The Mighty DR650

Contributors: Early Access BETA: Plan Your Build
#21

Quick update on this fueling saga.
I think i got some condensation on the LSU4.9 sensor :(. It was cold and i went and cranked the bike up and the sensor went to full lean.

However, just day before, i finished some tuning with a new set of parts from Factory Pro. Put in their softer spring, a 45 pilot (up from 42.5) and reset the idle and idle mixture(1 full turn).
With this kit the bike feels good, though the fuel mix is considerably more rich.
AFRs:
Low speed cruise <40 - upper 12s
High speed cruise >40 - depending on gear 13s-low 15s
Idle - Low 12s
Lugging full throttle - high 10s
WOT >2k RPM - mid 13s.

Overall, you can only get a dead spot if you’re cruising at 1/4-1/3 throttle and snap to full open, it’ll lean past 17.5 for a single reading and then richen up.

I’ve got a spare sensor on hand and i retained all the original carburetor parts, so once i can get my hands on a nano kit i’ll be able to provide input on the factory tune (which is purported to be fantastic gas mileage, in the range of 60mpg) and the factory pro kit, and nano should be able to reproduce them reasonably well without the unnecessary excessive lean-ness on fast throttle change.

#22

I’ve noticed when i have a carb boot leak, I get this like squeak chirp noise at low rpm. and studdering.

CV carbs are kind of a slug on quick throttle changes. The vacuum diaphragms can only respond so quickly so no matter how “fast” you want that snap, it will never be like a flat slide.
Computer controlled carbs are… Emissions. Flat out. A tm40 pumper carb on a big thumper will snap like a 2t and can easily control even the most turbulent intakes. The intake velocities alone are brililant. my buddy put a set of TM34-86 pumpers custom setup by topham mikuni for the XS650 engine and it went from sluggish to chirping the tire if he snapped to hard.
The computer controlled secondaries act like vacuum secondaries on a car, except now you have to meet certain “requirements” before you get to utilize all of the available CFM. Its maddening.

Those O2 sensors are the unheated type. The 4 wire bosch wideband sensors have an internal heater to prevent corrosion and false readings while in open loop mode. Also most O2 sensors need few moments to normalize in the exhaust gasses before it can even give a good reading.