Workin through the 2500 RPM shudder on my 2.0..., Next steps???? Running out of ideas! Options

[jk76.914]

I'm slowly working through the 2500-3000 RPM shudder that I get in my 2.0 at part throttle cruise... It's a '76. The engine has 850 miles since the rebuild. Rings seated very quickly- no oil required from its 250 mile oil change to its 850 mile oil change.

Also, during the rebuild, ALL ground connections were carefully polished, and assembled with star washers on both sides of harness lugs. Also, injectors were rebuilt and calibrated by Marren Fuel Injectors in Connecticut. Cap, rotor, plugs, wires, coil all new. It's got a PerTronix pointless ignition.

The car runs better than new at all RPMs and load, except for this shudder. Sometimes its less noticable than others....

WHAT HAVE I MISSED HERE!?!

So far, I've gone through these steps-

1. checked and adjusted fuel pressure. Was running 34 psi. Reset to 29 psi.
2. checked and adjusted timing at 3500 rpm.
3. adjusted TPS at closed throttle using Pelican Parts procedure.
4. Tried warming up, then disconnecting TPS and test driving. TPS seems to be doing its thing... Ordered a new TPS anyway, since mine is old, and they may be hard to find in the future when I really need one, and I can use the old one for a spare. Not in yet.
5. connections through 270 ohm resistor and into TS2 are new and sound.
6. measured TS2 at 80 ohms hot, 2200 ohms cold. Engine had already cooled a bit before I could get my meter on it, so the 80 ohms may be a bit high, but looks fine. TS2 was new 850 miles ago.
7. disconnected vac retard and test drove. Aside from high idle, it still ran the same, ie still had the shutter. I thought that since rebuilding the dizzy the breaker plate could be moving TOO easily, and there was maybe an oscillation set up because the vac port in the TB was partly exposed to vacuum at 2500 rpm third gear cruise. Anyway, still ran the same.
8. New Bosch FI breaker points.
9. Since the '76 didn't originally have the 270 ohm resistor, I tried shorting around it. It ran very poorly across the range, especially cold or warm.

Also, I bought an inductance meter to check out my MPS. Mine was a rebuilt from AA that I got in about 1989. I have no idea which one it is or was, so I'm looking forward to finding out and adjusting if necessary to '74-'76 2.0 specs. (meter hasn't arrived yet)

So now I'm thinking that I may have screwed up the centrifugal advance. I built one good dizzy from two. I noted that the springs from the one were wound from two different sized wires, so when I assembled my composite one, I put two same size (smaller gauge wire) springs in.

So, I MAY be getting too much advance in the range where I'm having the problem. Looks like the '76 2.0 got a lot less advance until 3000 RPM than some of the other D-Jet dizzys. My original was '76, and my donar dizzy was a '74 2.0.... The easiest and most precise way to know what's going on is to take the distributor somewhere and get it plotted.

Can anyone recommend a place where I can send my dizzy to have the advance checked and calibrated? Preferable in the Boston area, but I'm glad to ship it if the turn-around is reasonable.

THANKS!

PS- ANYTHING I MISSED HERE??? ANY MORE SUGGESTIONS ARE WELCOME!!

Jim

[jk76.914]

An update. I think progress is being made...

To test my theory about distributor advancing too quickly vs. RPM, I retarded the timing. The shudder is still there, BUT! the engine runs much more smoothly and is quieter at idle. Plus, at WOT and >3000 RPM, it actually seems to be pulling stronger.

Still looking for a place to check my distributor advance.....

Next steps here- verify that the paint mark on the pulley aligns with the groove on the fan casting at 27 degrees. This fan is not the original, because the original one to my engine had 3 or 4 broken blades. Though I had the replacement one balanced and it's pulley trued on a lathe, AND I verified that the TDC mark on the fan was good, I never verified the paint mark on the pulley. To verify the TDC mark, I found TDC with a vernier depth gauge before the head went on. The TDC mark aligned perfectly with the fan housing, as did the TDC mark on the flywheel..... Anyway I'll do that this weekend... use a mirror to see the fan markings, align TDC and put a new paint mark on the pulley, and then find 27 degrees and put another new paint mark on the pulley....

Also, my LC meter arrived yesterday. I did a quick check on inductance at 0 inches Hg, and whatdayouknow? 1.45 H. EXACTLY the inductance Paul Anders specified for a -043 MPS (after correcting his 1.39 H for sea level, where I'm at).

That was great news, but that's at 0 inches, and my problem is at part throttle, probably 6-12 inches. But at part throttle, the inductance is varied only by the aneroid cells, and if one or both were leaking, I think I would see less than 1.45 H, so I think my aneroid are OK, and since the MPS holds a vacuum overall, it should be adjustable if it's out at the other vacuum levels.....

Those are the next steps, which will have to wait for the weekend....

Does this make sense or is it just my imaginative misinterpretation of the engineering involved????

Comments are welcome!
Jim