Timing and Choke
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Junior User
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Timing and Choke
1976 f250 with 360 or 390. What should the Initial timing be and overall. There is no centrifugal advance but there is vaccum advance. I assume initial should be like 13 right but with the vacuum advance what should my overall be? Manifold or Ported vacuum. Ported for better mpg right? but will it reduce power? Also my manual choke will not pull out to choke the engine when cold like it's frozen or something. Any help is appreciated thanks!
Rusty Roller
Joined: Oct 2011
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From: Santa Cruz Mountains
I don't know what the initial timing is for "your" engine but it is set with the vac hose removed and plugged off. Then overall centrifugal and vacuum total advance is about 34 degrees or so.
The Vac is ALWAYS ported never manifold. There should be no vacuum "at idle" at the dist advance can.
You depress the gas pedal when setting the choke.
To check your centrifugal advance remove and plug the vac. Check with a timing light as you rev the engine. If your timing doesn't change you need to correct this problem. Rebuild or replace. For a engine (stock) to function correctly it needs/uses both systems; centrifugal and vacuum.
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The Vac is ALWAYS ported never manifold. There should be no vacuum "at idle" at the dist advance can.
You depress the gas pedal when setting the choke.
To check your centrifugal advance remove and plug the vac. Check with a timing light as you rev the engine. If your timing doesn't change you need to correct this problem. Rebuild or replace. For a engine (stock) to function correctly it needs/uses both systems; centrifugal and vacuum.
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MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
As OldStyle said, you do have to have the pedal down to load the choke; otherwise the fast idle linkage will pin the choke plate in place (assuming it's set up correctly). This is true even for a manual choke. If that's not the problem, then you'll have to have a look under the hood and see why it's binding.
Fleet Mechanic
Joined: Jun 2007
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From: Ohio
it could be more or less initial depending on the slot used.
To the OP, if there isn't any centrifugal advance then somethins wrong.
To the OP, if there isn't any centrifugal advance then somethins wrong.
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I set the initial timing to 16 is this too high? The overall was around 30. There is no centrifigul advance that i can see, could it be electrical. I guess I'll just have to check it with the timing light and the vac tube plugged. Why would you want both vac and centrifigul advance? Couldn't you be fine with just one.
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
16 degrees is too high, if it's really 16 degrees and not a slipped balancer. Make sure you're checking at the correct idle speed and the vacuum advance plugged off. If you have a stock distributor, you have a centrifugal advance. It's under the baseplate; you won't see it just by removing the cap. The distributor has to pretty much come apart. Vacuum advance is the large can outside of the distributor and easy to see. You'll have both.
For a stock engine, you want both centrifugal and vacuum advance. Centrifugal advance advances the timing based on RPM (spark has to happen sooner as engine spins faster). Vacuum advance advances the timing based on load (spark has to happen sooner as engine pulls). Both mechanisms are necessary for a street-driven vehicle.
For a stock engine, you want both centrifugal and vacuum advance. Centrifugal advance advances the timing based on RPM (spark has to happen sooner as engine spins faster). Vacuum advance advances the timing based on load (spark has to happen sooner as engine pulls). Both mechanisms are necessary for a street-driven vehicle.
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Junior User
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What is the highest I can safely go because it runs very well at 16 no pinging as far as i can tell. Is it hard getting to the centrifugal adavance?
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Rusty Roller
Joined: Oct 2011
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From: Santa Cruz Mountains
[quote= To check your centrifugal advance remove and plug the vac. Check with a timing light as you rev the engine. If your timing doesn't change you need to correct this problem. Rebuild or replace. For a engine (stock) to function correctly it needs/uses both systems; centrifugal and vacuum.[/quote]
Have you checked this yet? Without the vacuum attached to the dist and using a timing light. Rev the engine and see if the timing advances. Report back...
Have you checked this yet? Without the vacuum attached to the dist and using a timing light. Rev the engine and see if the timing advances. Report back...
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Junior User
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So I took the initial advance back down to 12 or 13. I plugged the vac advance and checked for centrifugal advance. It's not working. Could it just be corroded and stuck or hooked up wrong. Now, how do i get to it?
Fleet Mechanic
Joined: Jun 2007
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From: Ohio
are you just tapping the throttle, or going to 2000rpm+? If it's never been messed with, it will take a little while before it starts to advance, due to the springs delaying it.
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For a bone stock FE, initial is 6. But 8-12 works better. Total should be no more than 40, with 36-38 the sweet spot.
If it's true the centrifugal advance isn't working your performance and economy have got to be blowing goats. Something is jammed or stuck and it needs to be freed up for it to perform better.
Vacuum advance is for fuel economy. It also should be connected to a PORTED vacuum source and not full manifold vacuum.
Josh
If it's true the centrifugal advance isn't working your performance and economy have got to be blowing goats. Something is jammed or stuck and it needs to be freed up for it to perform better.
Vacuum advance is for fuel economy. It also should be connected to a PORTED vacuum source and not full manifold vacuum.
Josh
Rusty Roller
Joined: Oct 2011
Posts: 1,423
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From: Santa Cruz Mountains
If you take the distributor rotor and turn it by hand "lightly" it should rotate slightly and return. If not then something is jammed or broken. Find the obstruction, repair or replace with a rebuilt dist for 50 bucks or so.
It is also possible that the advance mechanism shaft is rusted. Under the rotor on top of the shaft is a felt disk. look under that. Oil lightly if necessary.
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It is also possible that the advance mechanism shaft is rusted. Under the rotor on top of the shaft is a felt disk. look under that. Oil lightly if necessary.
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Posting Guru
Joined: Oct 2010
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From: Missouri
Manifold vacuum and Ported vacuum are the same thing, except ported vacuum is not active at idle. Once off idle manifold and ported vacuum will have the same reading. Neither one is "for better mpg" you simply use which works better, which is normally ported when using a stock camshaft.