Quote:
Originally Posted by 94cobra69ss396
He had a 15:1 AFR at wide open throttle and 10:1 at cruise. He needs to lean out the primaries more to fix the cruise ratio which will make the WOT ratio even leaner. I didn't want him to blow his newly repaired engine. Once he has the WOT ratio to where he wants it it is easy to go back and fine tune the primaries for a good cruise ratio and then readjust the secondaries for a safe WOT ratio again.
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Keep in mind I know only the basic ideas of a carb. I've never worked with one.
So if I understand correctly the principle at work in this context is simply to be safe at WOT and work your way down to cruise.
BASIS
- There are two sets of "jets" which provide fuel to mix with air to the intake
- They are primaries (for idle and low throttle) and secondaries (opening up towards WOT),
which are combined with the primaries
ADAM'S CASE
- He is very rich at idle BUT dangerously lean at WOT.
TUNING SCENARIOS - RON'S POINT (as I understand it)
By enlarging the secondaries first to bring WOT into safe AFR you create a margin of safety. If you reduce the size of the primaries first, even a test towards WOT run could be seriously damaging to the engine.
TUNING SCENARIO - BIRD'S POINT (as I'm totally speculating)
While fine tuning might be subtle, this isn't magic. The observed data that he is rich at idle/low throttle and dangerously lean at WOT suggests smaller jets in the primaries and larger jets in the secondaries. One should be able to make a pretty educated guess based on flow rates of the jets. Then proceed from idle up to WOT progressively in passes. This seems rational to me and I think is what bird might be suggesting.
MY QUESTIONS
If the starting spread in sizes between primaries and secondaries radically differs from experience and theory, it seems to me some other parameter in the "system" is off?
Even if you dial this in for 5lbs boost, aren't you going to completely repeat when you change up to 15lbs (or whatever you're at)? Therefore, if there is a safe progressive method, wouldn't you want to base it on your target max boost?