idles goes fine, with 16 degrees and one complete turn on mixture screws seems good too. What it's better?

Is normal only half turn on mixture screws?? Instructions sheet said that to must one and a half turn at first, then do adjustments.

Quote:
Originally Posted by Johnny Bravo View Post
What year vehicle is this in? Just curious if you have a full 12 volts to your distributor. If you're using a factory resistor wire for points ignition to that HEI, it's not going to run correctly.
At the distributor coil goes 12v, direct from battery, with a anti-thief switch. Should I replace it for another? For instance, electronic msd distributor?
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post #12 of 36 (permalink) Old May 29th, 20, 10:04 AM
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Re: Carb adjustment after ignition advance

Quote:
Originally Posted by hydro462 View Post
Disconnect the vacuum advance and leave it that way.
Do this if you want your car to run like crap. Otherwise, disregard.....
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post #13 of 36 (permalink) Old May 29th, 20, 10:30 AM Thread Starter
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Juan Ma
 
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Quote:
Originally Posted by Georgia69 View Post
Quote:
Originally Posted by hydro462 View Post
Disconnect the vacuum advance and leave it that way.
Do this if you want your car to run like crap. Otherwise, disregard.....
I disconnected it only for adding ignition advance, after that I plug it again in the distributor vacuum advance

Last edited by kanij0; May 29th, 20 at 10:49 AM.
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post #14 of 36 (permalink) Old May 29th, 20, 11:12 AM Thread Starter
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Juan Ma
 
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Would it be a good improvement a electronic Ignition Distributor Coil ready to run??

Something like that? An electronic distributor without ignition box.
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post #15 of 36 (permalink) Old May 29th, 20, 11:17 AM
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Mike
 
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Re: Carb adjustment after ignition advance

We don't know much about your engine (what camshaft you have, for example) but I've used fancy ignition systems in the past and honestly I think a GM HEI is the best. It looks like this is what you have already from the photos.

Mike

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