CBR650R MPG am I missing something?

silverlight7

2019
CB650R
Aug 11, 2021
Riding Since
2020
I think I figured out why I was getting low MPG. After my last post, I calculated the MPG manually, and I got a 42 MPG average, whereas the bike's computer thought I got 38. So the bike does estimate a bit low.

However, I just replaced my aftermarket exhaust with the stock exhaust yesterday, went for a ride, and I noticed that the instantaneous MPG calculation was much higher than before. On average, I was getting 10 MPG better than with the aftermarket exhaust: 50-55 MPG at 55 MPH, and 40 at 85 MPH. This seems much more consistent with the readings other people here have gotten.

I guess the lack of restrictions (i.e. catalytic converter) in the full exhaust caused the computer to richen the fuel mixture? The aftermarket exhaust (Black Widow) used the O2 sensor, so that's the only thing I can think of.

Gonna have to gut this stock exhaust though. I love the way it looks (Black Widow was ugly), but it doesn't sound nearly as good.
 

Ian Warren

2021
CBR650R ABS
Mar 12, 2022
United Kingdom
Riding Since
2019
One question comes to mind!
If you hit the stock exhaust will you just end up throwing off the engine, O2 / ECU set up again and screw the MPG all over again?

Don’t know that it will but perhaps some more research and look through the posts and ask some questions on the exhaust pinned post.
 

silverlight7

2019
CB650R
Aug 11, 2021
Riding Since
2020
Yes, that would probably happen, but I would replace the ECU with a Power Commander and get a custom tune. That should help keep the MPG. Even if a tune doesn't help the MPG, at least it would get me more power, which I would be willing to trade for some MPG.
 

Peteblue

2019
CBR650R
Jun 5, 2019
Not sure where the added MPG come from but here is an excellent article on the subject.
BTW ethanol has a higher octane rating than pure petrol so if anything your bike should run smoother with E10 and the ethical contains more energy in it not less.

Various tests and figures have purported to show various decreases in MPG using E10 vs E5 but it’s conclusion is it’s unlikely to make more than about 1 MPG difference on a modern bike with an O2 sensor.

My own experience (My son who I ride with often) has a Ducati V4S and a fat wallet) usually feeds our bikes the finest E5 super unleaded tank after tank, I haven’t seen any significant difference when I go back to being a cheap bastard and using E10.

Here is the article, worth a read.

I remember years ago when I was a teenager in the 70's, 3 of us had the same bike, Yamaha RD 200's. If we went on a decent run for the day, I always put less fuel in my tank than the others, and we were riding along together. I guess I'm just an economical rider.

As for my CBR, I was getting around 62 MPG, less with an enthusiastic right wrist with E10 fuel according to the display on the dashboard. I started to put E5 in, and my MPG went up to around 68 MPG. My local garage didn't have E5 fuel for a while so I had to put E10 in for a few weeks, and my MPG fell back to it's previous level.

A month or so ago, E5 fuel was available, so I started putting it in again. Initially, the MPG display on the dashboard didn't change, but over the time I have been using it, the reading has slowly changed and improved, and today, on a short 50 mile run, it showed over 70 MPG, finally settling down to 69 MPG by the time I got home.

I'm stating the figure shown on the dashboard, which I am presuming is correct, but it took a number of weeks and hundreds of miles before the stated MPG startted to improve.
 
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