To much mechanical timing....?
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 990
Likes: 0
From: North Texas
To much mechanical timing....?
Ok well after spending an afternoon with Bubba on my back, I think I may have discovered the root of the problem. 
I have been having problems setting my max timing to 36º total in by 2500. After a few discussions with LARS, my HR cam is part of the problem (227/230 duration). So I run a B28 canister to get the car to idle.
Today, I finally got around to checking my total mechanical timing advance and I have 24º with a bushing. I think this is what is throwing me off.
It suppose to be 20º according to everything I've read. So, I don't have a welder. How can I fill in the slot so I can adjust the advance?
I have been having problems setting my max timing to 36º total in by 2500. After a few discussions with LARS, my HR cam is part of the problem (227/230 duration). So I run a B28 canister to get the car to idle.
Today, I finally got around to checking my total mechanical timing advance and I have 24º with a bushing. I think this is what is throwing me off.
It suppose to be 20º according to everything I've read. So, I don't have a welder. How can I fill in the slot so I can adjust the advance?
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 990
Likes: 0
From: North Texas
I have a Points style distributor. There is a slot that has pin which runs trhough it. This slot is used to determine the total mechanical advance. I have a brass bushing installed on the pin to limit the mechanical travel (advance).
Even with this setup, I have 24º of mechanical advance.
Basically, I can not get the car to idle in gear with the maximum timing set to 36º and 16º of advance using a B28 VC.
I think if I shorted up the mechanical advance to 20º from 24º and reset my maximum timing to 36º that would raise the inital timing by 4º.
Am I off base?
Even with this setup, I have 24º of mechanical advance.
Basically, I can not get the car to idle in gear with the maximum timing set to 36º and 16º of advance using a B28 VC.
I think if I shorted up the mechanical advance to 20º from 24º and reset my maximum timing to 36º that would raise the inital timing by 4º.
Am I off base?
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Something is not right here. You have 36 total and you say you have 24 mechanical so your initial is 12. The car should run OK with this. Now you also mention you have vacuum advance also. Is it hooked up to a ported or non ported. If it is manifold vacuum (non ported)the vacuum advance should be in at idle giving you approx another 12 to 16 degrees. This would give you a total of 24 to 28 degrees initial. This is approxamatly my setup and the car runs fantastic. I was not using vacuum advance before and the car was running OK but with the vacuum advance at idle it is more responsive and burns cleaner at idle. I agree you should have about 20 mechanical but the car should run OK with the setup you have.
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 990
Likes: 0
From: North Texas
Originally Posted by Gordonm
Something is not right here. You have 36 total and you say you have 24 mechanical so your initial is 12. The car should run OK with this. Now you also mention you have vacuum advance also. Is it hooked up to a ported or non ported. If it is manifold vacuum (non ported)the vacuum advance should be in at idle giving you approx another 12 to 16 degrees. This would give you a total of 24 to 28 degrees initial. This is approxamatly my setup and the car runs fantastic. I was not using vacuum advance before and the car was running OK but with the vacuum advance at idle it is more responsive and burns cleaner at idle. I agree you should have about 20 mechanical but the car should run OK with the setup you have.
Correct - 36 total with 24 mechanical does give me 12 inital. The car will not idle at 12 without the VC attached to manifold vacuum. With my B28, I get 16 additional which gives me about 28 at idle. The car will idle fine not in gear.
The car runs good but will not idle in gear at a stop.
I should add that this is not the stock motor. It's a 383 TFS heads and a Lunati HR 227/230 cam. I spoke to LARS and he said with that setup, I would probably have to connect to the manifold to get it to idle correctly.
Last edited by 1970-Bronze; Oct 22, 2005 at 06:33 PM.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
I have a cam with 248@ .050 duration and it will idle at 12 degrees initial. Not very well but it does run. Are you saying even with 28 degrees initial it will still not idle in gear? Are you running a real tight converter?
For a 383 motor that is not a huge amount of duration. It should run and idle in gear with that setup with the vacuum advance in at idle.
For a 383 motor that is not a huge amount of duration. It should run and idle in gear with that setup with the vacuum advance in at idle.
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Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 990
Likes: 0
From: North Texas
Originally Posted by Gordonm
I have a cam with 248@ .050 duration and it will idle at 12 degrees initial. Not very well but it does run. Are you saying even with 28 degrees initial it will still not idle in gear? Are you running a real tight converter?
For a 383 motor that is not a huge amount of duration. It should run and idle in gear with that setup with the vacuum advance in at idle.
For a 383 motor that is not a huge amount of duration. It should run and idle in gear with that setup with the vacuum advance in at idle.
I suspect it is the stock converter which is part of the problem but it should be able to idle.
With the vacuum advance hooked up, it idles fine in park. But put it in gear and it stumbles and dies. I get about a 275-350 rpm drop when I put it in gear.
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 990
Likes: 0
From: North Texas
Originally Posted by Techno
Why not retard static by 4* and adjust the idle screw so it don't stall out?
You didn't say what it does idle at though.
You didn't say what it does idle at though.
Currently, I have the idle in netural set to about 950 which seems high.
I need to keep the idle at about 750-800 to keep it running.
Drifting
Joined: Nov 2001
Posts: 1,469
Likes: 6
From: 68 427 4.11s Roadster
If your engine is high duration then it ain't going to idle down low, its the nature of the beast.
If your engine is new then wait until it breaks in then the idle will be more adjustable.
If your engine is so finnicky with 4* then something else is the cause. 8* should be fine. it should also idle just as good at 950 with 12* as it does at 950 at 8*.
None of these numbers are set in concrete -good for every engine combo there is.
Should check what vac advance adds to the timing picture also. Mine turned out to be too much.
If your engine is new then wait until it breaks in then the idle will be more adjustable.
If your engine is so finnicky with 4* then something else is the cause. 8* should be fine. it should also idle just as good at 950 with 12* as it does at 950 at 8*.
None of these numbers are set in concrete -good for every engine combo there is.
Should check what vac advance adds to the timing picture also. Mine turned out to be too much.
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 990
Likes: 0
From: North Texas
Originally Posted by Techno
If your engine is high duration then it ain't going to idle down low, its the nature of the beast.
If your engine is new then wait until it breaks in then the idle will be more adjustable.
If your engine is so finnicky with 4* then something else is the cause. 8* should be fine. it should also idle just as good at 950 with 12* as it does at 950 at 8*.
None of these numbers are set in concrete -good for every engine combo there is.
Should check what vac advance adds to the timing picture also. Mine turned out to be too much.
If your engine is new then wait until it breaks in then the idle will be more adjustable.
If your engine is so finnicky with 4* then something else is the cause. 8* should be fine. it should also idle just as good at 950 with 12* as it does at 950 at 8*.
None of these numbers are set in concrete -good for every engine combo there is.
Should check what vac advance adds to the timing picture also. Mine turned out to be too much.
Ok, I will look at it again just to verify.
Yes, the new engine only has 200-300 miles on it so far which goes along with your information.
