MFI idle mixture adjust

[POKDUB]

Quick question.

I know that on the main mixture adjustment there is a definite click as one turns the adjustment, however should the the idle mixture adjustment also be a click, or is it just a linear turn.

When I push in the idle mixture adjustment, and turn slightly, I can feel the mechanism tooth engage for adjusting, however when I turn it there is no definite click, is this correct ?

[Rot 911]

In my experience on my '72E I never felt a click. Engagement yes, but no click.

[304065]

Peter,

I just did this on Friday. It's not an audible "click" like the main rack, it's more of a "detent" kind of feeling. You push in on the spring-loaded screw and turn (remember "I Lean Left") and the screw moves a definite amount before it kind of pops back into the next detent.

Hope that helps.

[POKDUB]

John, Kurt,

Tks for experiences. I can feel the adjust engage, just like turning a flat head screwdriver on top of a screw until it pops into the groove.

Does this adjustment bottom out ?

I am trying to lean off the idle mixture, however it seems to allow any number of turns, ie never reaches a fully screwed in position.

[Rot 911]

Peter you really need some way to measure the exhaust gas. I used a fairly inexpensive Gunson tester. Here is a review I wrote up back in 2001:

Product Review: Gunson Gas Tester

On August 14, based on comments from other member of this board and the British car board I am on, I ordered the Gunson Gas Tester to assist me in my MFI tuning woes. Ordered it online from Auto Expert Products http://www.aep.bigstep.com/catalog.html and it was delivered to my doorstep on August 19 for $137.00. I had previously described my problems with my MFI as "the car runs great when you first start it up, then while it warms to 180 it progressively runs worse (back firing upon decelleration etc). However, on my 72 911E once the temp gets up to the 180-190 range the backfiring in the exhaust on decelleration and popping during accelleration in the 1000-2000 rpm range lessen, but never completely go away." John Walker suggests that the MFI needs to be set much richer than the factory recommneds (approximately 3% for idle and main settings). He states:"the CO at idle and at 3000RPM usually has to be around 5%-6% and 7%-8% respectively to get decent transition. the factory settings were really lean. how they got them to run right is beyond me."

Well I took my tester home and followed the very easy instructions. I was convinced that my idle setting was probably too lean (probably around 5%) and the main enrichment (also know as "part idle") setting was close to being spot on (in the 7-8% range). Shows what I know. Turns out both settings were right around 4.3%. Way too lean. It was now actually fun to adjust the screws and see how the mixture was affected. I stopped when I had the idle set at 4.9% and the main at 7% to see how the engine would respond when cold. This morning hopped in and drove to work. While all the problems are not completely resolved, the engine no longer has ANY backfiring thru the exhaust and the popping during accelleration during warm up in the 1000-2500rpm range has decreased dramatically (I would say 90% reduced). The car is actually driveable around town! I am going to try to get both settings in the middle of John's recommended range and see if that completely fixes the problems. Bottom line, I think the tester is well worth the money I paid. If for no other reason in that it told me the adjustments on my MFI work and that I don't need to spend big bucks to have it rebuilt. Second, no more hit and miss on the adjustments. I can quickly see what the results are. I believe the tester to be sufficiently accurate to get the proper fuel mixture settings. Finally, Wayne, why aren't you selling these? In areas where they have emissions testing it would appear this tester would be a steady seller. As far as I can tell only JC Whitney and Auto Expert Products carry the tester.

[POKDUB]

Kurt,

I think my brother-in-law has one which I can borrow.

Tks.