That doesn't make any sense to me.

Adam, look for an e-mail from me.

Unless it's an ode to Adam's biceps, post it here so I can learn something. As for not understanding, the apparent contradictions will get hashed out.

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.

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? :huh:

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?

That's how I do it.

Bad Data
 

This isn't a carb thing. Adam, if you've been blasting around much with a bad tune that varies from super rich and especially to dangerously lean for any extended period of time, you may have seriously compromised your O2 sensor. This is really possible if you've ever had serious detonation or back-firing. Further tuning may be in the dark.

Makes sense. The only caveat as I can imagine is that if you dial in a great AFR for WOT and you're rich at idle, then reduce your primaries, you're going to be lean at WOT and the cycle continues. I understand, in purely conceptual terms, the idea of calculating a starting point, and very progressively running up through throttle positions off idle.

The ratio at idle is adjusted differently than the cruise ratio. He will adjust the idle mixture with the idle mixture screws. As for the primaries they have an affect on both cruise and WOT. The only reason I suggested that he adjust the WOT first is because he already broke one piston from it. No need to do it again. I'm not a carb expert and can only tell you from adjusting my own carb on the Chevelle. I've never tuned a my carb using an A/F meter but I did have the Chevelle dyno tested once after I built the 454 just to make sure I was close and the AFR was 12.6-12.8 from 3000 to 6500. This was after tuning it at the track and cruising it around town to fine tune the drivability.

No. Did you only read my first post? As of today I'm at 12:1 under boost. See graph. Assuming I don't run out of fuel it should stay around 12:1 at 10 lbs, carb meters air to fuel. Once you get the AFR right a good carb should keep it steady, at least at that throttle position.

The primaries are supposed to be about 10 sizes lower than the secondaries, because the PV on the primary side compensates about that much. With no PV, you should run equal size jets.

Going to screw with the PCVRs to get the boosted AFR a lil richer, then I'll tune down the primaries, and depending on the response I get after f'n with my PCVRs I might even jet down the secondaries.



As far as the O2 sensor, I just installed it the other day. It's brand new, and per mfr spec, I will only leave it in when tuning.

Yes. I read your first post.

Did I misunderstand it in principle? Light Throttle = rich, Heavy Throttle = Lean

It's a spectrum of rich -> lean according to throttle position???

Define PV.

Define PCVR.


It only takes ONE lean backfire to destroy an O2's ability to accurately represent the amount of oxygen flowing by. To my understanding.