300 miles on a single tank CBR300R
 

I have done some testing with my CBR300R for better fuel economy.
It turns out that the bike is best tuned stock, and changing the gearing from 14t front sprocket, 36t rear, to a 15t front, 34t rear.
Note, not all 34t sprockets fit the rear. The chain can cut over the sprocket bolt at 34t.

The CBR300R has quite a restrictive exhaust system.
Equipping it with a freeflow exhaust, does open up the engine to rev freely from 1500RPM onwards, as opposed to 4000RPM with the restrictive stock exhaust.

But aside from that, without fuel controller, there is no easy way to increase fuel supply to the bike, as the bike starts running very lean, and loss of power is noted.

So the best fuel ratios are gotten with the stock exhaust.
The gearing did help me get just over 310 miles on a tank (3.5Gal) of fuel; or get a MPG of 87MPG on the bike.
Mostly keeping it pinned at 40-50MPH.

While the CBR definitely did not beat any MPG records, to do just over 300 miles on $8 on gas is astounding!



The open exhaust system does give an increase in fuel mileage above 7.5k RPM; and the bike revs more easily to 9.5k RPM.
I think the open exhaust helped raising the HP curve from ~27.1HP at 8.5k RPM to about 28.5HP at 9k RPM, at the cost of mid rpm acceleration or torque.
I would just keep it all stock.

Nice work

That is really impressive. I don't know the details of your bike, but mine only gets about ~150 per tank, or atleast that is when I fill up. I usually put ~4 gal in it. Terrible mileage really.:o

300 miles on a sport bike? Dayuum dude. Try hypermiling an ST1300 and see how far you can stretch that 7.7 gallon tank. :thumbup:

A note on your lean issue with the exhaust: I remember reading about exhaust mods on the CBR 250R and how the ECU would not compensate for the new exhaust, even after months of riding. You could reset the ECU (don't remember how) so it would properly learn the new exhaust so power gains, and proper fuel ratios could be realized.

The only thing I could do, was modify the cylinder temp sensor, making the bike run a bit hotter, by installing a resistor in series with it.
it would run a bit hotter, and give a small low rpm boost in power.

Then also the O2 sensor, it would help offset the mid range lean burn, but also run high rpm a bit too rich.

Stock isn't too bad. The stock exhaust gives backpressure, causing the bike to have more mid-range torque.
The CBR300R did well on roads below 80MPH; so if you won't try to surpass 90, there's no reason to swap the exhaust.

I didn't know why but the idea is very persistent

Changing the exhaust changes nothing in the carburetor
If you are getting into a higher RPM range and flow is more than
The carb can handle. Because of more fuel loss at overlap or whatever
Then you need a bigger, or more than one carb.
If you enriched the fuel to be correct at the excess RPM
It will be wrong for when you get back to normal
One of the nice things about carbs it's an easy swop

Yamaha Warrior 350 Performance Carburetor 1987,1993-2004 | eBay
Oh yeah I forgot to add congratulations you on a awesome tank

The CBR300R has a fuel injection system
Most modern bikes no longer support the much more easy to work on carburetor systems.

On my Kawasaki ninja 250 I wasnt going to fork out $4-500 for a exhaust system, so I took the exhaust off and drilled about 30 or more 3/8 holes in the header, then paid about $50 for exhaust silencer packing and exhaust wrap to silence it a bit!! Now it sounds like a mild Harley!! ���� and I also put pod filters on, and am now getting an average 75.5mpg. And after the last tank I installed a 16t front sprocket with the stock 45t rear.