1973 911E MFI adjustmet

[Jeff777]

Hello all

I have the above car and just had the engine completely taken apart and reseal done with tuning of the engine by a very qualified tech. It now runs great except for low rpm/low gear when it is difficult to accelerate slowly without it bucking and coughing/backfire. If I hit the accelerator it clears. Otherwise car runs great...solid idle at 1000, starts well and very strong pulling. The tech used a gas meter to set the CO at 2.7%

I have gone through the CMA and am now at part load test and adjustment. Just bought an Innovate LM2 and have it hooked up.

So, my question is how to do the part load test? I know it's 2nd gear, 2400 rpm but the rest is pretty grey. Is the test done on level road, downhill with brakes or uphill. Any advice much appreciated

Cheers
Jeff

[30westrob]

I have never had the luxury of an exhaust gas meter, but I have had good results with trial and error. It sounds like your part load is lean. I would start with two clicks rich, and drive the car. If the lean diagnose is correct you should see an improvement and go from there. Always record all adjustments so you have the confidence that you can return home, if needed. You can probably make a few adjustments to part load, without having to adjust the rack adjustment. Rob

[nickelplated5s]

There's a reason 'qualified techs' don't touch MFI's, mine won't. Read the Rice paper. Air screws and a snail air flow meter are easy. Listen to 30west if you want to mess with the rack. There are only 3 people, companies, I know of for rebuilds. Mines been in since April 2025 and I should get it back next week or so. Then it's off for dyno work. Remember, MFI motors run what is considered dirty these days. Perhaps 12 MPG if you're on the throttle.

[PeteKz]

Jeff: Do yourself a favor and install a AFR meter. Then you will know what's going on while you are driving it, and what needs to be adjusted.

[stownsen914]

Once you have the AFR meter hooked up, just observe the AFR during the conditions when the car isn't running well, and make adjustments to make the problem(s) go away. Low RPM / low load in your case, sounds like.

There are two external enrichment adjustments on the MFI pumps. The main circuit adjustment is the one under the allen head screw. The "idle" adjustment is the spring loaded hex head thingy on the rear facing end of the pump. The idle adjustment actually covers lower RPM and part throttle usage, analogous to the idle circuit on Webers. From what you describe, you may need to adjust your idle enrichment. Remember that for the idle circuit, to enrich, press it in to engage and turn clockwise (note that this is the opposite direction of the main circuit adjustment). You'll feel as the detent clicks.

Your AFR meter will tell you if that's the adjustment you need to make.