I have read numerous posts on how to do it but now its time so I would like a little help. Its is a 10/15r with 15 being the used side. Currently it has 8* initial and a max of 21* @ 2300 nothing beyond that. I have taken the distributor apart and cleaned it all up had a look at the springs. As many others it has a small and large one with the larger not preloaded. Vacuum was plugged while checking. My real question is can i grind the 15r side where it stops the mech adv nad gain more adv?? How much mech adv is too much?? Any ideas how much to grind to start with? Don't mind experimenting on it even if the end is a &$*(£€ distributor, its about learning a few things along the way. Right now it runs god but i know it has some more potential in there and i would like to harness it.
I have the tools, timing light with tach, vac guage, vac pump and infinite time.....well dont tell my wife i said that.
Once the mech adv is as good as its going to get ill tackle the vacuum adv......
Thanks Matt, I read your post when you did yours. I will plot my curve later and maybe get some input. I did grind about 1mm out of the notch and it bumped up the total adv to 23. Look forward to learning as I go.
Did you use a vacuum pump to find out what the vacuum is going to add to your total?
Did you hook up a vacuum gauge to the engine and drive steady throttle at about 55 MPH to know what your PTC (Part Throttle Cruise) vacuum signal is?
Without mapping the vacuum curve with a vacuum pump,
Noting how much advance each In.Hg. Vacuum pulls in,
You can't tell what your total will be by just jacking with the centrifugal...
Adding weaker springs brings in centrifugal advance faster,
And that adds 'Zip' or makes the engine feel like its pulling harder at lower RPM through mid range RPM.
You *Usually* don't have to add a lot of centrifugal advance if you have 15 to 18 degrees,
You just use springs to bring that advance in 'Faster' (lower RPM).
The size of the spring is a thumbnail,
Its TOTAL spring pressure that allows faster or slower advance.
Now, consider your 'Take Off The Line' power,
Let the clutch out at idle, when you get rolling, NO Throttle,
Then stomp on the throttle, let the engine rev to about 3,000 RPM.
Since when you stomp the throttle, you DUMP any vacuum,
Vacuum advance is NOT in play here,
This is carb tuning and centrifugal timing working with your Tire size/Gear Ratio.
If it bogs down a split second, then takes off,
You have an Accelrator Pump TIMING issue, the pump shot is coming in a split second too slow.
If it JUMPS, then bogs down, then takes off slower/less pull than you think it had when it jumped,
Then your pump shot isn't large enough or its not long enough.
Can be a pre-loaded pump not getting full,
Could be a weak stream,
Could be a leaking piston,
Could be a linkage adjustment.
If the vehicle doesn't bog, continues to pull EVENLY,
Then its time to experiment with springs...
Working DOWN in total spring tension...
When changing to weaker springs adds nothing to the pull of the vehicle,
Then you have reached the maximum the engine can pull,
Back up the springs to the point where it stopped pulling harder, and use those springs.
The reason for the slightly heavier spring pressure is,
You are getting ready to tune vacuum advance, you have maximum pull,
So you are wasting vacuum advance control...
Vacuum advance is your economy while driving...
Wasting that advance control now is going to hurt you when you try to tune out 'Pings' & 'Knocks' while under load and at part throttle.
You will be right on the ragged edge of detonation, you will need the adjustment to get the vehicle running correctly on the highway at PTC.
Thanks for jumping in jeephammer. I know you have been over this a few times in several posts. I have not plotted my vacuum but will tomorrow as well.as the cruising vacuum. Once I have these numbers ill post up both the centrifical and vacuum and i hope you can make a few suggestions from there. I was under the impression to get the centrifical dialed in then work on vacuum. I stand corrected and will do.as you suggest. As far as stomping it (3 speed auto) it pulls nice and evenly no bogging anywhere unless its just warming up then i have a little at about 1/3 - 1/2 throttle but it goes away quickly once its warmed up. I think the manifold heater isnt working (on my list). Think it might be the relay.
With just the small amount of tweaking i did yesterday it ran and idled better then ever. Not that it ran bad but better with more power by my butt o meter. It actually spun the tires in gravel. 2.73 gears with 31's (gears are on my list 4.10 with 32-33's).
Thanks for taking your time to help out a fellow jeep enthusiast.
You are doing it correctly. Get the centrifugal dialed in, first, then check the vacuum advance.
Your engine will never see the total of all three advances (initial, centrifugal, and vacuum) in any loaded situation. At WOT, the vac advance isn't even in play because there's no vacuum. At partial throttle cruise, your engine will be seeing only a portion of the centrifugal (depending on RPM) and only a portion of the vacuum (depending on load).
As Hammer said, the vacuum advance adjustment doesn't affect how much advance it adds, only how quickly it kicks in. If your vac canister is like mine, it will add a max of about 15-18* at the highest vacuum levels. I like Shawn's recommendation to have all the vac advance in at around 2" below your idle vacuum. So, if your idle vac is 18", set the vac advance to be all in at 16". That should give you the right amount of advance at PTC and other light load situations.
So my vacuum adv is stripped so went to the local parts store and a whole new distributor is the same price as just the vacuum adv. Before i buy it i want to make sure im going the right route. Its pretty cheap at 70 bucks. No details on it as to whats inside it though.