MFI main enrichment help

[cmcfaul]

I can't seem to get the main MFI mixture adjustment to engage with the screw driver I modified to add a couple clicks of enrichment.

Following is the tool I made. I adjusted the idle richment, no problem.

I removed the 5mm alen bolt and can insert the screwdriver about 1.5 inches into the pump but can't get the screw driver to engage the internal screw. I want to add 2 or 3 clicks of enrichment. Them LM1 says I am at 15 at WOT.

Does the screw driver have to be at a slight angle. could I be past the screw? Is my tool flawed?

Any advice is greatly appreciated.

Chris
73 911 E

[edmayo]

I can't tell from the picture what tip size you have on the screwdriver, but it is a fairly small tip. I'll measure one tomorrow and get you the exact width and thickness. I'll also get the exact length, if that red tape is a splice that whole deal is longer than necessary. The alignment is straight in, no angle needed.

[2.5MFI]

The screwdriver blade should have a 1/8" tip to fit correctly. As Ed said, straight in, no angle. Counter clockwise to richen it up.

[2.5MFI]

Just a thought but how are your A/F measurements at mid range and idle? If they are good then you are going to richen them up also by adjusting the main rack.

[Alan.uk]

In case a pic helps, you can see the main rack adjustment screw here. In this pic we have removed and space cam and govener.



HTH

Alan

[edmayo]

The width of the screwdriver tip is an 1/8th". The length of the blade is 14". As you can see the screwdriver is inserted past the coil which will align it straight into the pump. Hope this clears it up for you, along with Alan's picture of the adjuster itself, and Mark's explanation of direction.

[cmcfaul]

GREAT replies! Exactly the pics and info I was looking for. I can feel the tool hitting a spring type object when I turn it. If I push it slightly it will flex in very slightly (spongy feeling). I am going in exactly the same as the pic and moved everything out of the way, so it is almost perfectly straight. Think I am going to make a more flexible tool.

Current tool blade end is 4 mm wide

I am 17 at idle, 13.5 at part throttle and 15 at WOT.

I added two clicks of idle richment and have not measured since. Part throttle is perfect but WOT is lean. Wish I could just add richment to WOT.

Chris
73 911 E

[edmayo]

Just so we're all straight on this, there are two adjusters, the rack adjustment will affect the entire range. It is the adjustment I've shown with the screwdriver tool. On this adjuster CCW is richer. The other adjustment is idle, and it is done with the spring loaded adjuster further down on the face of the pump. That tool (not shown) uses a 8mm socket end, and is done by inserting the tool through the fan blade and an appropriate hole in the fan housing. Pushing against the spring and turning will engage the adjustment tang, richer on that adjuster is CW. The usual procedure is to get the load (rack) adjustment done first since that affects the entire range. After that is done the final step is to adjust the idle adjustment since that ONLY affects idle. The idle circuit carries up through ABOUT 2500-3,000 RPM at which point the load circuit will start having a greater influence. It appears you will have to next get an idle adjustment tool to bring your idle mixture up which is now way too lean. It should be about 12.5-to 13.5 at idle depending on what your particular engine runs best at. Of course all this assumes that you have done all the preliminary work such as pump rod length adjustment, ensuring that all the individual throttle rods are set right (so throttle plates aren't open at idle), points and timing correct, pump timing correct, and cam timing correct.

[Flieger]

A richer-than-peak-power idle means better throttle response since when the throttle butterflies open, they allow more air in, which makes the mixture leaner into the peak power range, and gives more power for acceleration.

[cmcfaul]

I am giving up for now. Cut my tool down so it goes in perfectly streight, still won't engage the screw. I think I am below and past it. I am going to add a turn of linkage and that should give me more enrichment for now accross the whole range.

It runs perfectly as is though a bit hard starting when cold. Because of the cam I am using it might be better suited for the S space cam. Will look into that a bit more once it warms up outside.

Chris
73 911 E