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Old December 28th, 2018, 08:19 PM   #4
DannoXYZ
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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
Quote:
Originally Posted by Keithb7 View Post
Last September after removing the airbox snorkel on my stock 2012, I noticed the bike was acting like it was running lean. Harder starting. Poor acceleration from idle. I bought the bike used, it came with 98 main jets and 38 pilot jets. I put up with it as the riding season was wrapping up here. I planned to re-jet the bike this winter.
note that this is a change in behavior. Bike left factory running perfectly, so what changed? Displacement didn't change? Airflow pattern didn't change with full exhaust (slip-ons doesn't really change much), or cam-mods or larger valves.

And higher altitude actually makes mixtures richer due to lower density air.

What you have are clogged carbs that needs complete disassembly, ultrasonic bath in caustic radioactive solvents for weeks, complete flossing of all hidden passages and jets with expanding scrubber wire, along with 10000psi soda blasting. Do search here for "clean carbs ducatiman" for numerous people with same issues.

Don't get cause and effect (symptoms) mixed up. Sure up-sizing jets may cure symptoms temporarily, but you'll need to do it again in couple months. We see it all time, people putting in larger and larger jets to compensate for clogged carbs. But bike still won't run as well as factory-fresh clean condition. It ran perfectly fine when leaving factory, no reason it can't when restored to that conditon.

For reference, most of jetting-DB is for pre-gen bikes. New-gen bikes come from factory with too-rich 11.0:1 or more AFR in high-end with slight leanness in mid-range using 98 jets. My race-bike has all the mods: no snorkel, full exhaust, free-flow intake which results in ~20% more airflow and ~20% more power. But it's still too rich with about 12:1 AFR in high-end. I got dyno-tuned by sponsor Spears Racing and they installed smaller than factory 96 jets to lean out high-end and make even more power. Best power is made around 13.0-13.5:1 AFR and I'm still richer than that.

I suggest you go back to factory jetting with perhaps 1-washer shimmed needles and have your carbs professionally refurbished by ducatiman, you'll be amazed at how much better it runs when restored to factory fresh condition!
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