[Turbo DV8]

I've had my new CBR250 out on two good rides now, and I've noticed a glitch in the fuel metering, but haven't noticed anyone else here having experienced it. When decelerating in any gear, as the tach drops through 3500-3400 RPM, there is a faint but noticeable hiccup in the fuel metering. It feels as if the RPM's want to pick up for a couple revolutions of the crank before continuing to slow down. Being faint and so brief, it's not going to cause control issues, and since 3500 RPM isn't a cruising range, it is only noticed upon decel. But it does it every single time, so I think it might be a EFI mapping issue. I am just curious if anybody else has noticed this nearly non-issue in their bike. How about a homework assignment, class? Everybody take a ride and see if you can recreate this upin decel at 3500 RPM! Hey, it's a good excuse to take a ride, right? In the name of science...

 

[stumps]

Yeah Turbo..mine's the same....that's the fuel injector coming back to life.

With the throttle position sensor in the closed state and engine speed > 3500 rpm or there abouts, the ECU shuts off the injector....get under that engine speed OR open the throttle off the closed position and it cuts back in.

 

[Turbo DV8]

Thanks for the reply. Although it's nice to know it's not just my bike, do you have any idea why the fuel injection should "turn off then "come back to life" right at that point?

 

[stumps]

Thanks for the reply. Although it's nice to know it's not just my bike, do you have any idea why the fuel injection should "turn off then "come back to life" right at that point?

It's typical for alot of efi systems. I have an old Merc V8 with ancient Bosch D-Jet efi that works similar...fuel off at 1800 rpm increasing and turns back on at about 1300 rpm decreasing....if the throttle is closed. I can hear and feel the sweet exhaust note change, just like the CBR, when it cuts back in.

I guess it seems about right for that little 250 to get the fuel back on well before the idle speed of ~ 1500 rpm.

 

[Turbo DV8]

Does anybody else feel/hear this hiccup on closed throttle decel at 3500 RPM? Also, especially when the bike is cold, I can also feel 3500 RPM as a dead spot when delicately accelerating in first gear through 3500 RPM. once I hit 3500 RPM, it falters, and I have to give it more gas to get engine speed to increase above 3500 RPM. If this is indeed all "normal," my question is why? Why should there be a jerk at 3500 RPM? Why is it necessary to cut the fuel off and back on over the span of several engine revolutions? And if it is not necessary, why does it do it? It is getting more annoying to me. Notice I didn't say it is getting worse, just more annoying, because none of my 28 year old CX650 Turbo's with ancient fuel injection exhibit this anomaly present on my brand new bike. A main reason I bought this bike was because it's fuel injection can better cope with our California crap gas, but now I have to coast down with a hiccup every time I decel. Unless there is some fantastic reason why fuel injection should hiccup, it is not acceptable on a new bike.

 

[Turbo DV8]

Went to the dealer, and their floor model does the same thing. Pretty annoying, considering it's a Honda.

 

[sendler]

Went to the dealer, and their floor model does the same thing. Pretty annoying, considering it's a Honda.

I ride around on and off the gas at 3000-3500 in sixth all the time and have never noticed it.

 

[Aufitt]

I dont think my bike has ever been below 6000 since its run in.

 

[Turbo DV8]

I rode in such a way yesterday which caused the anomaly to be even more apparent. I was in third gear coasting down an incline, using only the engine braking. The prolonged incline matched the third gear selection in such a way that the bike was coasting right around 3500 RPM. beginning just above 3500 RPM, when the bike gradually slowed just under 3500 RPM, I could feel the bike decelerate a little more, like someone had just let off the throttle, except the throttle was already all the way closed. Then it would right away almost imperceptibly pick up a little speed, get just past 3500 RPM, then decelerate again. Then when it dropped just below 3500 RPM again, it acted like someone let off the throttle further. I could also hear a change in the exhaust note when it acted like the fuel injection was shutting off further. Certainly nothing to make one lose control, but definitely a reminder that there are electrons controlling the fuel delivery.

 

[sendler]

That must be the speed that the decel fuel shut off comes on and off. A good programmer will use more hysteresis than that so the fuel shuts off on closed throttle decel until 3,000 rpm where it reengages to catch the approaching idle speed but won't reset to do another shut off cycle until the rpms go above 3,500 for example. So it doesn't just keep cutting on and off right at the same speed while you are coasting down a hill.

 

[stumps]

..A good programmer will use more hysteresis than that so the fuel shuts off on closed throttle decel until 3,000 rpm where it reengages to catch the approaching idle speed but won't reset to do another shut off cycle until the rpms go above 3,500 for example...

Agree Sendler. For a 2011 generation EFI, I reckon the cut in/out is a little bit harsh and should have at least some sort of deadband or other smarts to smooth things out....guess being a single slug mini thumper that's what we get. But who can really complain with the awesome fuel economy this baby returns......AuFitt's V8 gulping F1 revving version excepted.