MPS, Rebuilding the MPS Options

[Ron914]

Hello to all who have helped me with this project . @emerygt350 ,@TJB/914, @Superhawk996 , @ChrisFoley , @rjames , @MDTerp
I am in the middle of rebuilding my MPS and have a couple of comments and questions .
First when I opened up the unit I found the most difficult job was removing the rivets holding the two halves together.
When I removed the retainer plate to take out the old diaphragm it was in two pieces .

I needed to take two measurements since I was replacing the stop screw , I needed to measure the the stop screw protrusion into the housing . The instruction sheet sent to me by a member had the measurements he must have made when rebuilding his MPS . His stop screw protrusion was 1.97mm and mine only measured 1.72mm.
His inner/outer screw assembly depth in the old diaphragm measured 6.51mm .
Here's one of my questions ?
when I measured mine I got two measurements depth to inner/outer screw assembly was 4.03
and depth to the washer outside the inner/outer screw assembly was 5.46mm.
Again there is a difference and since mine was never accessed before (epoxy over screw was not disturbed) is the difference in measurements ok and which measurement should I use I will try to attach a photo or two to help with my question.
this one .

I have not touched either of these measurements yet and awaiting any help/comments.
I think it's this one to the washer on diaphragm .

[Superhawk996]

I would open the MPS back up. I can post time lapse video of my MPS if necessary. It doesn’t leak down. I may have reused the OEM rubber seal - can’t remember for sure. I know from experience experience they leak if not assembled properly.

I wouldn’t worry about changing the plugs yet. Get it running better 1st. I’m old school - the way to test plugs is remove them, hook to spark plug wire, use insulated gloves or tools, hold metal part of the plug to the engine / ground, cranks the engine and watch for a bright, hot blue/white spark. Intermittent, weak yellow spark is bad news. Spark not jumping cleanly from the center electrode to the ground electrode is bad news. Seeing the spark as it jumps the gap gives you a lot of information. SAFETY NOTE: don’t do this right in the vicinity of the cylinder bore where fuel vapor may be. Fan housing is a good ground and a safe distance from cylinder opening. Better yet - disable fuel pump while doing this by pulling the pump relay.

With respect to the ECU trigger points - just rotate the engine about 1 revolution and verify both sets of trigger points are working. They alternate. One set open, once set closed. The more important thing is to be sure your electrical spade connectors from the wiring are right on the trigger points and making good contact. I doubt anything in the points themselves has changed from when it was runnning last.

Check your FI grounds.

That Pertronix box looks old, shop worn, annd doesn’t indicate igniter 2 or 3 so I’m going to assume that’s an original subject to burn out and flaky operation if ignition left on. Personally, I would stick with points for now while troubleshooting. The original Pertronix is a deeply flawed design in my opinion given that it can be damaged by leaving the ignition on. It’s a black box - you can’t see or measure what’s going on inside.

If you do the visual spark plug test and have a good strong spark with the Pertronix in place - then leave it. Just be aware of its flaws and keep the ignition off while you are doing other troubleshooting lest it go bad in the middle of the troubleshooting and cause more confusion.

[Ron914]

I would open the MPS back up. I can post time lapse video of my MPS if necessary. It doesn’t leak down. I may have reused the OEM rubber seal - can’t remember for sure. I know from experience experience they leak if not assembled properly.

I wouldn’t worry about changing the plugs yet. Get it running better 1st. I’m old school - the way to test plugs is remove them, hook to spark plug wire, use insulated gloves or tools, hold metal part of the plug to the engine / ground, cranks the engine and watch for a bright, hot blue/white spark. Intermittent, weak yellow spark is bad news. Spark not jumping cleanly from the center electrode to the ground electrode is bad news. Seeing the spark as it jumps the gap gives you a lot of information. SAFETY NOTE: don’t do this right in the vicinity of the cylinder bore where fuel vapor may be. Fan housing is a good ground and a safe distance from cylinder opening. Better yet - disable fuel pump while doing this by pulling the pump relay.

With respect to the ECU trigger points - just rotate the engine about 1 revolution and verify both sets of trigger points are working. They alternate. One set open, once set closed. The more important thing is to be sure your electrical spade connectors from the wiring are right on the trigger points and making good contact. I doubt anything in the points themselves has changed from when it was runnning last.

Check your FI grounds.

That Pertronix box looks old, shop worn, annd doesn’t indicate igniter 2 or 3 so I’m going to assume that’s an original subject to burn out and flaky operation if ignition left on. Personally, I would stick with points for now while troubleshooting. The original Pertronix is a deeply flawed design in my opinion given that it can be damaged by leaving the ignition on. It’s a black box - you can’t see or measure what’s going on inside.

If you do the visual spark plug test and have a good strong spark with the Pertronix in place - then leave it. Just be aware of its flaws and keep the ignition off while you are doing other troubleshooting lest it go bad in the middle of the troubleshooting and cause more confusion.

I appreciate your information . I figured that was how I should test the plugs but wanted confirmation . Good idea about the fuel pump ,don't want to start a fire . I unfortunately already put the Pertronix back in . Because of what I read I jump to turn off the ignition while I am in the engine bay if motors shuts off while I am messing around so I will be careful. I do carry a set of points/condenser/feeler gauge in my cars tool bag just incase,
I will recheck the trigger points I did verify the markings on the wires go to the correct terminals on the dizzy and good connection is being made . I need to reconnect the ECU and reinstall in its location today before anymore testing ,I also will use the old plugs ,I really did not want to put my new plugs in just yet until I get this problem figured out . I will need to order a new set for my tool bag .I will need to find someone to crank the motor over for me so I can test the plugs , I do not have one of those remote starter switches but that sure would make this easier because I usually only have myself for these things . I was thinking of opening up the MPS later today ( I really didn't expect to see so much leak down after replacing the diaphragm . I am almost 99% certain I replaced everything correctly in order . Paper gasket went in first then diaphragm then metal ring . The only suspect to me was using the new round rubber gasket over the old square edged gasket .The small ring was replaced on the big screw as shown in the diagram. Should I reapply more bearing grease to the paper gasket? I wouldn't think the settings I took and used for reassembly would cause a leak ? I will update this post as soon as I can get to these new things to do .