Tii mixture screw/idle screw relationship

[Stevenola]

I've read the various posts on how the little screw in the tuna can adjusts idle mixture (lean in, rich out), but if I turn the mix screw out to enrich, the idle drops as the butterfly closes, so in order to raise the idle back up you're supposed to turn in the idle screw on the side of the can, but isn't that just opening back up the butterlfy?  I know it has something to do with the half moon cam but I still don't see how increasing one and decreasing the other back to same rpm affects idle AFR?  I'll hook it to a gas analyzer at some point but I still need to grasp the concept first.

[JsnPpp]

2 minutes ago, Stevenola said:

I've read the various posts on how the little screw in the tuna can adjusts idle mixture (lean in, rich out), but if I turn the mix screw out to enrich, the idle drops as the butterfly closes, so in order to raise the idle back up you're supposed to turn in the idle screw on the side of the can, but isn't that just opening back up the butterlfy?  I know it has something to do with the half moon cam but I still don't see how increasing one and decreasing the other back to same rpm affects idle AFR?  I'll hook it to a gas analyzer at some point but I still need to grasp the concept first.

Steve, I'll shoot you a copy of the A4 tuning manual I wrote that has some discussion of Tii tuning and the relationship of the screws. It may (or may not) help..

 

Jason

[dlacey]

The D Cam shape synchonises the opening of the butterfly with the increase in fuelling by the kugel pump.

The small screw inside the tuna can adjust *just* the air (butterfly) for the given position of the throttle linkage (and therefore the pump fueling is unchanged).

The screw on the outside of the tuna can adjusts *both* fuel and air - it is, in effect, the idle throttle stop but since its pushing on the D cam (inside tunacan) and that cam is mechanically connected to the throttle linkage and the kugel pump, it also sets/adjusts idle fuelling.

 

As you turn the screw on the outside of the tuna can Air & Fuel are altered in unison due to the shape of the D cam...it doesnt adjust AFR..it keeps AFR unchanged as it increases/decreases idle revs. The small screw inside primarily adjusts AFR..and that has a side-effect on revs.

[Mike G]

[Einspritz]

Don't get stressed about the idle CO% it will be what it will be.

 

Tune for smooth idle @ 800-950 rpm or so, and smooth transition to on throttle.

 

First WOT, then partial throttle, then idle

 

 

[gwb72tii]

hope this works.....and helps

tii fuel injection manual.pdf

[Stevenola]

Thanks, I will check all of it out