[Jeff Higgins]

Thanks, guys. I spent my lunch hour perusing all of the Bosch MFI manuals and parts diagrams over on the tech info page. I can't find any internal adjustments, either. I'll see my buddy again on Saturday (I hope) and grill him a bit more. He is a 935 mechanic (had a couple of cars at Rennsport and Monterey, the white "BP" and the yellow "Road Atlanta" liveried cars). He may be thinking of something unique to 935 pumps.

John, I have the idle A/F all the way down to 14:1; about as lean as this pump will go. The high speed mix goes as lean as 13:1 at 6,000 rpm (as high as I wanted to take my new motor just yet). Off-idle to about 2,800 rpm runs acceptably, in a gradually richening progression from the idle 14:1 to about 12.5:1 at 2,800. Then it takes a real dive into the mid-range fat spot that occurs between 3,000 and 4,000 rpm and goes as rich as 10:1. Once over 4,000, it rapidly recovers to about 12:1 before it begins that typical high rpm progression towards ever leaner. This is at full throttle, mind you, and I'm really not sure there would ever be a reason to "floor it" much below that 4,000 rpm spot. Part throttle in that rev range runs about 11:1; still not great, but better. I have put about 400 miles on it in the last week and honestly cannot detect the rich condition anyway.

Looking at the A/F charts sure gives a graphic representation of where the space cam kicks in and "does its stuff", then when it finally becomes ineffective at 4,000 rpm. I'm kind of guessing here, but the A/F chart seems to show the pump delivery being governed by the low-speed adjustment up to just below 3,000 rpm. The high-speed adjustment seems to kick in about there, with the space cam fighting to keep it initially lean, until the air demands catch up to the "perceived" (by the pump, through its main rack position) fuel demand.

It's quite revealing to see the mix make such rapid changes as various parts of the governing mechanism kick in, and then quit. "Reading between the lines" screams "new space cam"; one that will lean the mid range out more. Which makes sense, considering there is a "T" cam in it now. With the lowest high-speed fuel requirement of the bunch, the "T" space cam probably has the least affect on rack position in the mid-range. I would imagine T, E, and S motors would all have similar part-throttle and full-throttle fuel demands in the mid-range. The S, with its far greater fuel demands at high rpm's, must have the most "aggressive" space cam, to push that main rack further from its richer high rpm setting and down into an acceptable range for a mid-range mix. So, I think that is what I need. My 3.0 liter has even greater high speed fuel requirements, so if I back that high end screw out enough to meet them, the space cam has to deflect the rack further to achive an acceptable mid range. Make sense?

Edit- Dave, I looked at that supplement for the 2.4 pump, along with the drawing of the adjustment bushing. Not quite as simple as turning mixture screws, that's for sure. I would have to have one made, then figure out how to use it. Probably beyond me as well...