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Old 06-17-2009, 02:32 PM   #19 (permalink)
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B2300 - '96 Mazda B2300 SE

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Originally Posted by theycallmeebryan View Post
I think its possible for me to reach 100mpg too... i am very close

My carbs are much smaller. The stock float bowl height in my carbs is 17mm, and when i took the carbs out a few months ago to clean them, they were both exactly at 17mm. I dont think i'll be able to decrease it nearly as much as you did. I may only be able to go 3-5mm.

I dont think i ever use the main jets on my bike. In fact, most of my riding probably is influenced by the pilot jet and screw. Even on the highway, i dont think i go more than half throttle, even with the changed gearing.

Are you suggesting using a narrow band or wide band sensor? I have a few narrow band sensors laying around from various cars i have owned. The only wideband i have is in my 1984 Buick Grand National, and its a part of the FAST standalone ecu that i have in the car. All a narrow band + voltmeter will tell me though is whether or not my current mixture is stoichiometric. I can see your pint. The only problem is that the exhaust pipes on the ninja 250 are only 3/4" ID each (i just measured), so i would need to find a NB sensor small enough to fit.

Another thing is that in stock configuration, the Carbs on this bike are a hassle to work on.... because of the huge factory air box. If i were to replace the airbox with pods, it would make things much easier.
I was suggesting using the NB sensor so you'd know if it was rich or lean. Using it over varying conditions would give you a general idea where it was rich or lean. Since you already have a WB sensor in the GN you could temporarily use that and have a really good idea of how far you need to adjust the mixture. I seem to recall that about 15.3:1 is about it for maximum fuel efficiency but that is probably for an OHV v8 IIRC. Some aircraft owners go up to 22:1 (and higher) at WOT lean cruise. The 250 has little tiny combustion chambers and a very short flame distance so you may be able to go really lean. A good subject for an experiment.

Because the pipes are small, stand-off the sensor from the exhaust flow so like only half of it is directly in the exhaust flow. It may slow the response of the sensor some but your brain isn't processing at the speed of your cars computer anyway so it won't matter.

You probably already know this, but the sensor needs to be close enough to the head to heat up to 600-800 degrees F to work properly. If you get a heated 4 wire sensor you can put it in another possibly more convenient location.

I'd guess, and it's only a guess, you are solidly in the needle intermediate circuit due to load. The pilot and idle circuits also contribute but the idle less so.

Keep the factory air box. I don't fully understand exactly why, but large airbox volumes help mid range torque production. This was a big thing when the 600cc class was reaching for 90 factory hp, they had really soft mid range and huge air boxes even before the filter helped. For maximum top end individual filters can show a benefit due to increased flow, but it kills bottom and mid range. A K&N may help a tiny bit, but when using it for mileage you probably won't see much pressure drop across the stock filter anyway. Stock filter better anyway.

Keep up the good work! I'm rooting for you to see several 100+ tanks.
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