Average MPG for 71 CB500/4 K? How to optimize?

[Catbird]

Well, not always "better" so much as just "wrong". In a newer car, a newer exhaust without proper ECU tuning means that the reduced backpressure tricks the engine into thinking it's running rich (rich burn means lower temperatures, means lower pressures, means less backpressure at the sensor), which will cause the car to lean itself out. Yes, this means slightly better mileage at the cost of burning out your piston rings and valves.

On the other hand, our bikes don't have computers.

The more you can do to reduce the amount of throttle you have to give the bike, the better.
Increasing your gearing will really help your mileage on the highway, BUT the fact that you have to beat on it more at lower speeds *may* actually make your mileage worse around town.
Capitalizing on the scavenging effect, that is, using a long, straight, clean and continuous exhaust pipe that isn't too large for your exhaust pulses, may cut-off your horsepower a tiny bit at the top, but the gains in torque will make it so that you don't have to work as hard to accelerate at low speeds.
You've got a 4-stroke, so expansion chamber tuning is really far beyond the point of diminishing returns for you.

IMO, the best you can do is use good motor oil, keep your chain lubed, keep good tires on 'er, go light on the throttle and tuck anywhere you possibly can. I got my DT up from 42 to 52MPG by doing this, and then again up to 56 by adjusting my jetting.

 

[SONICJK]

Well, not always "better" so much as just "wrong". In a newer car, a newer exhaust without proper ECU tuning means that the reduced backpressure tricks the engine into thinking it's running rich (rich burn means lower temperatures, means lower pressures, means less backpressure at the sensor), which will cause the car to lean itself out. Yes, this means slightly better mileage at the cost of burning out your piston rings and valves.

On the other hand, our bikes don't have computers.

The more you can do to reduce the amount of throttle you have to give the bike, the better.
Increasing your gearing will really help your mileage on the highway, BUT the fact that you have to beat on it more at lower speeds *may* actually make your mileage worse around town.
Capitalizing on the scavenging effect, that is, using a long, straight, clean and continuous exhaust pipe that isn't too large for your exhaust pulses, may cut-off your horsepower a tiny bit at the top, but the gains in torque will make it so that you don't have to work as hard to accelerate at low speeds.
You've got a 4-stroke, so expansion chamber tuning is really far beyond the point of diminishing returns for you.

IMO, the best you can do is use good motor oil, keep your chain lubed, keep good tires on 'er, go light on the throttle and tuck anywhere you possibly can. I got my DT up from 42 to 52MPG by doing this, and then again up to 56 by adjusting my jetting.

I wasn't talking about new cars, as computers make things much more complicated. Although since you brought it up
If you do tune the ECU you still get improvements in gas mileage without running lean, i have tuned many cars with CAI's and exhaust and every time it yields an increase. Shit my diesel went from 14 mpg to 24 with cai, exhaust and a tuner (i know i know diesels different, just wanted to post that because I'm quite happy with it haha)
I stand by my posts 8)

OP, the point of all this is is "less throttle=less fuel consumption" so anything you can do to decrease the amount you have to hold the throttle open at speed is going to aid in gas mileage.

 

[Catbird]

Agreed 100%.
Hope our goofy little not-quite-argumentative scholarly discussion has helped.

And more importantly, hope to see you enjoying your baby a whole lot before the end of the summer!

 

[Sonreir]

I'm getting in on this topic a little late, but aside from changing your riding habits, here are some technical solutions:

* If you spend time on the highway, change gearing to lower the revs (this may increase fuel consumption if you do a lot of stop-and-go riding, though)
* Increase compression of the engine
* Switch to a fuel efficient cam (might have to have one custom made, doubtful there's an aftermarket option for fuel economy)