Hi,
I have installed a old MP race ditributor part 4120942, think its from the early seventies. It have tach drive.

It seems to be looked, its have no mechanical advance. I have a new MP billet race distributor on my other car and that one you could adjust the mechanical advance with changing the slots (bigger or smaller) and lock it with a screw.

Havent disassembled the old race distributor yet but do anyone know how to adjust the mechanical advance, is it the same as the new billet race distributors (mopar performance)? Just change the size of the slots. I think its a kit for the right size, advance curve kit...

Thanks folks,

I don't know how to lock it , maybe be as easy as tightening a screw that I believe is under the rotor , but those old mopar race units are not adjustable like the current MP electronics distributor ...

I'll refer to Rapid Robert on how to adjust the mechanical advance on the old units , involves welding and filing , I'm sure he has his procedure on a clipboard on his computer for a quickie copy and paste because it posts it up a few times per week ...

The new MP billet race dist have the same advance curve system as the mallory unit. Same way to adjust the mechanical advance.

Okay, I will search here again to see if Rapid Robert have post some about change the advance in the old race distributors.

The engine is dynoed with another dist. The egine want initial 15 degrees and total of 33 degrees. With this old MP dist I could choose of 15 or 33

Was surprised it even started with 33 initial. Must be the street compression... The old dist dont advance the ignition... Want initial 15 and advanced to total 33

Please help, the mechanical tach and the old gear drive distributor really does it!!

Its the aluminum one, part no 4120942.

It may have the same thing done to it, if you hold the bottom distributor shaft and try to twist the rotor and it has no movement either way it is probally locked in (welded advance)to the bottom shaft

I only have one spring for the mechanical advance, the other was missing. It wasent locked or welded. The Slots in the advance plate is modyfied and measure 0.470 inch. I think its about 18 degrees mechanical advance.

Is it any spring kit for these distributors?

So, if it has a slot, and is not welded, why is it locked then? I really cannot see the problem?

Here's some info. EDIT The mr gasket light spring kit is 925B iirc. The MP kit is P2932675. the crane kit (which is no longer available new) had a plain spring a yellow spring & an orange spring & they recommended to always keep the OE light spring & sub in something instead for the heavy spring with the long loop on one end.

Thanks but what do point x and point y means and singel and double spring. I have one spring installed right now, that gave my full advance directly. Its that a singel spring set up or what do singel spring means...

I will look in my msd distributor (which the engine was dynoed with) which parameters I will look at but I think I need full mechanical advance 18 degrees and kick in fully at about 2500 rpm.
What springs do I need?

Also the slots measured 0.470" have seen a table here that stated 15 degrees x 2 for that slot size, correct?

I want 18 degrees advance, should I aim for 0.390" slot size (advance plate). In a mopar muscle magazine article I read 0.370" was 20 degrees in advance plate.

Point X is when the advance starts and point Y is when the advance is maxed out. Single/double means (1) spring or (2) springs of the OE light springs that come (1) to a dist. Reportedly the slot length/adv amount chart ain't dead on so file em slightly less than the chart because if you go too far it means another trip to the welder & yes you will have to be in & out of there several times till you get it dead on. I would find the initial your eng wants with the "vac gauge method" then shorten the slots to get 35 (SB) or 36-38(BB) total (both initial and total set with vac adv capped) then work with the springs then plug in/adj the vac adv. EDIT I see that race unit has no vac adv so that's 1 less subsystem to tune. After setting initial and total I'd mix/match springs till you get just under the pinging point at WOT up thru the gears on your hottest/driest (most likely to ping) day no matter what RPM that makes the slots max out at. You want the curve to start (point x) several hundred RPM above your idle speed in drive

Thanks! Did they come new with only one spring installed? shouldnt both weight have a spring (stock setup).

Yes, for the moment I only have one spring and installed the distributor on 15 initial pointing at # 1 terminal at distributor. What happened was that the total timing was still 15 degrees.

Turn the distributor to initial 33 which I want the total to be. The total was 33. It dont advance the mechanical or more correct, it go total mechanical direct.

I will buy a springs and install one spring to each weight (two springs). I hope it then not directly go the maximum mechanical total advance.

Hope you guys understand me, I'm swedish

Are you able to move the rotor back and forth by hand if you hold the shaft that keys into the oil pump drive ? If so then it's doing what it is supposed to do with 1 light spring and those 2 weights ... go right to max advance at idle.

That distributor is called a RACE distributor for a reason. If you want it to act like a street distributor then you'll need to put in springs similar to a street distributor.

Yes I can, the mechanical advance work and I understand the total kicks in directly. I will put in one more spring and test and tune. I drive it to the races and want it to cruise in some way, even if it spit and roar.

Thanks fellows!

Will pick up a new spring kit tomorrow. Dont know what brand but as I was told they are for recurve the mopar distributors.

On dyno the engine worked out best with initial 15 and total 33 degrees. That it was I aim for...

Thanks again!