Went lean...

Guys - I'm confused about what just happened to my AFR. And looking for ideas of what might have happened.

I went and met a guy. He wanted to see my Scamp, and the AVS2 carb. The car ran fine getting there, just cruised only. And a reminder, most don't know or remember. I run an AFR gauge on my car full time, because I'm always tinkering with the tune. LA 360.

So we get there, and during that time I pulled the top off, then pulled the filter and the bottom of the housing off the carb so he could see the carb.

The only thing I can remember is that I fiddled with the breather fitting on the bottom housing. It runs the full closed pcv / breather system. The breather fitting seemed to be sitting in there not quite oriented correctly (from my memory) and noticed the breather filter element was gone.

So I put it all back together and cranked the car and it sat and idled for a while. After a little while I glanced at my AFR gauge and it was idling at about ~20 AFR, versus the ~13.0 or so I normally shoot for.

Then on the ride home, everything was lean. So, what happened? The only thing I can figure is either, the little plastic breather vent thing up inside the filter housing had been sitting at some wrong orientation and negatively affecting airflow into the carb. Or, that when I pulled that stuff off, the breather filter element fell out (why I saw it was missing). But could either of those things (or perhaps both) affect air flow that much???

One last note. I'm running the 1905 AVS2 (with annular boosters). And from day 1 this thing has been a PITA to get tuned. As a matter of fact, I could never get the WOT lean enough. And I have tiny little 0.083" jets in the secondary mains ... and it was still too rich! So it appears that whatever I changed / fixed when I pulled this air filter and housing off has CORRECTED the airflow. Now wide open throttle is a touch leaner than I shoot for. It was ~10.0:1 prior to this (and could never get it leaner, even with 0.083" secondary main jets). But after this event, now it is ~13.5:1.

The problem is not the lean tune. I can easily retune everything. Especially now that I'm getting more air. But ... what could have been the problem? I wasn't suspecting there was a problem. And I wasn't expecting to "fix" anything. I was talking with the guy I met with the whole time, while pulling this filter housing off. So I wasn't looking for problems, not really paying attention. I do remember this breather filter element felt a bit crusty the previous time I messed with it. Could having it fallout out (I didn't see it fall out, but did see it was missing) improve airflow that much? If it were crusty enough, maybe it was not letting the breather breathe much too I guess. Could the vent fitting being misoriented before and fixed after improve airflow that much?

Thanks.


7milesout