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Being in neutral while going downhill doesn't save all that much gas. And it's not a small hill that will get you. If you live in hilly areas the heat continually will build in your brakes. I've done mountain rides before with scooter riders and have literally seen smoking brakes. It's because people want to ride aggressively and accelerate out of turns and then brake hard at the next switchback.
So even though you might not push your brakes to their limits others will and quite easily too these weren't people with a knee out dragging. They were just having fun in a group ride. And unless you can control when and where engine braking occurs as in a manual transmission a freewheel coasting feature is a bad idea.
Engine braking and coasting are two entirely different things. Going downhill without giving throttle is actually engine braking, it's not coasting and I can tell you it's saving your brakes from a lot of overheating. If you ride a manual transmission motorcycle and pull the clutch in, even on moderate hills you'll build up speed real fast. The engine being connected to the drive wheels regardless of whether you're giving it gas does a lot of engine braking. But since you're going downhill and not giving it gas you're not saving fuel by going down the hill faster. Engine braking doesn't use appreciably more gas than simply idling, and idling doesn't use "buttloads of gas". Engine braking simply prevents brake overheating and there's no fuel efficiency penalty for it when going downhill. The hyper-miling technique of coasting is shifting to neutral and shutting off the engine to go downhill. Purely dangerous and shifting to neutral isn't that much safer. On a CVT if you need to use the throttle the transmission spool up also will kick out your rear and cause you to possibly crash.
And comparing the KLR 650 engine to the NC700X isn't just a matter of gearing. The biggest efficiency gain Honda designed can't be replicated on the KLR, it's the long stroke engine design. There's also a lot of smaller things that add up like efficient valvetrain design, intake and exhaust routing for efficiency, reduced complexity pumping systems for coolant and oil. Everything together adds up to efficiency. It's not just gearing like people assume. Remember I had a GS500F and after gearing the heck out of it with a +3 front sprocket which you can't even buy anymore, the bike had positively gutless acceleration. Put it this way my Buddy 125 could beat it off the line. So unless you want to completely gut the useability of the KLR you don't want to gear it up to achieve your fuel efficiency gain. Also you'll be sacrificing the long term durability of the clutch on my GS500F I had to replace it after only 15,000 miles whereas I know normally on that bike people replace it at 30,000. And replacing that clutch, unless you do it yourself will completely negate all the gas savings from using the high gearing. Going from 15 tooth to 18 tooth was bad enough on a GS500F which actually had enough power, a 17% increase in gearing and I'm not even an aggressive rider. I could imagine what going up 32% on an engine that doesn't produce enough power to begin with. I had a Honda Rebel and that jump in gearing is pretty much like starting out in second gear which was positively gutless on that bike. I know that can't be good for your clutch.
I've bought and sold probably 7-8 different Chinese scooters and a couple Taiwanese ones, this on top of my normal motorcycle buying and selling routines. Out of all of them only one had an odometer accurate within 5% it was the digital odometer on a Honda Helix clone. Every generic Chinese scooter with an analog odometer was grossly inaccurate, and surprisingly my Buddy 125 was too. And I've verified this with more than just Google Earth. That was just my recommendation for people wanting to get the true mileage readings for their bikes. I've compared it to bikes I knew were accurate on routes I regularly traveled, and used several of my GPS's to confirm the distance travelled, this is on top of plotting my route on level ground using google earth. My real Honda's, Suzuki's, Kawasaki's I've owned, all of them were within 2% accurate.
And the difference between 70 and 80 mpg is actually a lot. If I told you one car got 35 mpg and another got 40, you'd no doubt pick the 40 mpg car. That kind of a jump in efficiency pretty much is the difference between a regular engine and a hybrid and people will pay more money above the gas savings once you factor in maintenance, battery replacement, and the hybrid premium, just to get an increase of that much percentage.
I do know one thing I could try gearing up my Sym Wolf but I'd be crippling it's performance in exchange for just a few more mpg's which I know will only top out around 15% more before you lose the advantage of gearing. In my experience constantly gearing up won't get you much more mpg's past a certain amount. It's likely you'd get the same mpgs at a 35 tooth rear sprocket as you would a 31 simply because when you go higher you eventually take the engine out of it's power band at top gear and lug it more which wastes more gas. And your acceleration suffers which means in order to accelerate you end up using more throttle which uses more gas. And the way carburetors are designed at higher throttle usages you use more gas. The needle tapers are designed that way to prevent overheating when operating at high throttle openings.
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