Help - Djet running way too rich Options

[Halfnelson]

Help - my new to me 1973 1.7 Djet came running really sweet, but almost immediately developed the 'hunting tick-over' of lean running / air leak. We replaced all the vacuum pipes, found one of the inlet gaskets had a very slight leak. Seems somewhere along the line things have been tweaked to compensate for the leaks so that now they're cured, the car is running super rich. Having had a L-jet for years the Djet is new to me so any advice on where to start first would be much appreciated. Thanks Chris

[jrmdir]

Hi Halfnelson: Hope this doesn't amount to hijacking your thread but since we seem to be in the same boat maybe my experience so far is of interest. (I had no knowledge in this area a month ago so take my advice with a grain of salt.) But the huge body of work on this forum has been very educational!

As advised above, I did start with valves and ignition. PO had replaced all spark related parts and I reset the dwell and timing to spec. I also installed a fuel pressure gauge and lowered it to just under 30 PSI. Next I pulled the throttle body and checked cleaned and adjusted the TPS contact tracks.

Next up, the MPS and sure enough, mine held no vacuum at all. So I replaced the perished diaphragm using TR's kit. Successfully but still in question (see below)

Next I removed and tested the Aux Air Valve - it worked but I decided to leave it off and plug the manifold outlet. Ditto with the Decel Valve. Unlike more modern FI systems with mass air flow meters, a downstream vacuum leak on d-Jet shouldn't cause a lean condition. The MPS will note the pressure drop and add more fuel. BUT, this should be in proportion to the "extra" air so it shouldn't be richer. I think:) Anyway, based on what I read it was OK to disconnect these for a while to reduce the number of variables. I may hook them up again later.

Then, to eliminate doubt re: defective Thermo switch or leaking cold start injector, I got a 3' length of fuel hose and completely bypassed the injector.

Finally, (and I should have done this earlier,) I pulled the ECU connector and performed all of the circuit tests described in the rennlist bpanders link above. Was hoping for a smoking gun test result but everything checked out. (Although I'm still questioning CHT reading of 2,250 ohms @ 78 degrees F. Seems a bit high to me.

So now I'm down to one question that perhaps the group here can help us with:

In rebuilding the MPS, reestablishing the height of the center plunger involves an imprecise measurement. So this could be the issue. There is mention of uncovering the adjustment screw and then calibrating the MPS. But Mr Anders says this requires special equipment. It seems like this adjustment could easily impact the rich/lean situation. Has anyone tackled this calibration without test equipment?

Again, sorry if this is a hijack but hope our shared experience helps someone now or in the future.

Good luck!

Ron