MFI idle rack adjustment

[obrut]

Is it possible to adjust this rack too far and have it disconnect? Adjusting the idle rack on my car makes zero difference to the engine (on a chassis dyno) at all.

I haven't opened up the pump but assume there is a threaded rod going into a threaded hole somewhere.

The guy who dyno'd my rally car thinks this has occurred (and is very good with MFI) but I thought I would double check here also.

Is the fix as simple as getting the rod to engage the hole again? How much disassembly is needed. (I have a spare pump to practise on)

[304065]

Ryan,

Look at the "MFI open heart surgery thread" for detailed pics of the internal adjusting screw. Yes, it is possible to back the screw out too far and bugger the works.

Why do you say adjusting the idle rack makes no difference? Following CMA, you would adjust the part-load setting FIRST and then finish things with the idle.

[obrut]

john

thanks - i'll look up the thread you mention.

we couldn't follow CMA given the problem. my tuner got the motor as good as he could (which was very good 270+ hp out of 2.8 litres) but with some low end flat spots as the top end tune compromised the bottom end tune - which couldn't be initially sorted with the idle rack.

any ideas on how hard/simple it is to reconnect the idle rack?

[obrut]

ps. john - is the surgery thread here or on the main board. my searches haven't located it yet.

[jcge]

MFI open heart surgery

Are you talking about the RACK HEAD (2) or the IDLE SCREW (15) ?

If you have a spare pump, just open the rear cover and you will see how they connect to their respective counterparts - no adjustments are effected by removing the cover (6 screws). Should be a simple reconnection.

If you do open the pump whilst mounted on the engine, be prepared to catch a fair amount of oil as the oil overflow return to engine is located on the pump side cover plate (upper fitting). It's full of oil to about the centreline of the drive shaft (pump cam).

Alternatvely you can try and syringe the oil out as Jeff describes in the open heart thread.

[obrut]

jcge - thanks. rack head adjustment is working, but idel screw appears not.

i will investigate with the spare pump (which is connected correctly as i can feel the idle screw adjuster 'lock' into the idle screw when depressed).

(and thanks for the oil tip!)

[pjh69911]

What is your idle speed? If too high(say over 1000) then the idle screw won't have any significant effect as the much stiffer midrange spring's force will overshadow any change in the small idle spring.

[356RS]

Ryan, Don't mean to hijack your thread, but wanted to see if Paul has an answer to the high idle speed/idle speed screw spring in the pump. Can the spring be altered?

[pjh69911]

Mark,
The spring rate is designed to be in the ballpark of the centrifugal force applied by the centrifugal weights at a particuliar speed range. At idle, the force is small and hence a small spring can provide a comparable force against the centrifugal weights. If the spring were alot stiffer, then at idle the weights would not change their position in response to idle spring adjustments, and no change in A/F ratio would be achieved. That said, if you were too lean at idle, and ran out of adjustment, you might be able to stretch the spring length a bit and richen the idle mixture. You better have a spare spring though, and it wouldn't be my first move. Paul.

[obrut]

idle speed is about 800/900 rpm

[BURN-BROS]

Ryan,

#15 may have damaged threads. I have come across this failure more than once!

[356RS]

Thanks Paul, I understand.