Go Ravens

Got my trusty old dwell meter out and I can only set the dwell to about 25 before the motor dies. Since 30 is recommended, why would this be? Worn distributor cam lobes?

Smokehouse69

Steve,
Are you sure that your Dwell tach is set for 8 cylinder and not 6 or 4?
On my dwell tach there are two settings a 6 and 8 cylinder setting, for a 4 cylinder you divide the dwell reading by 2 (I think, maybe you multiply by 2, I can't remember which.)
Check you meter.

Go Ravens

Nope, set for 8.

nunus79

Its been a long time since I've messed with points. I seem to remember that when you adjust the dwell the timing is moved also. Maybe your timing is becoming too retarded.

Z-man

You can visually check the cam lobes. Do they look destroyed? Most distributer cam followers are fiber and won't wear the lobes to any extent.
Have you checked the gap? Specs for '70 are .016 new - .019" used, with dwell 29 - 31 deg. I usually set the gap, fire up the car then set the dwell to within range. Then I set timing by starting from a retard position until pinging point, then back off until pinging stops.

Good luck...

UKPaul

When adjusting point gaps the timing will be altered also. This "feature" was used on old M/cycles that had 2 sets of points driven off of one lobe. You set up the correct gaps on both, then the ign. timing on one set & then fine tune the ign. timing on the other set by adjusting the points gap. Primitive, but in them days 2 cylinders was high performance stuff :D

74-Roadster

Several questions for you, I just got done doing all of this when I installed a Crane vacuum advance kit and new springs in my distributor. What gap are your plugs set at? Have you replaced your wires, plugs and points? Did you set the gap on the new points before installation and then measure the dwell? What is the mechanical advance with the dwell at 25 deg?

I didn't gap my points prior to installation and the car started up just fine, when I measured the dwell, it was 40-41 and I had to back it down to 29-30 but I don't recall it affecting my initial timing at all. . . During all of this, I had the vacuum advance removed and plugged.

After you get it set at 24-25 degrees, pull the points out and measure the gap. When you are measuring the dwell, I believe you are getting the actual duration of contact of the points to produce a spark, so I'd think that worn lobes would still allow you to set a proper dwell, but with an incorrect gap. Time for me to go read the book again.

JSB69

Try another dwell meter or make sure you are hooking yours up properly. Dwell is strictly the amount of distributor rotation during which the points remain closed measured in degrees.

lars

Steve -
Two things can be happening:
First, and most common, your dwell meter can be bad. I've seen an amazing amount of faulty dwell meters - most recently I bought a brand new Craftsman analog engine analyzer, and the dwell meter was off by over 10 degrees(!!). Borrow another meter and compare the readings of the two. If they're different, obviously one of them is bad.... don't be surprised....

Second, keep in mind that your timing will change one degree for every one degree change in dwell. As dwell increases, timing retards. So if you're adjusting the dwell from 25 degrees to 30 degrees, your timing is retarding 5 degrees. This can cause the engine to die. So advance your timing a bit, set the dwell to 30, and then final-set your timing after the dwell is locked in. But first, check that dwell meter against another one, otherwise both your dwell and your timing are going to be off....