Distributor Spring Question
Thread Starter
Racer
Joined: May 2007
Posts: 357
Likes: 28
From: Northern AL
The
Le Mans Master
Joined: Mar 1999
Posts: 5,403
Likes: 989
From: Itasca IL
You'll have to experiment to see if it will run OK with the vacuum now. Even if the bucking/surging goes away, you still may have some part throttle spark knock under conditions where the mechanical advance is coming in and manifold vacuum is still high enough to be adding vacuum advance (i.e., between about 2200-3000R).
Nick
Thread Starter
Racer
Joined: May 2007
Posts: 357
Likes: 28
From: Northern AL
26* is about right on with the initial set at 10*. I don't know which can is most correct for your application. However, if you have 40* idle, something is amiss with the mechanical advance mechanism. You will need to start with the gold springs, as I am absolutely sure that will prevent any mechanical advance below 1200R. Then you can ascertain how much base timing you have and how much advance the vacuum canister is adding.
If all seems normal after doing the above, then disconnect and plug the line to the vac and use a dialback light to see how much mechanical advance you're getting and how fast it comes in. I know others will disagree here, but in my opinion even the stiff springs will allow the vacuum advance to come in too soon for use with pump gas. You can experiment with cutting coils out of the gold Accel/ Mr Gasket springs to elevate the curve in the RPM range, or better yet find some OE springs from an old distributor that are made from larger wire diameter and therefore have a higher spring rate.
If all seems normal after doing the above, then disconnect and plug the line to the vac and use a dialback light to see how much mechanical advance you're getting and how fast it comes in. I know others will disagree here, but in my opinion even the stiff springs will allow the vacuum advance to come in too soon for use with pump gas. You can experiment with cutting coils out of the gold Accel/ Mr Gasket springs to elevate the curve in the RPM range, or better yet find some OE springs from an old distributor that are made from larger wire diameter and therefore have a higher spring rate.
With the gold springs, my initial timing is 10* at 800 RPM. Without any VA, at 2400 RPM the advancement is approximately 26-28* using a dialback. So total 36-38 without vacuum at 2400RPM.
Thread Starter
Racer
Joined: May 2007
Posts: 357
Likes: 28
From: Northern AL
Jim,
You'll have to experiment to see if it will run OK with the vacuum now. Even if the bucking/surging goes away, you still may have some part throttle spark knock under conditions where the mechanical advance is coming in and manifold vacuum is still high enough to be adding vacuum advance (i.e., between about 2200-3000R).
Nick
You'll have to experiment to see if it will run OK with the vacuum now. Even if the bucking/surging goes away, you still may have some part throttle spark knock under conditions where the mechanical advance is coming in and manifold vacuum is still high enough to be adding vacuum advance (i.e., between about 2200-3000R).
Nick
jim
Team Owner
Joined: Aug 2007
Posts: 58,061
Likes: 7,147
Army
That sounds pretty good...with the vacuum advance and the timing 'all in' at speed you don't want over 50* ... prob 48* would be best.... Looks like you've zeroed in on the problem...
My little 283 is 'all in' at about 2900 RPM and that has given me good response throughout my typical driving range...
My little 283 is 'all in' at about 2900 RPM and that has given me good response throughout my typical driving range...
Melting Slicks
Joined: Jul 2004
Posts: 2,871
Likes: 196
From: Maryland
I still think you'll have to recurve the distributor to a less aggressive map.
My 300 hp distributor mech advance map
Start @ 800 rpm
14* @ 1600
26* @ 3100 rpm
Using 10* initial timing yields 36* total timing @3100 rpm. Im using HD Borg Warner 112 Hp points, Accel rotor & cap that are USA made and a B22 VAC . I can idle smoothly @ 600 rpm and my cruise timing (part throttle) is 51*.
My 300 hp distributor mech advance map
Start @ 800 rpm
14* @ 1600
26* @ 3100 rpm
Using 10* initial timing yields 36* total timing @3100 rpm. Im using HD Borg Warner 112 Hp points, Accel rotor & cap that are USA made and a B22 VAC . I can idle smoothly @ 600 rpm and my cruise timing (part throttle) is 51*.
Last edited by Donald #31176; Apr 18, 2010 at 11:53 AM.
Thread Starter
Racer
Joined: May 2007
Posts: 357
Likes: 28
From: Northern AL
I still think you'll have to recurve the distributor to a less aggressive map.
My 300 hp distributor mech advance map
Start @ 800 rpm
14* @ 1600
26* @ 3100 rpm
Using 10* initial timing yields 36* total timing @3100 rpm. Im using HD Borg Warner 112 Hp points, Accel rotor & cap that are USA made and a B22 VAC . I can idle smoothly @ 600 rpm and my cruise timing (part throttle) is 51*.
My 300 hp distributor mech advance map
Start @ 800 rpm
14* @ 1600
26* @ 3100 rpm
Using 10* initial timing yields 36* total timing @3100 rpm. Im using HD Borg Warner 112 Hp points, Accel rotor & cap that are USA made and a B22 VAC . I can idle smoothly @ 600 rpm and my cruise timing (part throttle) is 51*.
I'm so happy to get her running good again but will re evaluate. I had an Accel universal VAC that is throwing 30* advance at idle. I have it plugged right now but will replace with either a B22 or a B1 VAC.
I have the top end and the bottom end of the curve mapped but I didn't take any measurements in the middle. In addition, I may experiment with a couple different spring combos. This was a first for me (points, gaps, dwell, springs, etc...) so know that I have a better feeling on how all of these interact with each other I can regroup and get a good setup.
Good news is though she runs better than she has ever!
I appreciate your feedback.
Jim
