MFI Thermostat Clarification

David E. Clark · 05-08-2003, 06:20 AM

I took my thermostat out last night for cleaning and noticed that the order of my spacers is slightly different form the way they are shown in Warren Hall's diagram in this thread:

'73 MFI Thermostat question

In my car, 1973 911E, I have two thin spacers following the spring retainer then a thick spacer followed by the series of thermal disks. My questions are, is the sequence shown in Warren's diagram, spring retainer, thin spacer, thick spacer, thermal disks, the only proper way? Should I have two thin spacers? Should they be together before the thick spacer? Will the function of the thermostat suffer if the sequence is not exactly correct? How? The "check, measure, adjust" book says: "if the expansion elements or disks are mixed up, the warm up characteristics of the thermostat will be changed." Doesn't cleaning all the goop off the thermal elements change the "warm up" characteristics anyway? I'm pretty new to MFI so any help would be greatly appreciated.

Thanks,
David Clark
1973 911E, Targa

P.S. I can't say thanks enough to Warren Hall, John Walker, Wayne and all the other experts on this site. I bought the factory owner's manuals, and just about every other book I could find (101 Projects is wonderful) but I keep coming back here because of the expertise!

David E. Clark · 05-08-2003, 11:30 AM

OK, maybe if I add some more information someone might have an idea or answer. I'm getting moderate amounts of black soot on the plugs indicative of rich running. No fuel smell in the oil. The car is a little slow to start (usually two tries, never more than three) but has good power at all engine speeds after warm up, no missing or backfires and reasonable fuel economy. The "problem" is not too serious -- but still!

Before messing with the MFI, I thought I would try the other possibilities (as has been suggested on this board). Checked compression, all W/I 10%. I changed the plugs and wires, installed a K&N filter, replaced the hot air hose to the thermostat, cleaned or changed every ground and electrical connection I could find, including changing the transmission ground. I did this to assure that the CD ignition was operating up to it's full potential. Made sure the batteries were fully charged. Checked the timing, point gap and dwell. All OK. I am still getting black soot! I saw Warren's advice about cleaning the thermostat and decided to try that. I noticed that I have two thin spacers between the spring retainer and thick spacer. In Warren's diagram, there is only one.

Since the expansion of the thermal disks must be very small, could some previous owner have inserted a second thin spacer in an attempt to lean out the car earlier? If I remove this second spacer will my "problem" get better or worse? When I purchased the car, in December 2002, I was told that the MFI pump had been rebuilt in the not-to-distant past. Unfortunately the owner didn't have receipts. I tend to believe him about the pump rebuild however because the car does run well and the pump is cleaner than the rest of the engine. Could the rebuilder (or prior owner) have installed this second spacer in an attempt to compensate for other worn internal parts? Finally, am I making too much of the soot on the plugs? Is this something that MFI owners will just have to learn to live with? Hopefully someone will have some ideas for me.

Thanks,
David

jeff m · 05-08-2003, 04:57 PM

David,
Thought I'd give you a bump to page one.
I think your concern is that the themostat may not be leaning out the pump when hot.
Remove the small triangular plate on top of the pump and check the pin.
I assume you checked the lower hose too.
As for the washer sequence, you'll have to wait for the experts.

Jeff

Tim Walsh · Tim Walsh's Garage

David,
I think Warren or Jonny W. would know more.

If worst comes to worst we can pull mine apart since it needs to anyway and take a look.

Tim

Tim Walsh · Tim Walsh's Garage

I'm not sure if this helps or not

Tyson Schmidt · 05-08-2003, 08:01 PM

If you remove a shim between the housing and pump, it will lean it out sooner. If you remove a shim inside the housing between the thermal discs, it will lean the pump out later as well as not enough.

David E. Clark · 05-09-2003, 06:28 AM

Thanks for the replies.

If Tyson is correct, the "extra" thin spacer I have may be contributing to the rich running. I'm going to reinstall the thermostat tonight exactly as I removed it (except clean), run the car Saturday and see what my plugs look like. If that doesn't help, I'll remove the "extra" spacer and try again. I'll post the results in case anyone is interested.

David