Hi Daniel, Congratulations on your excellent fuel economy, very impressive. How fast is your CBF 125? Can it go 80 mph? Here in the USA a motorcycle must have at 15 bhp to be allowed on the freeways. Its too bad that Homda and the other major motorcycle manufacturers don't sell fuel-injected small displacement bikes like in Europe .
As far as better fuel economy , ride smooth, corner hard, avoid braking, coast when you can and use low RPMs to accelerate and cruise. You could change your chain drive sprockets to reduce RPMs if your bike has enough torque. Keep your tire pressures up. Consider more aerodymanic streamlining like I'm working on. Check out the Craig Vetter website and his work on the Freedom Machine.
All the best , L&S
Last tank, did 1081.1km with 15.70L of gas, it means 162mpg.
Some tips to improve my mileage?
I shut off engine at every "downhill", 40km/h at flat roads, climbs usually fix a certain speed, like 30, or 35km/h, @ 3300RPM, idling as most as i can..and so on
Do you have a modified tank on this bike? Factory data mentions a 10l tank (but even that could give you great range at 162mpg...)
Anyway, I don't think I can advise you wouldn't already know. Pulse&glide, maybe? I often do that, especially when not in top gear, but I don't know if it's of any use with such a small bike, in top gear. It's less useful even on our 250 than on the 650. At (low) highway speeds, at least. But you seem to move in a very different range. It may work, who knows.
I think works fine the more throttle & lowers RPM's, up hill
It makes sense, even though I've never seen any BSFC data about motorcycles - but gasoline engines are usually more efficient under load. Therefore I always try to keep rpms as low as possible and load the engine. In lower gears it means P&G for me. Especially downhills.
(Teresa's gearing is quite different, I can't shift into 5th under 70km/h and 4th under ~50. It's a lot of P&G for me in town. She's just too strong not to P&G.)
One little thing you should try: use like 80% throttle instead of WOT, under 100% load BSFC diagrams tend to show worse efficiency again.
BSFC is Brake Specific Fuel Consumption. It's a way to measure engine efficiency (fuel used per energy produced; how efficiently it turns fuel into energy; not the same as vehicle fuel economy but certainly an important part).
Generally, modern car engines make energy most efficiently (low BSFC) when almost fully loaded. Wider throttle and lower RPM reduce pumping and reciprocating loss. I don't know if it applies directly to carbureted motorcycle engines.
You can google for BSFC and read more about it or look at BSFC maps.
I don't know about the modern Honda singles, but the 1970's era single cylinder Hondas I've worked on (75cc, 100cc and 125cc) all had a sliding tube that served as the throttle valve in the carb. It was directly operated by the twist grip throttle. Connected to the sliding tube was a tapered metering rod that richened the mix as you moved closer to wide open throttle. The twin cylinder motorcycles that I've owned used a butterfly throttle valve and the metering rod that richened the mix was operated by a vacuum diaphragm- probably based on venturi vacuum (airflow).
My point is that if this bike has the metering rod directly controlled by the throttle position (twist grip throttle), upshfting early and using WOT/low rpm to climb hills may end up using more fuel because the engine is running really rich.
If this bike has a vacuum operated metering rod, then WOT at low rpm will likely be a good strategy.
If you look closely at the carb, you can tell the difference easily. If the throttle cable comes straight out of the top of the carb (opposite the float bowl), it is a tube type throttle valve with integrated metering rod.
I think the modern CBF is fuel injected, at least it surely is in Europe (Daniel wrote he lives in Portugal), just like their CBR125 which I had been eyeing with before buying Teresa.
That bike should be pretty similar to the CBF in terms of fuel efficiency. I almost regret that I didn't get one, but given that I rarely ride in town, I probably couldn't get the same average - by far. For lower speeds, and especially 1-up use on shorter distances I'd surely choose a small displacment bike like this.