Hello folks, how I've never found this forum before is beyond me but here I am and hello.
I am hoping you may be able to offer some pearls of wisdom regarding my kjetronic/cis injection system. I appreciate I am not a regular in here and that this may be taken as me taking the mick, so really appreciate any guidance.
Many years ago I substantially altered the air flow characteristics of my ford v6 engine, fast road cam, gas flowed big valve head, raised compression, port matched and flowed everything and self build full exhaust system. The results were staggering on the road and a dyno session confirmed I had gained significant power, but! The car ran lean at all but high rpm wot and idle.
The system is kjetronic basic no lambda. When I first fitted all the mods I recall having to lean off the idle 3/4 of a turn in order to get it to run. Fast forward 2 kids, a house etc and countless hours of roadside fuel adjustments aided by a wide band lambda I have a pretty good fuel curve, great economy with only one flat spot due to a rich situation at 4500 rpm. What I have done is reduce both control pressure with vacuum and without until my car runs nicely between 14 and 16.5 lambda at light load an cruise situations, at wot a lovely 12.5 to 13 afr is achieved until 4000 rpm where it starts to drop until rich misfire short of full speed at 6000rpm. I have added a limit screw to stop the afm arm at a position that supplies perfect afr at 6000rpm which means at 4500 rpm the afr is 10.8 and a slight dip in pull can be felt from the drivers seat as you pass through this rpm. The idle afr runs between 12.5 and 13 and is set to produce the highest stable vacuum of 16 inches of mercury, the idle is a bit weak and the idle speed bypass on the throttle has limited control over the speed ie I struggle to get a fast enough idle, running plenum vacuum to the distributor advance has meant I once again can adjust the idle and run it fast at 1000rpm because if is a little prone to stalling under electrical load.
Now you have some background I'll ask my question. I have read this amazing forum for several days and searched all sorts of amazing posts and many of which people suggest resetting the idle position of the metering arm by reducing the fulcrum counter weight. This fascinates me and I think may hold the key to my fuel curve. My afm bowl has a very shallow curve that gets steeper in the last 1/4 of the bowl, I suspect that as I think is suggested in several posts that I need to get my arm lower at idle to keep away from this upper angle change as I think it's what may be causing my engine to richen up at high rpm. When I first fired up my "new" engine I had to lean the mixture substantially in order to get it to run, I interpret this as the arm raising higher in the cone than it did with the standard engine for the idle air flow. If I can get it lower at idle I will likely need a little more control pressure and in turn keep the arm lower in the cone at high rpm.
That's my theory, basically that reducing the fulcrum balance weight and resetting everything during road use over time and maybe removing or reintroducing weight to the balance as needed could raise the rich area in my fuel curve above maximum rpm. I plan to drill and tap blind holes in the weight and use grub screws to reintroduce and fine tune weight as required.
Do you have any pearls or input? Or even tell me if I'm flogging a dead horse by all means and that what I have is as good as it will get.
Regards Jon