mystery of the missing mark, who dun it? the distributor? Options

[iankarr]

Hi Guys,

I noticed when tuning the carbs that the #2 mixture screw had no effect. Car had occasional mild backfiring on deceleration. Checked the plug and it was sooty. Replaced the plug and #2 seemed normal. Mixture screw set properly. Drove for about an hour and #2 is out again (pulling the wire has no effect on idle).

Hooked a timing light set to 28 degrees on the #1 cable, aimed at the viewing port on the flywheel and see the factory TDC notch when at 900 rpm idle. at 2500 rpm I see only a circular divot, which I assume was drilled out in the process of balancing the flywheel. (Same deal with the fan markings, but my aching back prefers using the flywheel mark).

I did have the distributor out over the winter, but was super careful about marking its position and replacing it. Doesn't seem to be 180 out, as the engine runs pretty smooth otherwise. But with #2 acting up, and the disappearing timing mark, I'm now suspecting that something is amiss. Pun intended (IMG:style_emoticons/default/wink.gif)

From the day I got the car, the #1 spark plug cable was where the # 2 would be on a stock dizzy. FYI it's a 2056 motor. Compared to the Haynes picture, starting at the wire closest to the fan, you might say the cables are 4-3-2-1. I tried moving the all the cables over one space clockwise so it's 1-4-2-3 but got no start and backfires. I don't know if that's because the cables are now in the wrong place...or maybe they're (finally) in the right place, but the current position of the distributor is too far advanced or retarded to work properly.

I'd like to reset the position of the distributor just to make sure I'm starting from baseline. Any tips or tricks to do that?

I've also got a new set of plug wires on order from Tangerine, along with a new rotor and cap.

Thanks for helping me get to the bottom of this mystery!

[cary]

I'm no help ...........
But Mark's blue car is a 2.0L with carbs. His #1 is in the same place as yours.
But his fan had no timing marks (bus fan). And only one mark on the flywheel.

[iankarr]

Thanks, Cary. That actually is a help! Nice to know I'm not alone.

I think I may have found the cause of the miss...seems that the spark plug insulator (NGK plastic type) on the wire leading to #2 cyl was cracked. I should get the new wires by wednesday, so we'll see if that makes a difference.

What I'm still scratching my head about is why the timing mark on the flywheel disappears at 2500 rpm.

[stugray]

If you are using a variable timing light set to 28 degrees and you see the timing mark at 900 RPM, then that is your timing at 900.

As you increase RPM you will increase advance depending on what kind of dizzy you have.

Get the engine up to 2500 RPM, then turn the dial on the timing light until you see the TDC mark again. Whatever the timing light had to be turned up to is now your timing at 2500 RPM.

[iankarr]

Thanks so much for the response, Stugray!

I tried your suggestion...but I can't get the TDC mark to appear again at 2500 RPM, even at the upper limits of the gun (and another one I tried). FYI, It's a Unilite dizzy without vacuum advance.

What's puzzling is that, if the engine is really so advanced at 2500 that I can't get the timing light to see it, it would be pinging like crazy, no?

I'm going to try retarding the dizzy at 2500 and see if I can get the mark to appear. But I know when I backed off at 900 the engine didn't like it.

So weird. The engine sounds fine, pulls strong and doesn't overheat. I'm guessing it's in the ballpark of where it should be. I just can't get the timing light to agree.

I'm probably just doing something stupid.

[stugray]

Do you have a MSD?

I have heard that certain timing lights cant handle the double pulse from the MSD ignitions.

The MSD is supposed to stop the double pulse at something like 3500-4000 RPM.
Maybe see if the mark appears again at higher RPMs?

I have the Mallory unilite with MSD and my variable timing light seems to work fine

[iankarr]

No MSD. Been thinking about it tho (IMG:style_emoticons/default/wink.gif)

I've tried two coils...stock blue (new brazilian one) and an Accel coil. The dizzy has an accel ignition model 2005 inside.

I'm gonna change the rotor, cap, wires and plugs and see how that goes.

Thanks much!

[ChrisFoley]

Maybe the advance range in the distributor isn't adjusted right.
Try setting the timing at idle using 12 degrees of advance on the timing light, then check total advance at 3500.
(The mechanical advance should not be all in by 2500.)

[iankarr]

Thanks, Chris. Good idea(s).

Will try setting to 12 at idle and see what happens. I'm sure your new cables will make things snappier as well.