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Old 11-09-2009, 07:55 AM
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Stock 350 Road Demon Tuning

Hello
I have a 1976 Chevy k10 with
350 stock replacement crate engine
Stock cam????
Road Demon 625
Accel HEI
K&N air filter
Edlebrock performer intake
Headers

I just picked the truck up it was not running when I got it.
I reset the distributer and put new plugs in it and it fired right up
(the old plugs had fouled)
With it running it seemed really rich at idle and into part throttle
But if I advanced the timing (a lot) it would run much better (like a lot)
Since then it fouled the plugs again and I cleaned them up and it
ran the same. I have new plugs for it but I don’t want to put them in
just to have to buy more with no progress???

Now with the timing set a 15*
The secondary butterflys fully closed
and .20 on the primaries
All I can get is 3/4 of a turn out on all four before the vacuum drops and the engine starts running rough so all I can get is 15 inches and I can’t even change that very much???
The 15 is with the vac advance hooked up with a T

Should it be higher than that and should I be able to tune it with a broader range before the engine wants to die???

I have read a bit about people drilling out air bleads and changing feed screws but I dont want to mess anything up????


Thanks

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Old 11-09-2009, 01:34 PM
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Demons don`t tune like regular carbs, that`s why it`s important they be tuned by the booklet that comes with them. Next up, lets reset the timing. With the vacuum advance disconnected and plugged, set the timing to 12 degrees before top dead center, lock the distributor and reconnect vacuum advance, make sure you connect it to a full time manifold vacuum source, (which is any source that pulls vacuum full time, even at idle) the timing should then be 20-24 degrees before top dead center at idle. Set the idle mixture with a vacuum gauge, set it to its highest vacuum reading. You can call barry grant and get a booklet for your demon that will tell you how to tune it.
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Old 11-09-2009, 02:05 PM
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Thanks DoubleVision
I can try it a 12*, the 15* was with vac adv disconected
My main question is what kind of vacuum range should I have when setting the idle mixture?? should I have more than 15"
and should I have more of a range before the engine runs rough???
like adjusting down to 11" then back up to 15"?
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Old 11-09-2009, 03:24 PM
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The manual reckons 18º-24º advance, might help starting there.
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Old 11-09-2009, 03:33 PM
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18-24* is for performane applications
I thought my app was kind of on the stock side????
could be wrong
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Old 11-09-2009, 03:50 PM
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Suck it and see.
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Old 11-09-2009, 05:47 PM
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If you set the timing the way I instructed already makes the timing that high at idle, and it works for both stock and performance engines.
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Old 11-09-2009, 06:12 PM
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You cannot clean gas fouled plugs, they will keep fouling no matter what.
The other 2 guys DV & Malc are correct on the timing & carb.
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Old 11-10-2009, 05:36 AM
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malc sorry I didnt read the advance part

I should be there I will try 12 instead of 15 and see if that helps

what about

My main question is what kind of vacuum range should I have when setting the idle mixture?? should I have more than 15"
and should I have more of a range before the engine runs rough???
like adjusting down to 11" then back up to 15"?
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Old 11-10-2009, 10:48 AM
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"I should be there I will try 12 instead of 15 and see if that helps"

The manual reckons 18º-24º advance, might help starting there.
So why go to 12º you need to try upping it ?

"The secondary butterflys fully closed and .20 on the primaries"

The manual states, both should be open the same amount.
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Old 11-10-2009, 01:14 PM
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Base of 12 degrees without vacuum advance connected, then connect it to a full time manifold vacuum source that pulls vacuum even at idle will put the base timing at 20 to 24 degrees which is where the book recommends it to be.
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Old 11-10-2009, 01:29 PM
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malc I am setting it the way DV states
Is that is the same as what you are trying to say?

It is at 15* base then plug the advance in!!!
So I will try 12

I closed the rear transfer slot more because it was still to rich to adj at idle????

Thanks for all the replys just bare with me I am just trying to get this right
Jeff
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Old 11-10-2009, 01:42 PM
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Disconnect your vacuum advance, plug the carb connection.
Now time the motor, idling 500 more or less to 18º, that is your initial timing.
Return your idle speed to 750, I find that acceptable, reconnect your vacuum
advance then try your carb tuning again.

Have a read of this and this.
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Old 11-11-2009, 08:43 AM
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Quote:
Originally Posted by malc
Disconnect your vacuum advance, plug the carb connection.
Now time the motor, idling 500 more or less to 18?, that is your initial timing.
Return your idle speed to 750, I find that acceptable, reconnect your vacuum
advance then try your carb tuning again.
Malc has it the same as what I suggest also.

Use full manifold vacuum when it is connected.

Idle RPM of 650-800 should be with the trans in DRIVE if an automatic or NEUTRAL if a standard shift. It will increase 150-200 RPM when the auto trans is placed in PARK. The reason to keep the RPM below 800 is so that no centrifugal advance is being introduced.

NOTE: Be sure to block the drive wheels and have the emergency brake fully applied when checking this in gear. I also suggest having a helper with their foot on the brakes as well. Do NOT rev the engine when checking with the trans in gear.

Your TOTAL mechanical timing with no vacuum added should be all in around 2500-3000 RPM and should not exceed 40 degrees. 32-34 degrees is suggested for Vortec heads and 36-38 degrees otherwise.
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Old 11-11-2009, 10:18 AM
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Maybe I missed something here, 18 degrees with no vac advance, then you connect it using a full time manifold source as we all suggested will put the base timing at idle to 30 degrees. When directly off idle with high vacuum conditions when centrifical advance comes on it`ll be advanced over 46 degrees and higher depending. Unless he has dirt low compression I`ve never heard of any engine running this much advance without detonating itself to death in short order. Since I`ve never heard of it I ask to give me a better explanation on how it works, I`m always open to learn something new.
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