Help lost with tuning adjustments
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Help lost with tuning adjustments
I have a 78 Ford Bronco 351M no emissionsand C6 trans. I have MSD 6a, blaster 3 coil, 8580 dizzy (mechanical advance), Edelbrock cam, carb (1406), intake (no egr). I have my timing set at 12 btc with my mechanical advance at 21 degrees in by 3000 rpms (blue springs and blue stop). My carb is still at factory settings because I have no idea were to start on jetting. Plugs are brownish grey color. My problem is when I give it hard throttle from dead stop it falls on its face (sometimes pops thru carb) then comes back and dosnt always feel very strong. I run at least 92 octane always. Ive put a fuel regulator on it and have it adjusted to 5.5 psi. Im so LOST I could scream. I dont have a lot of experiance with carbs. By the way the exhaust smells rich when I jump on it. Any help would strongly apperciated.Ive listed every thing I culd think of. Thanks in advance.
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Your timing is all wrong. Running a mechanical advance only distributor is never going to work right on the street. They are for full throttle racing only. Get a distributor with vacuum AND mechanical advance. A stock compression 351M does not need premium fuel. Premium fuel will degrade performance and mileage.
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From: iowa
Eric hates pure mechanical advance distributors. 
you can run them on the street, they may not be 100% the absolute best for every situation but they will run just fine, I have run them in the past, probably would again without any problems, your problem isn't in teh timing, it's almost certianly a fuel related issue.
you can run them on the street, they may not be 100% the absolute best for every situation but they will run just fine, I have run them in the past, probably would again without any problems, your problem isn't in teh timing, it's almost certianly a fuel related issue.
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Posting Legend
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I dislike them because they do not work well on the street. You can get them to "work" but that is about all. Get a proper distributor or live with poor performance, stumbling, pinging, backfiring, black pipes, fuel costs out the wazoo, -your choice. You can pay for the proper distributor with a few tanks of wasted fuel. Premium fuel is not required. Your timing numbers are still WAY off.
"If it's not broke modify it until it is." -I think he is past this point....
"If it's not broke modify it until it is." -I think he is past this point....
Last edited by Torque1st; Apr 15, 2007 at 02:57 PM.
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From: iowa
Premium fuel should not be required or even wanted by that motor. I still think most of your problem is with the accelerator pump on the carb.
Don't worry about base timing, total timing is more important to start with, somewhere around 34-36 max is where I start with and adjust from there if needed. Also you might want to check that your timing marks are actually accurate, some dampeners can slip and be off causing you to be way off on your timing.
Don't worry about base timing, total timing is more important to start with, somewhere around 34-36 max is where I start with and adjust from there if needed. Also you might want to check that your timing marks are actually accurate, some dampeners can slip and be off causing you to be way off on your timing.
Last edited by monsterbaby; Apr 15, 2007 at 02:59 PM.
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Start here with the right distributor:
-----------------------------------------
Centrifugal Advance Start: 0-0.5° @ 350RPM Finish: 14° @ 2275RPM
Vacuum Advance Start: 0-1° @ 5" Finish: 12.5° @ 25"
Initial Timing: 10° BTDC.
Vacuum given in inches of Mercury (Hg).
RPM specified as distributor RPM.
Degrees specified as distributor degrees.
---------------------------------
Double those values for crankshaft figures:
Example: 0-0.5° @ 350RPM distributor becomes 0-1° @ 700RPM on the engine.
-----------------------------------------
Centrifugal Advance Start: 0-0.5° @ 350RPM Finish: 14° @ 2275RPM
Vacuum Advance Start: 0-1° @ 5" Finish: 12.5° @ 25"
Initial Timing: 10° BTDC.
Vacuum given in inches of Mercury (Hg).
RPM specified as distributor RPM.
Degrees specified as distributor degrees.
---------------------------------
Double those values for crankshaft figures:
Example: 0-0.5° @ 350RPM distributor becomes 0-1° @ 700RPM on the engine.
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From: iowa
Originally Posted by Torque1st
I dislike them because they do not work well on the street. You can get them to "work" but that is about all. Get a proper distributor or live with poor performance, stumbling, pinging, backfiring, black pipes, fuel costs out the wazoo, -your choice.
Posting Legend
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Centrifugal or mechanical advance is for full throttle full load advancing the timing to make up for engine speed.
Vacuum advance is your load and mixture dependent timing mechanism to make up for lean mixtures not burning as fast etc.
You need both to operate at varying load/throttle positions.
Compromising is what the two advance mechanisms do.
I have seen many straight mech advance distributors running over the years and they are all a compromise to get them to work. Much better performance can be obtained with a proper distributor.
Even computer equipped vehicles have both load and RPM dependent timing maps in them. But of course that does not work well. The OEMs should just use RPM only...
Vacuum advance is your load and mixture dependent timing mechanism to make up for lean mixtures not burning as fast etc.
You need both to operate at varying load/throttle positions.
Compromising is what the two advance mechanisms do.
I have seen many straight mech advance distributors running over the years and they are all a compromise to get them to work. Much better performance can be obtained with a proper distributor.
Even computer equipped vehicles have both load and RPM dependent timing maps in them. But of course that does not work well. The OEMs should just use RPM only...
Last edited by Torque1st; Apr 15, 2007 at 03:13 PM.
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Joined: Dec 2003
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From: iowa
I will try one more time, Read the problem stumbles when stabbing throttle off idle, that is NOT timing that is accelerator pump. Off idle stumbles make ABSOLUTELY no difference which dist you are running, problem is once again NOT timing unless the initial timing is WAY off.
Last edited by monsterbaby; Apr 15, 2007 at 03:15 PM.