MFI Part-Load: How Many "Clicks" Per Revolution?

[Jandrews]

I was just reviewing Jeff Higgins' saga when he researched and tuned the white/black screws (in addition to the standard idle and part-load) adjustments. I was also doing some tuning with my LM-1 this weekend, and a thought/recurring question came to me. On the idle adjustment screw, there are clearly six adjustment "clicks" per revolution, as determined by the flats on the hex screw fitted between the sheet metal strips. I couldn't find a close-up photo of the part-load adjustment screw, but the pics in Jeff's thread don't reveal something that would cause a mechanical click similar to what is on the idle circuit. Can anyone post a pic or description of what occurs with a turn of the part-load screw?

Thanks,

JA

[Jandrews]

Anyone have any information on the "clicks" for the Part-load screw?


JA

[Zeke]

Can you link the thread about the black/white screws? That's a new one for me.

[philippeF]

you mean the main rack ?

[Jandrews]

Milt...here is the link to the Higgins thread:

MFI Pump - Open Heart Surgery

And philippeF, yes, the main rack is the adjustment that my question pertains to.

Thanks,

JA

[356RS]

The Main rack adjusting screw has 12 clicks per one full turn. The governor head spring screws have 6 clicks for one full turn. The same is true for all the spring screws on the spring adjusting head. Black screws (2) are mid range" 950 RPM to about 2000 RPM" and the (2) white screws are high end screws " 2000 RPM on up.



The larger of the two springs is the mid range spring

[356RS]

This is the main rack screw.

[Jandrews]

Mark...I have been following every word of your MFI dyno build! Incredible information and I know many (including me) are very appreciative for it.

I recall from other sources/discussions, and observed from my own experience that the main rack screw does indeed appear to have 12 clicks. What I am asking is, what determines the "clicks"? It is easy to see what determines the 6 clicks for the governer, but even from your photos, I can't tell what action that screw takes on the rack, and what determines an actual "click" for the screw.

Does that make sense?

Thanks,

JA

[356RS]

This may help. As you turn the screw clockwise you are pulling the main rack toward you and that is causing all six of the plungers to turn toward a leaner position in there cylinders. Of course turning Counter Clockwise will push the rack away from you and into a richer mixture for all six plungers.
Two clicks will make a 1ml change on the flow test for 1/2 throttle @ 2000 RPM.

[Jandrews]

Wow! Thank you, Mark! That is EXACTLY what I was looking for. And to know further that two clicks equals 1ml at 2K is amazing! Any way to show/describe what those 12 geared teeth engage to perform the "click"/adjustment? Edit: I assume it rides that pin on the spring?

Now, from your dyno work, any idea how much of a difference 1 ml makes in real world performance?

A quick story: My car (2.4S MFI motor - now 2.7RS) runs fantastic!! Good, smooth performance at all RPM's levels, GREAT power all the way to 7,300...it just screams. Pump was rebuilt and recalibrated by Gus a few years ago, and I have tinkered with the adjustments periodically while keeping track of all changes. I recently picked up an LM-1, mostly for fun, but also because I was suspicious that both idle and main rack were quite rich. Gas mileage isn't great, sometimes a fuel smell, tailpipe is black, and oil gets dark fairly quickly (completely rebuilt motor).

LM-1 runs seems to confirm my suspicions. I have the charts (and will try to post them when I get home), but basically idle is around 11:1 and at 7K it is around 12.3:1. After a few repeatable runs like that, I brought my adjustment tools and tried to go a little leaner. Three clicks leaner on main rack and two clicks leaner on idle seemed to have no effect on the LM-1...basically the same numbers. My seat of the pants meter seemed to suggest that leaning it out SLIGHTLY decreased power. Could be just hallucinating, though. Then, when I got back home, I adjusted back to the original positions for main and idle, since it just runs so darn strong there.

When adjusting the main and idle back, it occurred to me how "rough" the adjustment clicks feel. I drew an arrow on the end of my adjustment tools with a permanent marker to represent clock positions. This helps immensely in keeping track of where you have been with adjustments. For example, I know 11:00 is where my main rack seems to run best. With the arrow, I can always get back there. However, sometimes, with both the idle and the main rack, it feels like you turned the screw but you can't be sure. Anyway, rambling a bit here, but I think you get the point.

In your experience, would 1 click on the main rack show up on the LM-1? How about 2 clicks? How about on the idle screw?

Thanks!!

JA

[356RS]

First: That pump Gus did shouldn't need any adjustments. He is the Master. Maybe a little adjustment to the idle to suit your needs.
Second: It is so important to make sure the CMA have been gone through. 99% of the time your MFI problems can be found following the CMA.
You said your exhaust pipe is black and engine seems to be running rich. Have you checked your warm up thermostat hoses?
As far as how many clicks on the main will show on your LM-1 meter, 2 clicks with the car under a good load will give me a change on my meter. Hope this helps you out.

[Jandrews]

Thanks Mark. I have been all the way through CMA, in order, with rigor. MFI thermostat hoses are in new/excellent condition. Any thoughts on how rich 12.3:1 is for main rack under load? 11:1 for idle? Too rich?

Thanks,

JA

[philippeF]

12.3 at 7k is good
you may notice a difference with 2 clicks on the main rack
none on the iddle ....
Mark's demonstration is impressing ...
i have a 2.7RS engine too, it likes to be in the 12-13 afr area ....

[356RS]

Philippe is right John. They like it a little rich. 12.3 sounds fine to me. (it rhymes) I wouldn't let it get any lower than that under load. Warm it up and have some fun.