318 Engine stumble

[glhx]

When this distributor came to me. It came with the cap facting the front of the engine

It occurred to me just a few minutes ago that I have never seen a cap set up like that on a gm. I didn’t catch it.

When I looked at the distributor housing. It has a notch for two cap placements. One to the front and one to the side. I’ve never seen one like this....if I did I didn’t know it.

When I turned the cap to the drivers side.....rotating it 90° the mark went to the left about 1/8”. I think that would put it back into phase.

Now that I have repahsed the reluctor....I don’t know for sure. ....
But logic would dictate this is correct. I think this was out of phase because the cap was set the wrong way....and it did come that way. The top picture shows how it was sold to me.

This picture shows how it should be

This is the new mark.....the thin line.
The old mark where I had the cap facing the wrong way is the thick mark

This shows the two notches for the different cap placement. The upper one is with the cap placed forward toward the front of the car......the bottom one is true TDC.
The new thin line is closer to the middle and is not drawn in here

Looking at it with the sideways cap placement. It’s still would be out of phase. Just not as bad.
Instead of relocating the vaccum advance. I could have extended the notch in the distributor housing and rotated the cap.

What would this movement have changed. It might not be backfiring because it would be closer to the #1 than the #8.
But it would still have pretty far for the spark to travel.

Looking at the previous pictures where it was original before I messed with it. Those pictures might tell. It might put it on the leading edge of the points or might even put them in contact.......not really sure.i think this might have been the problem all along.

Thoughts on this?

 

[glhx]

I bought a new distributor.
This one seems a little bit better, but I thought I would just set it in at TDC and see where it ended up before I ran it. It still seems off....

It seems like 16° Advance puts tdc in between the spark towers. It would fire at 16 and by the time it hits TDC it’s in between the spark towers 1 and 8. It’s a pretty close guess given that the distance between towers is 45°.....the halfway point is 22.5 so I went a little less than that just by looking at where TDC is and where 16° would end up. It’s probably close. I hope I said that right.

Look at the TDC vs cap placement.....the rotor seems to start the firing at the trailing end of the contact sweep. This is something I don’t know enough about as far as phasing. I would think it should start at the leading edge going into the sweep.......
Should it be on the leading edge?
or should the rotor line up right in the middle of the contact sweep.
......or is it sitting in the right place where it’s at at the end.

As I said before. The other distributor aligned TDC to the cap a little better at the sideways position like a chevy does. This doesn’t work on our cars because we have the kick down linkage there. It has to be in phase with the distributors’ electric hook ups facing the front of the engine .........it has notches to do both ....front and sideways....even though sideways won’t fit a mopar with a kick down....

Once I know where the rotor is supposed to come into the firing sweep on the cap....if the trailing edge is wrong. I can turn the cap 90 or so degrees and put in a new cap notch.

I have not run it on the car yet

This is sitting with the pole piece lined up for TDC.

This is sitting with the pole piece lined up at about 16°
Which puts TDC between the towers.

Is this ok?

Also....This one is in an entirely different clock position as the last one. The last one was pointing to the drivers side head

This one puts TDC to the passenger side head. It can be reclocked easily but it showed that it varies on how these two were machined.its a different manufacturer
And seems to have even less quality than the first one.
It has no grease on the weights.
The weights are thicker and heavier
The collar on the bottom has about 4 shims and a plastic collar.

The other one above has a metal collar with 1 shim and was greased. The boxing was much higher quality as well on the first one.

 

[nm9stheham]

One thing to change in your thinking.... the distributor turns at half the speed of the crankshaft. So 16 degrees of ignition timing change will be only 8 degrees of rotation on the distributor.

If I understand yo right about the position of the rotor when it fires, if there is no advance, then it should fire when the rotor is just past the tower. Then as timing advances, the rotor will be more and CCW as you view it from the top, or more to the right relative to the tower when viewed from the side.

 

[glhx]

I’ll have to think about the half speed a little more critically. I’ve never thought about it like that.

It seems that way.....About the rotor position as you stated above
It looks like the distributor at 0° fires right after the sweep.....right on the edge of it. It’s close enough to make a spark jump but not in phase like a mopar distributor. I have not played with it completely yet. I guess the Chinese didn’t have a 318 when they made this.

There is a lot of rotating play in this distributor. It makes the timing marks jump around more. At least I think.....it could be that plastic coated timing chain. That thing has to go. I checked the other three
(Points, electronic, red cap Hei) distributors and they had some as well but not as much. The red cap Hei had the least and had a deeper tab to go down into the drive gear. Aside from the phase problem.....the red cap seems to be of decent quality for what it is.

I set it at 16° and fired the engine. While the engine was warm......it did not backfire out of the intake. I did not get to mess with it cold. I ran out of gas and was done with it for the day. I ran it just enough to burn anything off the plugs from the previous attempts.
This little engine really likes 16°.......I don’t know what it is. It had crisper starting and you could tell it had more power.

.......it also seems like the idle transition is better. The reason for that could be that I took the carburetor off and replaced the gasket. I sprayed some wd40 on it as the non stick gaskets......stuck. Spayable lithium Grease might be better...l removed the carb to check the transfer slots. They were perfect. I closed down the secondaries as closed as I could get them without them sticking.....which could be why the transition is better. I don’t remember where they were but they are closed very slightly more. A vacuum leak is a vacuum leak. The less air through those the better.

I put a factory electronic I have sitting around, back in to see how the phase lines up. It is spot on center of the sweep. Where as the Hei distributors are not. This seems to be a problems with the HEIs...
The electronic needs to be redone and set up for total timing and Hei, not using it now....but I do plan on using it sometime down the road. It’s probably got 30° of advance built into the unit. It’s from 1976. The spec is probably at 850rpm is probably somewhere around 7°. It has quite a bit of extra parts that go with it to make it Hei.....it’s more accurate and smaller so it seems worth it.

If I can get this thing total timed.....I can start working on the curve
And learning about how that graph should look. This thread has become really long. I might do a different thread for that. The original problem in the title.....is finally gone. Jet change, accelerator cam change and closing the secondaries seemed to be the solution for that.....