I took a bit of of a break from carb optimizing to swap out my exhaust (removed B&B 1.75" system / replaced with SSI's (1.5") and Dansk 2 to 1 muffler). Back on the carbs this weekend...
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F16 to F8 Emulsion Tube Swap
I replaced my F16 emulsion tubes with F8's this weekend. I wanted to try the F8's see if they activated my main circuit at lower RPM's; which would then allow me to lean out my rich idle/progression circuit a bit more.
Well, the F8's definitely enriched the mixture at low to mid RPM's - and how
The engine went rich to the point of bogging as the AFR's continued to drop into the 9 range.
Theory in Practice: The F16 e-tube diameter is 8.2mm vs the F8 at 7.5mm. As such, since the F8 is smaller, it allows more fuel to fill / reside in the well that the main jet/e-tube assembly sits in. This reservoir of fuel is immediately available to draw upon as the main circuit begins to activate and contribute - which turned out to be too much fuel at that RPM range for my engine config. The F8 essentially produces results similar to a prolonged squirt from the acceleration pump.
Bottom line - the F8 doesn't appear to be optimal for my engine config. I think the F8's are probably best suited for a larger displacement engine (3.6 - 3.8L?), or a config that really demands a lot of fuel at low to mid RPM ranges.
Good hands on learning point... If I swap tubes in the future, I think I will stick to something in an 8 to 8.2mm diameter range.
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Idle Air Corrector Sizing
I'm running 55 idle jets - which have tended to be quite rich for most driving conditions.
A few weeks ago, I reamed out the PMO idle air correctors - opening them from the original 1.20 size to 1.40. This really helped with my rich idle/progression issue - taking me from ~ mid 10's to mid 11 AFR readings during low to mid RPM driving and cruise conditions.
This week, I opened the idle air correctors up a bit more to 1.50. I think this size is going to be about as good as it gets. With the 55 idle jets and 1.50 idle air correctors, my low to mid RPM driving and cruise seems to settle out in the mid 12 AFR range with a few momentary drops to the mid-10's and momentary spikes to the mid-14's.
I'm getting a little popping here and there (third gear drives down twisting roads) - but the engine is responsive and strong. I think with a little more time spent getting a good mixture adjustment, it will work out just fine.
I'm want to replace my reamed PMO idle air correctors with a manufactured set of 1.50's. The Solex main jets with M6 threads appear to be exactly the same as the stainless steel idle air corrector jets that are originally installed in the PMO's (I will call Richard to confirm):
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Leaning out the Main Circuit with Smaller Main Jets
Last week, I ran my F16 e-tubes with 170 mains and 190 air correctors and found that I was too rich as the main circuit came in at low to mid-RPM's.
This week I took a set of 180 main jets, soldered them shut and reamed them out to ~ 140's and paired them with some 180 air correctors (to richen at higher RPM, smallest I had on hand).
The 140 main jets seem to be about optimal for my engine configuration (smaller than I would have expected).
Here's my normal hill climb driving profile:
The 140 mains seem to be just right - hitting mid 12 AFR's, but climbing to the mid 14's by 6,000 RPM. I'm reasonably confident I can remedy this with smaller air correctors, which should also help the main circuit come on earlier / in the lower RPM range which will help mitigate the idle circuit leaning out at ~ 2,700 RPM.
I'm not too worried about the mid-RPM idle circuit leaning (14.95 AFR before the mains jump in). Although the hill profile is a great driving profile to isolate and adjust your idle and main circuits, it's not representative of normal driving...
Additionally - I didn't notice any idle to main circuit transition hesitation with this combination (neither from a slow throttle advance or stomping to wide open throttle) - which is nice...
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All set for a quick drive tomorrow AM to check out some smaller main air controller jets (soldered and reamed a set of 190's - resized to 140's to start).
It's been a productive weekend - I'm getting very close to what I would consider
optimal.
Gordo