Reducing mab will have a delay and leaning effect when the mains begin compared to larger mab and then when mains are operating in earnest have an enriching effect adding less air to the mix. Conversely larger mains encourage earlier and richer start of the mains due to the available air to the top emulsion that lifts fuel to the booster. As cfm through the carb increase too much mab can add too much air and trend lean, even worse combined with too much emulsion. Because of the lean trend MJ is usually sized to cover the lean top end exacerbating the earlier and richer start. It’s a see-saw proposition. .025” mab you’ll be holding back start of mains but really help enrichment of WOT (think what that would do to MJ requirements). With .039” mab the mains supplying fuel in the midrange won’t be a problem but will displace fuel in the main well leaning out.
This all has to work with IFR and IAB combination for transition to the mains that does not overlap too much or not at all. Then there is size and amount of emulsion that influences the curve.
With changes suggested do one only at a time. Plug bottom emulsion first. You have the ability to collect data so start with changing the IFR and see what that does to AFR and how far into revs the change is observed, you might find something you like. When thats done don’t change MJ yet and experiment with mab size and it’s effect through the full range. If say a .026” mab has a leaning effect on that 2500-3500rpm range from where it was and becoming richer in the 5500rpm area then drop MJ to regain 5500rpm area AFR and see effect on 2.5-3.5k area. Gone too lean in the lower regions go up to .028” mab and run through the experiment again. I think you will see what I am getting at. When you get close to what you are looking for AFR wise then the IFR may need revisiting but before doing that do a few jumps either way with iab to gauge effect, .065”s and .075”s if starting point is .070”. Going through all that you will be getting a feel of what changes what and how much for more educated guesses of next move. All this might get you to an outcome you are happy with but most guys with an AFR gauge that like tuning will seek finer tuning. This is where emulsion can get you there. Put the bottom e-bleeds back in and observe effect of AFR and how it’s response feels, change top e-bleed size and do same. Always note how the AFR change affects how it feels to drive.
I think I have filled your head with enough now and I look forward to your results when reporting back. Seek advice and information from as many varied sources as you can and align that with what your findings are when experimenting.
Good luck.Statistics: Posted by Right hand drive — Sat Jul 17, 2021 2:45 am
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