I am having a hell of a time trying to tune my vacuume advance can on my distributer. I just got my distributer brand new on thursday from don at FBO systems. Its a mopar performance distributer. I am running my vacuume advance off of ported vacuume, altho don told me i needed to run it off of manifold vaccume, i tried the manifold vacuume and just couldnt get it to run good. mainly idle...
I have my initial timing at 16 degrees and my total timing at 34 on a 300 hp crate 360 magnum. I have never tried to tune a vacuume advance can so i dont even know if turning the adjustment screw insie the vacuume can clockwise increases it or decreases it. In my mopar engines book it says i need 52 degrees total timing including the vacuume advance, but i have been told that with todays fuel 45 to 48 is better.
Somone please explain to me step by step what i have to do to get my vacuume advance tuned right. I know it is off because at light cruising speeds it is cutting in and out and and running crummy. but at half or wide open throttle it is great.
Do i hook the vacuume advance up and get my timing light out and just keep adjusting the adjustment screw in the vacuue can untill i'm reading 50 degrees total with the vacuume advance?

Turning the screw does not increase or decrease the amount of advance.. All it does it adjust when the advance comes in..

Does it run well with the vacuum advance disconnected? If not, get that figured out first, and then and only then work on the advance.

And like shorty said, adjusting the screw only changes how much vacuum causes it engage. You'd have to take the cap off and find a way to limit/lengthen the travel to change how much advance it provides.

Ideally this is done with something like a mity-vac so you can apply measured vacuum at idle and see the 'curve', then adjust it accordingly.

I know for a fact that it is the vacuume advance causing my probelms.
so does turning the adjusting screw clockwise decrease the amount of vacuume or increase it? Thats is what i need to know the most. Because i will just turn it all the way down and turn it out 1 turn at a time untill it starts running crummy at cruising speeds then i will back it off. Thats the only way i see myself getting it close to right because i do not have a mighty vac or a vacuume gauge.

There should of been instructions with the dist. If not call FBO to find out why not..
Your best bet would be to take it to a dist shop and have them set it up.

hmmm. dropped my fbo dist in, set it to where the sheet said and it ran great. i would call FBO before you mess around and screw with the dist.

Yes I would give Don a call 1st. Vac adv changes rotor phasing so you might check that too. Drill a 1/2" hole in the top flat of the cap 2/3 of the way between the center terminal and the terminal with the #1 plug wire on it & shine your timing light straight down onto the rotor blade at the offending rpm & see if it is pointed at or very close to the cap terminal. Can use a Mityvac to pull the can thru its' travel EDIT use a 3/32" allen wrench turning it 2 turns CCW at a time to reduce when the curve starts then take it out & try it & see if that helps

""hmmm. dropped my fbo dist in, set it to where the sheet said and it ran great. i would call FBO before you mess around and screw with the dist.""

Me two.

Since Don now sets up his distributors for manifold vacuum, you should probably go back to that or call Don. But I will give you some friendly advice before calling Don. As soon as you tell him that you are not hooking it up to manifold vacuum, he will be curious why.

I did have to richen up my idle mixture once I got the distributor in and set correctly. With the extra timing at idle when the VA is hooked up to manifold vacuum, you may need to richen up your idle mixture to compensate for the extra timing.

Note: Don said that this setup (manifold vacuum) requires 12" vacuum minimum (auto or manual) to keep the can happy. Once I had mine setup, my IN DRIVE (with brake applied) came out to right at 12"hg but the idle was too high. So I lowered the in D idle rpms down and I am now getting 11-1/2" hg minimum and the idle is still steady. I definitely would not try to run this distributor with less than this for a vacuum reading. I would guess that I am on the ragged edge of keeping the can happy.

Pretty simple get it running as good as you can with vacuum disconnected and plugged. get total where you want it and if it has enough idle advance to idle well in gear leave it and drive it a while. if it needs more idle advance work the curve till it does.

Then after driving and your happy plug vacuum advance into ported vacuum and drive if it pings put a 3/32 allan wrench in through port and turn counter clockwise maybe 3 turns to start and drive then keep adjusting this way 1 turn at a time till any ping at light cruise is gone!

So turning the adjustment screw inside the vacuume advance vcan counter clockwise reduces the amount of vacuume needed to engadge the vaccume advance and turning it clock wise increases the amount of vacuume needed to engadsdge it? or is it the other way around? that is all i need to know at the moment.

other way around

So if i'm getting too much vacuume advance i need to turn the adjustment screw counter clockwise correct?

too much too fast-turn it CCW. At max vac you'll still have the same amt (total) but until then CCW will slow the onset

ok, so i called don at fbo and he told me that with the vacuume advance plugged into full time manifold vacuume i should grab my dial back timing light and that it should read 30 degrees while at an idle.
!6 degrees initial and another 14 degrees with the vacuume advance this is on a 300 hp crate 360 magnum. So i checked it and it was sitting at 24 degrees whie at an idle, so i turned the adjustment screw inside the can one turn t a time and kept checking it and the total was not rising. So i decided to goose the throttle real quick to see if maybe the vacuume can arm was sticking or something and sure enough after goosing the gas real quick the reading was at 27 degrees at an idle.
So i jumped back in under the hood and turned the screw in almost another full turn clockwise and checked it and it was sitting right at 29-30 degrees while at an idle and it was popping out the exhuast a little bit so i turned my idle air mixture screws out a half a turn each and that took it away. I took it for a drive and it seemed to be doing pretty good.
Does this sound right to you guys? 16 degrees initial 14 in the vacuume can and 34 total all in by 3000 rpm. On a 300 hp crate 360 magnum in a half ton short bed four wheel drive? If i'm reading 30 degrees at an idle with the vacuume advance plugged into full manifold vacuume then i must be sitting right at where don at fbo systems said it needs to be. He siad he has tuned and helped tune alot of these crate 360 magnums and that this is what the majority of them like.

so what do you think rapid robert? does it sound like i have it nailed down right now?

No, do not get the desired total initial timing with vacuum advance by adjusting the advance can. Disconnect the vacuum advance and plug the port on the carburetor.

Now set your initial timing at 16 degrees.

THEN plug the vacuum advance in. It really doesn't matter exactly what the vacuum advance does for full throttle performance, but set it up how FBO advised. If it isn't 30 degrees once the vacuum advance is hooked up (to manifold vacuum) then adjust the vacuum advance can accordingly.

Your timing is probably a few degrees retarded of the recommendation from FBO.

Don't forget that idle speed and the timing will both effect vacuum at idle, and thus will effect how strongly the vacuum advance can be pulled. Make sure that the car is up to running temperature and that the idle speed is set where you want it with the advance hooked up to check your initial timing with the vacuum advance before you fiddle with the adjustment in the vacuum advance can.


EDIT: I may be misunderstanding what you did, but confirm that you set it up the way that I recommended.

""If i'm reading 30 degrees at an idle with the vacuume advance plugged into full manifold vacuume then i must be sitting right at where don at fbo systems said it needs to be. ""

It sounds like you have installed it correctly.

Now you just need to tune your metering screws for the best vacuum reading in N (for manual tranny ), or best vacuum reading in D with brake applied (auto) and then take note of your vacuum reading to make sure that it is above the 11.5-12" reading. If so, then you are good.
Note: The engine needs to be at full operating temp "before" this final tuning process.

yo7_a66 you were dead on right about the idle air mixture screws needing to be adjusted. I called don at fbo he told me to turn them out a half turn each. I have the edelbrock performer 600cfm manual choke carburetor. I turned them out a half turn each and it fixed it.
And i set my initial timing to 16 degrees with the vacuume advance plugged off. then i put it on full manifold vacuume and then i adjusted the vacuume can untill i read 30 degrees at an idle with the vacuume advance hose plugged to full time manifold vacuume. So i think i have it set up the way don wants it to be.
I'm going to call him to find out for sure tho.

yes, i called don and he confirmed that this is where my timing needs to be. So now that i have ignition squared away i can work on adjusting the carburetor.
I think my set up may benefit from a richer accelerator pump shot. I'm going to give that a try and see what happens. I'm running the 7042 edelbrock metering rods and the silver step up springs. And my jets are the .092's front and back. I eventually want to get a different carburetor, this edelbrock has not really impressed me, there isnt enough adjustability on them.