How to sync & Tune Marelli FI Bike?

I am trying to figure out the theory for syncing and tining a mike (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 inconsistant 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 particilar cylinder.

So it seems liek 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 unserstand 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 inderstanding id
the 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 wisdome would be welcome. There are no dealers in my ares, so this is
going to have to be DIY. I have a gastester and a mercury manometer.

 

I'm surprised the MV Agusta doesn't have a plug on each exhaust header.
Without that, there is no way I know of to balance the CO perfectly.

Here's what I would do:

You will need a method to read the TPS adjustment. I believe Technoresearch
makes a Palm based device that will work on your bike.

Back off the idle stop screw all the way. Adjust the throttle body linkage
very carefully so both throttle plates snap shut simultaneously. Test your
adjustment by putting a bit of pressure on the throttle grip (as if you are
trying to almost crack the throttle off idle) and tap on each plate to make
sure it takes the same pressure to hear it tap shut. Adjust the TPS to 0
degrees, making sure the throttle plates are fully closed by tapping on
them.

Turn both air adjustment screws all the way closed. Turn the idle adjust
screw until the throttle plates are cracked open enough to start and adjust
the idle screw again to get a comfortable idle. Now, use your manometer to
check the vacuum balance at around 2500-3000 rpms. It would be better if
this step could be done under slight load on a dynometer but if you don't
have access, don't worry. Open one air bleed until you have perfect balance.
Check vacuum balance at idle to make sure it is close. If your valves were
well adjusted and the engine is in good condition it should be close. If
it's not, then you have a problem.

Now check your CO mixture at idle. Use the fuel trim pot to get it where you
want it. You may have to adjust the idle screw slightly to maintain proper
idle speed.

Using this method you will not be balancing the fuel mix between the
cylinders but that's all you can do short of installing another CO plug if
there really is only one CO plug in the headers. However, if everything
balances out reasonably well without needing to open the air bleed
excessively, your CO balance should be close enough.

Spanky

 

Thanks for the very helpful suggestions. The MV is a 4 cyl, and the problem
I'm having is that Cyl 1has higher vacuum at 3K than 2-4, but lower vacuum
at 1k rpm. I'm thinking the balance is more important at higher RPM than at
lower, since the engine spends more time there and is under load there more
often.

I'm not sure the air bleeds have enough effect at 3K to correct, but I
haven't tried yet (still trying to find longer thickwall tubing the the
motion-pro cheapie manometer.)

I'll probably have to bite the bullet and have the valves adjusted. I was
hoping a simple sync would do it, but it's not looking that way. Seems like
valve adjustment could reduce vacuum but not raise it, since thinker shims
would lose sealing and thinner shims would reduce duration. So in order for
that to be the explanation here, cylinders 2-4 would have to be wrong, and 1
better. Seems strange.

Dave