after re-reading "check, measure, adjust", i realized that synchronizing your stacks should be done at 3000 RPM's (of course, after you've correlated all the throttle linkage).

yesterday, i simply synchronized my stacks at idle, not at "part load". so, i'm not surprised that i'm getting more backfires than i was prior to leaning out my stacks.

like i said in my prior post, i went out of order, and really plan to correlate, adjust the micro-switch, then synchronize. after i do it "by the book", i'll report on how the car is running again.

i just purchased a CO meter. after receiving it, and reviewing the "check, measure, adjust" guidelines for the 20th time, i plan to get my correlation right.

then i'll attempt to adjust the different mixture settings using the CO meter as a guide.

And after adjusting those I'll bet you will have no more flat spot....

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'72 911 TE

update on my tune-up project.......

i spent the day finalizing my ignition settings prior to attacking my MFI system. i purchased a CO meter with a good tachometer and reset my dwell to about 39 - 40 degrees @ 950 RPM at 5 degrees ATDC.

i'm glad i purchased the analyzer because i could not get my other tach/dwell meter to act as a tach! i'm sure it was user error, but what the hell !

so with my ignition correct, i got out the "check, measure, adjust" article and went to town. i reset the primary control lever to spec (it was off by 1 mm), and found a few throttle rods to be a little out of adjustment. i also cleaned my air/fuel mixture screws. there was quite a bit of carbon build-up, but nothing a bit of berryman's B-12 couldn't handle. i then reset the mixture screws per spec. 3 1/2 turns from bottom seemed a little rich, but hey, that's what the instruction say.

next, i synch'd my stacks with the flow meter. i took readings at both 1000 and 3000 RPM and all seemed to be in reasonably good order, with a few very minor tweaks. i found that my idle had increased a bit, which seemed a good thing. then i went for a test drive before playing with my CO.

the car ran OK with only a slight hint of the hesitation i had experienced before. i knew i was making progress !

i got back home and played with the idle mixture enrichment instead of the part load adjustment for 2 reasons......#1. it was getting late, and #2. i couldn't figure out where to adjust the part load mixture !

in any event, i kept playing with the idle enrichment screw and re-checking my CO. after many attempts at "rich and check CO", then "lean and check CO", i lost daylight after getting my CO to settle in at approx. 1.5% (a little lean). i took one last test drive and the car is definitely running much better.

next weekend, i'll attempt the part-load CO adjustment (if i can find it !!) then lock in my idle CO.

i definitely know how the MFI system works in unison with other elements of the car. this has been a learning experience. thanks to this website for having so much great materials at my disposal. i couldn't have done this without this site.

TMC: What CO meter did you get. Mind telling me what you paid for it? For everyone else thinking of getting the Permatune Coil: I just got one this weekend and the neck of it is much wider than the stock coil. The stock coil wire rubber cap is too narrow to allow a good connection. I think I am going to have to get some aftermarket coil wire to make it fit.

Kurt V
72 911E

i bought the CO meter from JC whitney. they had 2 for sale, 1 for approx. $169 and 1 for $249. i sprung for the more expensive one. it has a tach and dwell function, too. (i can get the exact model number, if you need it).

it came with a very short plastic hose that connects to the CO analyzer. i purchased a longer hose at the hardware store since i plan to do some part load tests.

so far, i am happy with the product.

looks like i might be on the last few steps toward MFI happiness......during a jury duty assignment today, i brought all the MFI articles just to pass the time. i found the location of the main enrichment adjustment screw (and the 5mm allen nut cover).

when i got home (i wasn't picked to be a juror), i adjusted the main enrichment 2 clicks richer, took a test drive and it was running like a champ. no hesitation, no popping in the stacks.

i got home and put it on the CO tester for grins, and at idle it is about 4% CO, which is a little high. it is idling at approx. 1000 RPM.

i'll fine tune the part load and idle CO %within the proper limits. i'll be watching how my plugs look in the next few weeks, since it seems like i REALLY richened up the entire system.

TMC, you have me confused. You refer to THREE separate mixture adjustments on your MFI: Idle, part load and main enrichment. I only know of two: Idle enrichment which you access thru the fan shroud and the main which is the one behind the 5mm allen head bolt on the MFI. Where is the part load adjustment? Have I been missing something?

Kurt V
72 911E

sorry......main enrichment and part load are one in the same.

"main enrichment" is what the device is called. it is referred as "part load adjustment" in the check/measure/adjust guide. part load means checking CO% either on a dyno or during a road test at approx. 2400 RPM.

Yeah, that main enrichment screw changes things real fast. You have done the whole setup right, and now have the results to prove it. You'll probably find that the engine will run really well within only a click or two either side of where the main enrichment screw is now. One click too lean and the hesitation will show; one too rich and you will smell it- co meter or not!
Road testing with the tools in your pocket will also reap dividends now. You have probably realised by now that going through the procedure you have just been through is the only real way to feel confident about your MFI. It isn't that nasty after all, is it?
I have noticed on this board a reluctance for people to have a go with the MFI unit, and most of the time the problems stem from incorrect adjustment by previous ill informed owners or mechanics. Well the info is right at hand now through pelican, so if you can digest what's there you should be able to tweek it reasonably confidently. What you have to realise is that the settings that you currently have on you MFI pump are by no means gospel: they may just be covering up for lack of knowledgeble setting up in the rest of the system.
For instance, my main pump rod had been set at ONE CENTIMETRE longer than it should have-when the specs say it must be within a fraction of a millimetre of what they quote. Readjusting the rod (after going through absolutely every thing else of course) and resetting the pump mixtures cured 6 months of annoying hesitation and missing for me!
Anyway, glad you seem to have got things sussed. Well done!

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'72 911 TE

One last simple word of wisdom on this topic that helped me enormously...

What is the first thing all of the MFI tuning articles tell you to check? That's right, the air filter. Couldn't be, you say. Well, I finally cured an annoying hesitation that was plaguing me at approximatley 1,800 rpms by throwing my air filter in the front yard one day and going for a ride with open stacks. I was mainly doing it to see how it impacted performance and sound, and inadvertently located a faulty air filter. The funny thing about this one is that the filter was close to new, but it had an oil spot on one side that was interfering with the mixture at that crucial rpm range.

Just a reminder... don't overlook the obvious.

JA

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John
70/73 RS Spec Coupe