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DannoXYZ · July 13th, 2018, 12:35 PM

Here's more related thread with someone installing Ninja 250 carbs on EL250.
https://forums.ninja250.org/posting....&t=78122&tro=1

Tough to diagnose these conditions without instrumentation and datalogging. While you can do trial and error and add fuel to see if it improves. And if it doesn't that means it already has too much fuel and you adjust in opposite direction and it does get better (this was way carb-tuning was done back in '60s).

However, what usually happens is you actually have both lean AND rich conditions at same time. Some areas of operation are lean while others are rich. You can do trial and error and some areas improve while others gets worse. Overall net result is you just move the RPM X throttle-position spot where the stumbling occurs.

The only way I've gotten these things to work cleanly across all RPM ranges and throttle-openings is to do real-time datalogging using wideband O2-sensor recording RPM, throttle-position (via TPS), and AFR in 100-rpm increments. This shows typical low-end lean condition and high-end richness. However due to crude nature of just 3-adjustments, the overlaps aren't smooth making it difficult to add fuel in one spot yet remove it within 1000rpms.

Ultimate solution after graphing and examining all data is to custom-grind my own needles on mini-lathe. Add a concave mid-section instead of linear to richen up mid-range, yet leave the end fat to prevent too much fuel up top. Combined with smaller main-jets and it's finally done!!! Until the temperature or humidity changes and then it's time to pull them again!

All this of course can be done in 5-minutes with several clicks of mouse with EFI.

July 13th, 2018, 12:35 PM	#4
DannoXYZ ninjette.org certified postwhore Name: AKA JacRyann Location: Mesa, AZ Join Date: Dec 2011 Motorcycle(s): CB125T CBR250R-MC19 CBR250RR-MC22 NSR350R-MC21 VF500F CBR600RR SFV650 VFR750F R1M ST1300PA Valkyrie-F6C Posts: A lot. MOTY - 2018, MOTM - Nov '17	Here's more related thread with someone installing Ninja 250 carbs on EL250. https://forums.ninja250.org/posting....&t=78122&tro=1 Tough to diagnose these conditions without instrumentation and datalogging. While you can do trial and error and add fuel to see if it improves. And if it doesn't that means it already has too much fuel and you adjust in opposite direction and it does get better (this was way carb-tuning was done back in '60s). However, what usually happens is you actually have both lean AND rich conditions at same time. Some areas of operation are lean while others are rich. You can do trial and error and some areas improve while others gets worse. Overall net result is you just move the RPM X throttle-position spot where the stumbling occurs. The only way I've gotten these things to work cleanly across all RPM ranges and throttle-openings is to do real-time datalogging using wideband O2-sensor recording RPM, throttle-position (via TPS), and AFR in 100-rpm increments. This shows typical low-end lean condition and high-end richness. However due to crude nature of just 3-adjustments, the overlaps aren't smooth making it difficult to add fuel in one spot yet remove it within 1000rpms. Ultimate solution after graphing and examining all data is to custom-grind my own needles on mini-lathe. Add a concave mid-section instead of linear to richen up mid-range, yet leave the end fat to prevent too much fuel up top. Combined with smaller main-jets and it's finally done!!! Until the temperature or humidity changes and then it's time to pull them again! All this of course can be done in 5-minutes with several clicks of mouse with EFI.