Tuning stock L-jet

[Westy78]

I'm trying to get my AFR dialed in on my '78 Bus with stock L-jet. This is a bone stock 2.0 with around 80k miles and no known vacuum leaks, fuel pressure within spec and rebuilt injectors. Last compression test had all cylinders at 120-125psi. This same FI is going to be going on my Camper Special so I want to get it as close as I can before making the switch to the new engine.

Using an LM-1 I got the AFR to 12.8:1-13.0:1 at WOT up hill in third doing 40mph. I think this is very close to where I want to be but at highway cruise or light throttle cruise and at idle it leans out to very near stoich, 14.5-15.0:1. This runs the head temp up to high (380°-400° using a Dakota Digital gauge). Double checked the timing and it is at 28° at 3500rpm with advance hose disconnected. It falls back to 8° at an idle of ~1000. This is using a stock 205P distributor. With vacuum hose connected it advances to ~34° at 3500rpm.

I've adjusted the black wheel in the AFM to get to the WOT readings. Also a very small adjustment counter clock wise on the AFM potentiometer using the small screw. As I understand the AFM, the black cog or wheel adjusts the "MAP" of the mixture and the small screw adjustment changes the MAP up and down the rpm range? Is that correct or totally wrong? What adjustment should I make to bring the cruise AFR into line? Or is stoich what I want at cruise and my high head temps are caused by another issue? All of these readings were taken with ambient air temps of ~75°.

Any suggestions?

[vwlover77]

So, if I'm interpreting this right, you need to enrich the light-throttle cruise mixture, while maintaining the WOT mixture.

I'm no expert, but my suggestion would be that you need to loosen the tension of the cog wheel spring to allow the potentiometer to swing farther to the left under light throttle conditions. This is done by moving the cog wheel counter-clockwise, iirc....

My guess is that the WOT mixture will change only slightly as a result of this.

I would focus on adjusting the mixture at cruise rather than WOT. Adjust correctly for cruise, and WOT should take care of itself.

[Bleyseng]

at partload (cruise) 14.0to1 to 14.5 to 1 is where you should be. WOT should take care of itself but check it underload.

adjusting the AFR will affect the CHT's some but is not a cureall.

[Amskeptic]

At full throttle, the AFM is no longer moderating the fuel delivery signal. The wiper is buried all the way to the left. The ECU is responsible for WOT mixture. At this point, the only variables affecting the WOT mixture are temp sensors, fuel pressure, injector cleanliness, and amount of bypass air flowing through the AFM's mixture screw circuit.

The black cog affects the slope of the fuel delivery map. Do not screw with this thing trying to change WOT fuel ratio. It should only be adjusted in strict concert with wiper adjustment, and these adjustments are to be figured out only after you have answered idle mixture? and 3,000 rpm mixture? That is the only way you can sucessfully solve the matrix of rich/lean-low rpm/high rpm.

I have found, honest-to-god, that asking the engine directly what it wants is vastly superior to asking test equipment what it thinks the engine wants.
Colin