I am trying to figure out the theory for syncing and timing a bike (MV
Agusta F4) with Marelli IAW16M ECU (the one with the big plug for EPROM
change and fuel trim trimpot.) I have the workshop manual and the engine
manual, but they are internally inconsistent and contradictory.
As I see it, there are 2 separate objectives - balance and mixture.
The air bleed screw seems to affect both balance and mixture. since it adds
more or less air for the same throttle position sensed.
The throttle linkage adjustments do the same, since there is only one TPS.
My bike only has one CO spigot on the pipes, so there is no way (that I know
of) to read CO of a particular cylinder.
So it seems like you could have 1 cyl relatively rich and another one
relatively lean, and the reading might average out and look OK.
Is this where sync comes in? I suppose the theory is to tune for equal
vacuum 1st, then adjust CO and assume that equal vacuum=equal mixture.
On my bike, cyl 1 pulls more vacuum at 2000-3000RPM than 2-3-4 do, even
after balancing vacuum at idle. If I try to compensate by opening the bleed
screw, it seems like I risk leaning out that cylinder (more air, less gas)
So I suppose I need to figure out why that cylinder pulls more vacuum. I
suppose the intake valve might need a shorter shim. if it were shimmed too
much, I suppose that might yield more intake duration and thus more vacuum?
I understand how to do all the adjustments at idle, but not how to know if
things are OK at higher RPM, where it really matters. My understanding id
the ECU diagnostic software (which I don't have) can adjust fuel trim as
a percentage, vs. the fixed time adder of the trimpot.
Any wisdom would be welcome. There are no dealers in my area, so this is
going to have to be DIY. I have a gastester and a mercury manometer.
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