Making Sense of John Passini's Book

[type26owner]

Whew! Reread the Mainjet section were he generally describes the behavior of a large main and air jets paired together and their mixture pattern going lean at high rpms versus small pairs and discovered I had misinterupted what he stated. He is right on the money actually saying they are opposites. The only source to do so so far that I've found which has confirmed my observations with the AFM exactly. Too bad he didn't have the same tool to work with! Would have really blown my socks off if he'd mentioned two-phase flow but it was not to be.

The only major point he made that I have my doubts about is the accelerator pump circuit contributing lots of fuel at full song. Maybe if the engine revs above 6500 would it then suck hard enough for some fuel to flow through there but below that I got none as far as I can tell. With the standard Lotus jets I had it leaning out to the 20 to 1 range at full song at my 6500 redline. If the accelerator pump circuit is contributing any at all it's only a trickle.

That's why I'm running much smaller jets to get the mixture to 12 to 1 and have it steady through out the whole rpm range.

[type26owner]

Spent the weekend coming up to speed by retuning my car with my AFM so I'm prepared to do same to Sarto's car next weekend at Mike Ostrov's tech day. Realized that the mixture at WOT is adjustable in it's slope only and could adjust it to zero or in other words it stayed the same value independant of rpms. What I could not do is change the mixture range. It's locked into 12:1 and there's nothing that I've done so far to change it. Maybe the float bowl level impacts this or a change of auxiliary venturi size but changing the main and air correctors jets and the choke and the emulsion tubes didn't do squat. Mr Passini why didn't you mention this bit of info?

Got is running sweet! Good thing 12:1 was the target value or I'd be singing the blues.

[type26owner]

Just like to give credit to John Passini for having the correct info in his book afterall. Extracting it was painful and confusing though. If only he had a digital air fuel meter back then I would not have had to do all this work. It still comes down to having a sufficient level of experience though. You'll need to get your hands dirty in the end to be successful at tuning.