I thought I would show a few pics of the tool set I made to overcome the MPS tuning. Note I started with an inductance gauge and vacuum line to make graphs of the changes induced by vacuum. This served as baseline out of the car. Then when the car was running I used these with the MPS in place:
The kit has three pieces, plus an MPS mod through the cap (red plug).
First there is a small screw driver for the main adjustment screw that alters rich vs lean.
Second is a 7 mm nut ground to fit ito the hex of the aluminum diaphragm adjuster stop. The nut is soldered to a tube and a plumbing piece as a handle (I used stainless steel braze -orange$). The nut is drilled out to allow the screw driver access to the screw.
Finally a scrap of 18 ga steel in a wood handle for the cap screw that adjusts where WOT ends up.
There is a red plug in the aluminum cap. The cap has been drilled as can be seen here:
The shoulder is still on the plug, and in this MPS the hole does not make an air leak. It would be air tight with the simpler versions on Ca '69 type 3 and 4 models.
Here is a shot showing the hex end and the screw inside it. Sort of like valve adjusters.
And here we go. Normally this would be a hot engine bay. It is important to have all three screws right, but I used the outer plug and the inner screw had the most impact. I found it very helpful to be able to make adjustments without disturbing the outer stop, so I needed to have a hole through it so any of the three screws can be moved without moving one of the others, and also in short increments as you pull over and try to find the right setting.
You want to seat the hex first and then find the slot for the screw driver. I tried to make it so I could turn the small screw while holding the aluminum one still.
I just bought a non-working type 3/4 on ebay without the secondary diaphragm that Racer Chris sells (thanks!). It can be fixed and I will give it a try.
Please do post about the Type 3/4 MPS...I've got a used one of those as well that I've been wondering about. I do think Chris Foley had tried one of those in his car and wasn't able to tune it right....I'm not positive though. I've seen SLITS mention them before so it would be a good project to try. Jon
Creative! But why not just get the MPS tools from Tangerine? They are excellent and affordable.
Thats cool...you did it beacsue you could...[applause]. Ah, but that big hole in the WOT stop will be hard to seal too. What was your thesis on?
I can't say about your 'engine harness', it all depends on its condition. I assume you mean the FI harness? The boots perform four important functions: they protect the bare wires from heat damage, the electrical connections from dirt/moisture contamination, provide stress relief for the wires, and they keep the connector plugs secured to their components.
I'd give you half a core value for a 1.7L core towards a 2.0L harness, if it has a 4-pole TPS, otherwise full core value.
You graphed the curves? Then wouldn't it be a relatively easy thing to use a MAP or some other vacuum sensor to recreate the MPS functions in an electronic module? Replace the MPS altogether?
I don't have an MPS so this isn't a concern for me, but do you know how many MPS threads there have been over the years? What will happen when you can't find functional units any more, how to rebuild them, what alternatives might work, and so on. Seems it would be worth someone's time to put together a little electronic unit that just produced the needed signal without too much muss or fuss. And not just 914's, also the VW T3's/T4's, Volvos, etc. Just an observation. From ignorance, probably.
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