No vacuum advance. 16 initial 36 total. I have been through this in several threads. The factory older distributors are fixed timing advance. the newer distributors are adjustable. On the fixed older distributors there are two way to go. Either way you want 20 degrees total no more. You can never achieve that without closing the slots with weld or having an adjustable slot in a new one.
When you are checking for total it is exactly what it defines Total. Not what it is at a certain RPM. Total is Total amount of travel and should be in at. At least but not before 2500 rpm's
Another words if you total is 36 at 2500 it should not keep going up with RPM's. The reason for your total being in at that RPM is so you do not exceed over 36 over that RPM. Once you have your total which should be set first. Let it come to idle It should not go less than 16. If your motor likes a total of 35 initial should be 15. So 20 degrees is the number of travel you are looking for. This can be confirmed by MSD built in initial on their digital systems. It is 20 degrees. That's the number that works in all applications without failure. example 38-18, 37-17, 36-16, 35-15, 34-14 and so on.
The reason the slots are so large on a stock distributor the mechanical advance has a large slotted stop spring used in conjunction with the vacuum advance. This is used for fuel economy. When no throttle is applied at cruising speeds the timing is controlled by both giving the motor and easer free running combustion so the firing doesn't try and force the piston down before it reaches the top. Or to late that it loses the compression for power out of the atomization of the fuel.
So if you have change the camshaft in your motor. You are changing the over lap of the valves in relation to one another. This reflects on the cylinder pressure for combustion and the vacuum signal used for the factory advance. I know the advance is adjustable through the vacuum port with an allen screw. But unless you have a distributor machine or get lucky you shouldn't even play with it .
All factory distributors have different vacuum advances. you will see the vacuum apply inches stamped on the arm of the advance. 318 2bbl is 11.0, 340 4bbl is 8.5. all early performance distributors from DC, or mopar perf. are 8.5 . these are to be used with factory spec motors or Mopar cams with the correct calibrated comp.
I will try and tell you how to correct this problem your having if it is Dist related. If it is retarded to far at initial it will not start easy.
The slots in the distributor should be welded up or you can just do one they work together. If you weld up one it will stop both. They are 1/2 inch weld them to 3/8 this will give you 20 total from what ever initial. Initial is first when the distributor is not spinning and the it achieves total when spinning. But when setting a distributor you want to set total first not initial. Total is more important. If this is not correct it will cause damage to the motor. Never and I mean never should the total be over 38 and that is with premium fuel.
When welding the distributor slot you can weld the outside or the inside depending what springs you are going to use and how fast you want your total in. this is determined by cranking pressure do to cam , piston choice and fuel.
For example I have a very large cam in my motor so I do not have much Idle pressure so my distributor is locked. But I have a MSD with a built in retard feature. My timing is set at 35 that is my total and also my initial at idle is 35. But when I shut my car off it automatically retards 20 and goes to 15 when I am restarting the motor. The box keeps it ay 15 until it starts and then lets go at 800 RPM's allowing My initial at idle and my total to be locked at 35. But for starting the motor it is at 15.
Now back to the slots . When I weld up the slots I weld up the inside If I am using the two light springs from mopar. This puts tension on the springs and stops the motor from going in and out of total at idle. If you ever here a motor going up and down at an idle constantly this is the cause . Timing going in and out because of timing springs to light. A lot of guys that just install light springs have this problem . Some guys especially with blowers think this is cool.. Total usually comes in at 2000 this way. weld the outside its in at about 12-15. My usual method for a customers dist, Is weld up the outside and use one light mopar spring and leave the medium spring in This allows total to be in at around 2500 and if your motor wants a quicker total you can just take out the light spring.
1. remove vacuum hose
2. Set your total. Never more than 38 degrees. and should be done at 2500 take it higher if it moves springs are to heavy
3. check your initial It should drop 20 under total at Idle. if more slots to large
4 If you like fuel economy over performance hook the vacuum up.
or if you like the hose you bought being hooked up so it looks Nice plug the hose with something .
Hope I didn't miss anything . .I know there will be guys with their own opinions and won't agree because this isn't how their car is. and theirs is just perfect. I am going on 57 and have been doing these since just after birth . On my cars you can reach in tap the key and its off and running . If it cranks once your lucky. Sound like an electric motor up in RPM's. Good luck and hope you enjoyed the book..
I highly modified and installed a VW Beatle pro-comp Distributor. Just so I could use a Boost Master, MSD 6al , Methanol inj., and Blower on a 2.2 Omni,
I believe I have a Mopar distributor from my Duster here. It has a lean burn plate and vacuum block plate and is adjustable . It is set up for 20 at 2500 if anyone is interested. I went to a roller bearing MSD for extreme RPM's . Steve
