MFI questions

huduguru · 04-06-2002, 07:55 PM

I have a 73 911T that came out of a brief stint in storage-2 mo. She needs a tune up and will get one, but I checked the vacuum tubes on the #1 and #4 stacks and the look cruddy--not much vacuum there I don't think. She pops a little after letting off throttle going down the road--I wondered if the distributor was not able to advance due to less than desirable vacuum--

I've read Lee Rice's MFI articles several times, and they say if those vacuum tubes are plugged, the stacks need to come off and the 4 (2 on each side I guess) inlet holes will need to be reamed with a #41 drill bit.

Do the stack assemblies need to come off to do all this or can one fish a wire in the brass tubes and clean the holes? Warren, you've probably been down this road before--What are the torque ratings on the nuts that hold the lower stack assemblies to the heads?

Thanks in advance-
JW

Early_S_Man · 04-06-2002, 09:15 PM

John,

That sounds like a possible failed speed switch, or maladjusted microswitch, rather than related to those vacuum ports! Put a test lamp or Voltmeter on the cut-off solenoid terminal and rev it up past 2000 ... then back off the throttle while watching for solenoid activation ... it should immediately come on when throttle lever goes back to rest, and lose the 12 Volts after rpms get down to 1300 rpm.

If the speed switch is the problem, it can be repaired, as the Siemens transistors used were mfr'd with leads that were gold-plated iron wire, and the wire corrodes and fractures due toexposure to the elements and engine vibration. As far as I know ... nobody has found anything wrong with the speed switch EXCEPT loose transistor(s) rattling around inside the case!!!

The distributor doesn't need any vacuum except at idle for 10° retard to improve emmisions compliance. At any significant rpms above idle ... the advance is all centrifugal. My recommendation is to remove the distributor at TDC #1, and do a thorough cleaning and partial disassembly. Be sure to check end play on the shaft ... it shouldn't be more than 0.004", unless the phenolic-fiber washers are worn or gone! The following thread has all of the specs to check the complete advance curve:

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=5432

huduguru · 04-06-2002, 09:45 PM

Thanks for the quick reply Warren--I'll check the voltages and watch for the activation/deactivation.

I do want to verify I reassembled the thermostat correctly however--The discs were a little stuck together, so i cleaned them, and reassembled, making sure they were in the alternating pattern, but my question is on the ends of the discs: there is a thin and a thick flat disc--I put the thin one, which didn't have the small bump like all the regular thermo discs, on first, towards the tranny, then started the alternating discs. At the rear of the series, I put the thick disc on (looks like 3 discs put together), followed by the tin spring retainer, then the spring, then the end cap. Was this correct? I'll shoot you an email--

Also, my ICQ was hacked-someone from Istanbul took my number over. So, you can delete me on your end for now until I get a new one....JW