Some notes that may be helpful to other Mallory YH (Mopar Performance) distributor owners....
I used Mallory's kit to tune my distributor, Mallory PN29014:
As noted by ryanwblandon
, my MP unit was setup with two pink springs which gets you a single stage 'matched spring' advance. Mallory's notes in the kit say that any YH unit PN that ends in -05 will have two pink springs. The mechanical stops were full open which provided 32º total mechanical advance. I started with a 28º total @2200rpm/2ºATDC @750rpm initial.
I installed Mallory's recommendation for springs: Purple/brown. The purple spring is loose on one end which gives the curve a 'two-stage' effect. I adjusted the mechanical stops using the 20º tab from the kit. MP setup info lists 32º for my heads ('69 X). I was after something in the vicinity of 12ºBTDC initial with the listed 32º mechanical total.
The stop tabs on the YH advance mechanism are iffy. The plate is sloppy, making it easy to end up with the two stops at different settings. The differently marked tabs are less than stellar when it comes to setting the stops. Even with making sure the stop-tab plate is 'equal' on both sides, the 20º tab fit differently from one side to the other. A bit of 'tweak' to the tabs will take care of that. DO
take some care when setting the mechanical stops if you want both of 'em the same.
The end result was a 33º total @3100rpm, a 12º initial @900RPM. Just a tad 'off', but something expected considering how loose the stop mechanism is designed.
The vacuum can on my MP distributor is stamped '11R'. With vacuum attached, I had 52º @3300rpm.
I did notice the timing tape appeared to be considerably more steady AFTER the spring replacement.
I've read BOTH
descriptions of what CW and CCW accomplishes, but on my MP distributor a CW adjustment resulted in a later/slower vacuum advance, a CCW adjustment was sooner/faster. The total advance didn't change, just WHEN it started and how FAST it completed. If you want a different
amount of advance, you will need a different vac can.
The plate assy was a tight fit in the distributor body. It had to be pried out. That made reassembly a pain when fussing with the vacuum can tab. A bit of look-see will likely show where the plates are binding on the body. In my case, where the screw tab was bent on the plate had a couple rough spots. A touch of a file (keep any filings off the pickup!) to those spots made the fit a LOT easier.
My idle is much better. It will still hang when the engine is hot..but not to the extent it did prior. A 12ºBTDC sure helped the brake booster! I used to 'run out' of power brakes on a regular basis. Yeah...I have a vacuum 'storage' can, but it happens to be sitting in a 'spare parts' box..NOT on the car. A whole lott'a good THAT does, 'eh?
The car runs considerably better. Part of that surely due to adjusting the 4-corner idle mixture screws. A completely non-scientific nor mathmatically correct fuel consumption 'test' (looking at the fuel gauge) showed a considerable increase in fuel efficiency. Engine runs hotter, starts a tad harder. By 'harder' I mean it used to fire with just a t-o-u-c-h of the starter, now it cranks a revolution or two. Not a big deal.
IF you are running an MP distributor, don't hesitate to get it tuned. I should have done it LONG ago. Simply didn't get it done.
A btw..but with a carb sync tool connected to the manifold/port nipples on my Holley the difference measured between the two isn't much..a couple of inches off-idle is all.