MFI "Check, Measure, Adjust" Questions
 

Hey MFI guys, I'm going to start tuning our 73E and, as a part of this effort, I intend to check out our MFI setup. I have been studying the "Check, Measure, Adjust" tech note.

Q: Has anyone made their own protractors? How did you do it and what are the dimensions? I wanted to buy them (new or used) but have had no luck to date.

Q: Does the MFI adjustment procedure need to be modified for cars that have SSI's, and therefore no longer have the hose and valve-type thingie (sorry for the techie description) that goes from the air box to the left heat exchanger?

Thanks!

I didn't get past the compresion step when I went through check, measure, adjust when I did the procedure on my car and I can answer your second question but I'm not totally sure about the first.

The warm-up housing that you're refering to is for emissions only. It helps it to warm the car up quicker. I don't think it has anything to do with the check, measure, adjust.

I think for the protractors you don't need them but I don't remember exactly how you go about the procedure instead.

"no longer have the hose and valve-type thingie (sorry for the techie description) that goes from the air box to the left heat exchanger? "

That hose runs the MFI thermostat. It controls the mixture for warmup. When the engine is cold, the thermostat richens the mixure to compensate for it. When the thermostat heats up from the hot air off the heat exchanger, then it leans the mixture out to match.

Without that hose, it will either run very rich when warm, or very lean when cold. Either way, you are going to have a time where the MFI will run terribly.

Clay, I think you're referring to the narrow hose that runs from the MFI pump to the heat exchanger. That's still in place. I'm talking about the wide hose that runs from (nearly) the rear-most end of the heat exchanger thru the valve, and on to the airbox. It looks like it routes heated air to the airbox during the initial warm-up period. Of course, I could be wrong...I'm just starting to dive into this.

Any of you MFI guys use the protractors?

Thanks!

edit: I'm too slow, Clay. I see you already addressed my comment.

If you are referring to the one that runs to the intake snorkel, then no, you don't need it. It's just to warm the intake air when the outisde temp is cool. That will lower the emissions for warmup.

If you want it to work, just get one of the clamp on "heat stove" deals that are used on Small block Chevys with headers.

But I wouldn't go to the trouble.

Clay where would you get one of those clamp on shrouds? My T failed inspection because the warm up housing was not installed.

I put one on a 69 Pontiac Firebird with headers. Got it from the local speed shop so that I could pass the visual in 1988.

I think that JC Witney sells them. Or just make one. Take a piece of pipe that is the same size as the hose, and fishmouth it to fit over the side of the heat exchanger pipe. Then put 2 ears on the fishmouth end and use those to clamp it to the heat exchanger pipe. Simple but effective.

It does not have to be a tight fit, as it's supposed to take in air.

BTW, sorry for the confusion on the hose. I have to mentally reverse the engine references. After all, you guys have the engine in backwards! ;-)

Clay, "fishmouth"? Not sure what that means... Can you do a quick drawing or attach a photo?

Getting back on topic. :)

I borrowed this image from a site selling tubing cutters.

http://www.irvansmith.com/images/lowbuck_notcherB.jpg

The pipes in the picture are fishmouthed.


As for the protractors, I have not found a need for them. I take a set of digital calipers and set the rod lengths to the factory specs. To do this, measure the inside of the socket for the joint, and zero the calipers. Then measure from the inside edge of the 2 sockets at the farthest apart points. With the calipers zeroed like I said, the length on the calipers will be from center to center of the sockets.

Hope that helps.

Hal, Do you remember what paul T. used instead of protractors?

You dont need the protractors to do a good tune-up. The best thing that you can do is; remove all of the air correction screws (write down for each one how many turns it took to get it out) and use some carbs cleaner and wire pipe cleaners to clean them out really well.

Re-install and back them out 3.5 turns. you wrote down how they were before just in case you have to go back to the drawing board. Then, unhook the shafts that go from the cross bar to the throttle bodies to make sure that there is no preload on the throttle plates.

Start the car and adjust each cylinder. The book suggests adding the flow on each cylinder and devide by 6 to get the average and set then all at that. When you reattach the rods to the throttle bodies make sure that there is no pre-load or this will screw it up.

Paul

Read the other articles in Pelican's MFI Section: like this -

" The sockets are made to pop off the balls. Just wedge a large screwdriver blade between the ball and socket and twist, or use an open-end 10mm spanner in a similar manner. The length of only one rod is critical: the rod between the MFI pump and the accelerator linkage. It should be 11.4 cm +/- a few 1/10th millimeters from balljoint centre to centre. With that one set right, the lengths of all the others fall into place.

Essentially, you adjust the length of all the rods so that the butterflies are closed and each is just resting on it's stop. The "correlation" will then be right. You don't need the protractors. "

Bob Spindel
'72 911T
'73 911T

Then use a Unisyn or Synchrometer to balance air flow between the stacks - by adjusting air flow screws as warmed up (180 deg) car is running. Some people also adjust the butterflies relative to each other with a Unisyn. Read the section about part load vs idle mixture adjustment. The part load "running" mixture has to be measured under load, ie a running, driving car! Like on a dyno or with the gas tester rigged up in the passenger seat.... :eek:

The protracters are used to set the part load adjustment. Many people just use the hand throttle, set to 2500 rpm and check part load while driving. This is not correct. You should use the hand throttle to set the butterflys open the spec amount(my memory says 7 degrees but I may be wrong) drive the car(or use dyno) and brake the speed to 2500 rpm then measure part load CO. You see by setting the throttle open the required degrees the car will rev past 2500 rpm, by braking you put load on the engine. You are lucky. With the 2.4L you do not have to measure intake air temperature in combination with the CO. I have not found the protractors anywhere. But you can rig a pointer on one of the butterfly lingages and use a protracter to measure the opening of the valve as you raise the hand throttle. Good Luck

Thanks guys! A follow up question - Is the synchrometer the same as what's used by the carb guys? Or is it a different model? Thanks again.

Yes. I use the same one that I use to synchronize the SU carbs on my British cars.

yep yep but evidently the syncrometer is much better than the unisyn. I won't need mine for a few months. I can sent it up with jamie N. when he comes down next weekend if that timetable works for you

Thanks guys. As you can probably tell, I'm very enthusiastic about doing my own MFI adjustments as part of the larger picture - maintaining the overall tune of our 73E.

Tim, I'm getting a synchrometer on Monday, but thanks for the offer. :)