'88 CBR 250R M19 50+mpg

[marcexec]

Hi,

I am a German living in Ireland.
I have to commute to Dublin so I started motorcycling because of the obvious advantages. Most of my commute is motorway, thus I am aiming for 120 km/h if weather and traffic permit it. It is ~130kms long: from: Collaghknock Gardens to: 53.299679,-6.175354 - Google Maps

This is intended as my little progress thread.

I like the way you can compare mpg (bigger is better) but as you can see above I am used to other measurements.
Since I have not found a way to enter metric values to this site, I started tracking my progress on Details: Honda - CBR 250R MC19.

Today I reached over 50mpg, so I was tempted to improve this a little more.

Mostly I intend to do modifications on the bike, maybe my driving style, but not the (average) speed, a commute of roughly an hour is enough.

Today I fixed the fairings a little (she was dropped before I got her, and thus cheap) and closed the air inlets int the front (see if it holds long, seems there are parts missing). Also, I lubricated the chain a little.
Generally she is a workhorse, as I have other projects, she might not get the full attention. For example, I could fix, maybe even modify the fairings with fibreglass but cannot find the time, yet.

I have been checking this site from time to time and been reading a lot, especially the tips. I very much appreciate any input from you guys.

Thanks in advance!

[marcexec]

for you guys to see what I am talking about, I made pictures, just for you

[theycallmeebryan]

Wow, what a bike. I wish we had those over in the States. Inline 4 cylinder 250cc.... revving to 20,000rpms.... must be a blast to ride!

The first thing i could suggest is leaving for work a bit earlier and traveling slower on the highway. Traveling 75mph (120km/h) is hurting your mpg numbers quite significantly. Slowing it down to 60-65mph (100km/h) will probably net you another 5 or so mpg. If you can swing it, drive like i do and only travel 55mph (85-88km/h). 55mph seems to be the sweet spot for highway traveling.

Question: What is your RPM's vs Speed when cruising in 6th gear on the highway?

The next thing would be to gear the bike down by either added a tooth in the front sprocket or dropping 3-5 teeth in the rear sprocket, or do both. This will lower your rpms in all gears. I went from a 14/45 (3.21 final drive) to a 15/39 (2.60 final drive) on my Ninja 250, and it helped my economy quite a bit. Remember though, by lowering the gearing you are effectively decreasing your acceleration. Since you are posting on a fuel economy website, im sure you are willing to sacrifice a little acceleration for fuel economy .

Finally, practice driving without brakes and engine off coasting. Pay attention to the traffic ahead of you and adjust your speed accordingly so that you do not have to use your brakes. When coming to stop signs or when you have to slow down significantly, pull the clutch in and hit the kill switch.

Most importantly.... drive safe and have fun!

[marcexec]

Thanks,

120km/h translates roughly to 11krpm, and yes, I am totally willing to sacrifice a little acceleration.
For the sprocket change, I was thinking in the lines that the 5th becomes as the 6th is now (end-ratio wise). Does that make sense?

I am also considering a bigger windscreen as I cannot hide at all behind that cut-off thing and I am 193cm (~6'4") tall.

[beatr911]

Your re-gearing target seems appropriate for a first try. Since us Yanks don't have that cool bike someone over there might be able to advise you on how high you can gear it. The peaky engine might not produce much power at 8,500-9,000 rpm. That, or you can be the pioneer. Use a Scottoiler or similar automatic chain oiler to reduce friction and keep your chain wear down.

A bigger windshield may help but go no higher than your shoulders, also keep the steep slope for clean non-tubulent smooth air flow. Also any baggage you might have should be out of the air flow. Put it on the tank, on the seat behind you or on your back.

Easy gains are also had if your carburetor jetting is not optimized. Some manufacturers jet some models quite rich, in these cases it's a win/win - more power and decreased fuel use.

Lastly please report back your results! We're all curious what changes positively affect your fuel use.

[marcexec]

Originally Posted by beatr911

Your re-gearing target seems appropriate for a first try. Since us Yanks don't have that cool bike someone over there might be able to advise you on how high you can gear it. The peaky engine might not produce much power at 8,500-9,000 rpm. That, or you can be the pioneer. Use a Scottoiler or similar automatic chain oiler to reduce friction and keep your chain wear down.

A bigger windshield may help but go no higher than your shoulders, also keep the steep slope for clean non-tubulent smooth air flow. Also any baggage you might have should be out of the air flow. Put it on the tank, on the seat behind you or on your back.

Easy gains are also had if your carburetor jetting is not optimized. Some manufacturers jet some models quite rich, in these cases it's a win/win - more power and decreased fuel use.

Lastly please report back your results! We're all curious what changes positively affect your fuel use.

Regarding the oiler, I am already considering this little gadget: About Tutoro

I was considering a windshield I am just able to hide behind if I'm neatly fully tucked. anybody has suggestions where to get one? Are there generic ones around or from a different model that might fit?

I had the carbs redone by a bike shop.

for my progress, check Details: Honda - CBR 250R MC19

I will update it every evening or the next morning, since I currently fill her every time I come back from work.

[beatr911]

The Tutoro sounds like a good unit. Years ago, I imported and used one of the first Scottoilers in the US and was quite impressed with it's ease of use, being vacuum actuated. The reservoir was good for 2 or 3 tanks of fuel and was probably 25 ml or so. I used a quality non o-ring (low friction) racing chain that was actually cheaper than a cheap o-ring chain. With the oiler properly set up, chain wear measured by strech rate was quite literally 1/4 the rate of the previous o-ring chain. This was using cheap 10w40 motor oil. Money in the bank if you plan to keep your ride for a number of miles.

When your carbs were redone, ensure they used an exhaust gas analyzer and a dyno to jet it properly. Installing a pre-made jet kit is usually intended to correct for aftermarket exhaust, intake, etc and does not accurately tune the fixed orifices for maximum fuel economy. It may run stronger but that is due to making some circuits overly richer than needed for maximum economy. Carbies are actually pretty complicated in thier operation and it takes a good specialist to really get them right, all others get them "good enough" and it's very easy to err on making them too rich, wasting fuel.

[marcexec]

got 51 mpg again: some EOC, fairings fastened, strong headwinds on the way home

From now on will switch to 1 1/2 day tank cycles, I found a cheap station at the motorway, for gas at least (I am used to compare diesel prices because of the cage, which is even older than the bike)

[marcexec]

Regarding my attempt to fill her only every 1 1/2 days - that failed, sort of.

I was trying to reach the station directly at the motorway but I had to switch to reserve after 210km on the tank. I filled her with 10.35l, that's all I can get int her. The tank is supposed to hold 13 Litres + 2 Litre Reservoir.

Even worse, since coming near the "end" of the tank, probably some old gunk got loose and now she's running rough at certain rpms...

Summary:

Never change a running system!

[beatr911]

I'm guessing it is water in the bottom of the tank now in your carbs. Try sucking some of the water, and gunk, out of the very bottom of the tank with a long clear hose. Also add a little fuel dryer (we have this stuff called HEET) to suspend the water until it gets used in the engine.

Also it is not a bad idea to intentionally use the reserve area of the tank. This helps cycle through any heavier, water laden gas that may be sitting in the bottom. Also it keeps the reserve circuit in the petcock clear in case you really need to use it some day.

Gasoline can absorb alot of water but too much settles out and obviously can cause problems. If your bike runs okay enough, just run another tank or two or three and the water in the carbs may clear out as the fresh gas that is cycled through absorbs the water in the bottom of the float bowls.