Distributor curve

[CamaroAdam73]

Alright i made some progress with the car, i still don't have a better timing light so there's only so much i can do right now.

I switched to the lightest set of springs for the curve, then set initial timing to 19 degrees. Runs like a champ, doesn't stumble or stall at all and holds steady idle in gear.
The vacuum advance is coming in at idle 12" of vacuum, i don't know if its supplying the full 15 degrees though.


Still trying to figure out why the primary pull off won't release.

 

[Fox80]

If I understand you' sounds like you are getting there, so you are saying your motor makes 12" of vacuum at idle at the manifold?? If that is the case then you might want to change the vacuum canister to one that requires less vacuum than that to achieve full open. Is the vacuum the motor produces at idle stable? Or does it make the gauge bounce at bit, say from 12" -14" as the motor lopes? A motor that makes wandering vacuum at idle should have a canister the requires less than the low end of the vacuum the motor produces so that the advance doesn't wander around at idle. Some people will also use an adjustable canister, I have never used one of these but motor places around me are starting to use these a lot as guys are no longer wanting that lumpy cam sound in a motor, they just want the motor to run its best. These adjustable canisters still require 15' of vacuum but what is adjustable is the amount of advance the canister will apply. I've been reading up a lot on these lately to try on my car, this would allow you to lessen up the mechanical advance so say it would swing from 10-20 degrees off the springs, you could then set your mech. base timing at say 22 and limit the vacuum pull to only ad 8 degrees more or something like that. Do some google searches I have found hundreds of good articles on this subject, I try to avoid the forums that talk about this stuff and just concentrate on the tech-type articles. But for sure try and find yourself a dial timing light, the "drive and ping" method is hard on a motor.

 

[CamaroAdam73]

Yes 12" of vacuum at idle from a manifold source. yes the vacuum reading bounces around alittle bit, variations where small i didn't take note. The vacuum advance i have is an adjustable one, i thought the adjustable part was adjusting when it came in. I'll pickup another one that comes in at a lower vac signal.

 

[Fox80]

It's sounds like the erratic idle timing is from the lack of vacuum the motor is producing, if you are making a wandering 12" of vacuum at idle that is not enough to deploy a standard canister so you get the pull and release of the advance rod. I would start with the Elgin #VC1810 also sold as AC Delco #D1312C I have heard that napa no longer carries the Elgin part, I haven't had to buy one in years because I have some laying around so I don't know for sure. I believe Autzone sells them under a similar number. Either way the can you are looking for will be stamped "B28" all canisters are made by one company so the stamping should be on there. I believe a "B20" is a stock type can and the "B1" is the very low vacuum can. The adjustable canister ONLY adjust the max amount of advance the canister will allow it to pull NOT the amount of vacuum required to pull it. Good luck

 

[pontiacgp]

Yes 12" of vacuum at idle from a manifold source. yes the vacuum reading bounces around alittle bit, variations where small i didn't take note. The vacuum advance i have is an adjustable one, i thought the adjustable part was adjusting when it came in. I'll pickup another one that comes in at a lower vac signal.

Why not try the vacuum from a ported source, the vacuum won't have any effect until you hit the gas so it won't be affecting your idle. That's the way GM had it set up

 

[Fox80]

Using a ported vacuum source to hide the problem with an incorrect canister is not the correct way to do it, the motor will still have wandering timing at cruising rpms, that could cause "pinging" or a stumble on acceleration. The reason gm used ported vacuum was to not allow the vacuum advance to work at idle in an attempt to cut tail pipe emissions

 

[pontiacgp]

there is alot of online discussion with obvious seasoned guys about ported or manifold vacuum for the hei and some use ported and some use manifold so I don't see any harm in trying it both ways and he can see what way he likes

 

[Fox80]

I'm not disagreeing with the fact that you can use ported vacuum to not allow it to advance at idle, I am disagreeing with using it when you know that the motor doesn't produce enough vacuum to pull the canister the way it is supposed to. The problem of wandering advance because of low vacuum will not go away with a ported source. That is the reason to at least try to use manifold vacuum, to see exactly what the dist is doing at full, plate closed, vacuum it is impossible to know this while driving it when the car is at cruise rpm.

 

[pontiacgp]

the reason why I'm suggesting to try it ported is if the manifold vacuum at idle is causing issues once past idle the vacuum increases and the vacuum advance should not fluctuate. It's a game of trial and errors without being able to analyse the air fuel ratio and with no dyno. The MSD E curve is one distributor that takes out some of the guesswork though, you set a centrifugal advance and vacuum advance curve electronically.

 

[CamaroAdam73]

I looked into the MSD E-Curve but couldn't find one for an oldsmobile, would have been nice though.

Right now I've got everything setup to use a manifold source of vacuum, based on how the engine runs i think with a ported source in gear the car would stall allot. When setting initial timing..ext with the vacuum advance disconnected it runs rougher. I can't see what the timing is doing with the vacuum adv connected but i think it is fluctuating, i'm picking up another vac adv today from napa, comes in quicker. Too bad they don't have one that comes in quicker / can adjust.




I have seen people with aftermarket setups, setup to run on ported vacuum and they ran pretty strong..