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nkemp
03-31-2017, 02:34 PM
Heads up owners ... I checked my full throttle enrichment switch (Part#: 102785) and noticed that it was stuck closed (engaged). As such, it was always in the enriched mode. :thumbdown: If it operates normally, you should be able to feel/hear it click. A meter will tell you if it is stuck closed as well. Also, be forewarned, Those bolts securing the switch to the plate have REALLY SMALL nuts on the bottom side and fall away to unknown destinations really easy. Also, to make reassembly easier, mark your alignment on the bracket by drawing a line on the bracket next to the switch.

When I had it on the bench, the first thing to do is use a punch to push the pin the metal plate pivots on. Don't push all the way through or you risk losing the pin. Use a pliers on the last part to avoid losing the pin. If you lose the pin, a piece of paperclip cut and bent on both ends to hold in the hole will work until you decide to do something else about it. Remove the plate to get full access to the pushbutton.

Next, using a magnifier, I noticed that the rubber boot around the plunger was cracked. Also, there seemed to be something else around the plunger (retainer?) and it seemed broken. First I sprayed a bit of MAF sensor cleaner on it and the button did not release/move. There was enough of the plunger to grab with pliers so that I could give it a gentle pull. The plunger will come out 1/4" and more, probably all the way out (I don't want to pull it out in fear of it not going back in properly). I think the reason that the plunger will come out is that when I pulled the plunger with the pliers it pulled the retainer out (I no longer see the part).

So the likely failure mode was the broken retainer and sticky parts ( the switch now "clicks").

At this point, I think I'll add a dab of heavy grease (high temp brake grease) to the plunger area to keep water and dust out. Not the best alternative since it may gum it up and/or run out when hot.

Almost any normally open microswitch will work but, as is so often the case, the problem is mounting and alignment. As such, my goal is to reuse the switch ( replacements are $60'ish plus SH&H... and microswitches can be had for less than $5 delivered). I'll look around to see what I can find.

SUMMARY:
- You may not notice this unless you physically check the switch
- The parts are getting old and deterioration may cause the plunger to stick closed
- A little putzing on it can get it operational again, but repair of the failed boot and retainer is unlikely
- A little grease on it if it has failed or not may help. It may help keep the grit out. But it may also gum it up a bit and run out under high temps
- Worst case is to pull the connector until another fix is implemented . This stops continuous full enrichment but also eliminates full throttle enrichment
This picture shows the plunger in. You can also see the cracked boot. 50107
Here the plunger is up a bit50108
Sorry about the blurry photos.

FABombjoy
03-31-2017, 04:04 PM
Overly tight mounting screws can do this as well. It'll be fine until you go WOT and then it can stick closed. I learned that the hard way!

Horsebox
03-31-2017, 04:05 PM
Great post!

I've had both metal plungers out of mine (auto) and it was no drama. My boot looked the same as yours too. I was just going to replace both switches until I saw how much they cost.

I found that if you tightened the main bolts too tight then the switches would remain jammed ON.

FABombjoy
03-31-2017, 04:07 PM
And in lieu of a mechanical switch, has anyone switched to a Hobbs vacuum switch? I purchased one set for 2Hg but then I tore out Kjet before testing it.

dmcindiana
09-08-2024, 11:57 AM
Found this discussion after discovering my plunger was stuck open. (Manual, only one switch.) In my case, after playing around with it, I realized my plunger would also come out as far as I wanted to pull using a tiny flathead screwdriver. So as the OP said, I stopped for fear of it coming all the way out. Pushed it back in and now it clicks in and out nicely after just some back and forth to get it moving. No removal, no grease. Continuity is good, armature engages it nicely. I?m not messing with it further.

The metal flap, though. Is it supposed to freely swing a good 3/8 inch or more? Seems weird. Why isn?t the design to keep it held in place just a hair from the open plunger?

David T
09-08-2024, 12:23 PM
For those with an automatic transmission where you have 2 micro switches (one is to force a downshift and the other forces open loop full rich) you can have a problem with the transmission. Just hearing the switches click is not enough. I have seen where they will click but electrically do not change state. Best to use a meter, confirm the click and verify a change in state with a meter set to continuity. Also verify when the accelerator is fully depressed you have WOT. Check for play (looseness) at the ends of the quadrant link (that short link between the throttle spool and the throttle arm) and that the throttle spool moves smoothly. On many cars that grease in the throttle spool has turned to a sticky mess and needs to be cleaned and regreased after 40 years. There is also a procedure (a recall in fact) for lubricating the throttle cable. The switches can also be damaged by being poorly adjusted. Any movement to "click" the switch must stop once the switch has clicked. Pushing the plunger past that point can damage the switch just as the mounting screws being over-tightened will damage them too. While you're at it check the switch for the idle circuit.

dmcindiana
09-09-2024, 02:03 PM
David, I appreciate the info, but my question was just about the metal flap. Should it have about 3/8 inch of free swing, just kinda flopping around, or is there supposed to be something holding it in place just in front of the plunger?

dmcman73
09-09-2024, 04:03 PM
David, I appreciate the info, but my question was just about the metal flap. Should it have about 3/8 inch of free swing, just kinda flopping around, or is there supposed to be something holding it in place just in front of the plunger?

Free swing, it gets pushed up against the small button the same regardless if it was swinging freely or sitting tight against the button.

dmcindiana
09-09-2024, 07:03 PM
Free swing, it gets pushed up against the small button the same regardless if it was swinging freely or sitting tight against the button.

Appreciate it!