With the current riddiculous cost of fuel , the mpg of your bike must be a consideration. I recently sold my Honda 1000 VTR gas guzzler which would barely exceed 100 miles on a tankfull. My old 99 appears to be far more practical as it appears to be doing around 100 mpg !!. I would love to report that this is the result of a meticulous tuning session and blueprinting of the mechanicals , but no its mostly accidental and wear related. For some time I was obsessed with getting a slow and even tickover in order to improve the neutral selection, but I was plagued with sooty plugs and intermittent ignition I experimented with ancient non standard plugs, home made carb jets and valve settings. In the end some carefull clutch fettling did the job . I now have a nice slow regular tickover and the bike will happilly tick along at walking pace on no throttle in 2nd gear . It can start with one feeble kick , BUT, the mixture is weaker than it should be and there is an occasional hiccup just off pilot. No amount of fiddling with pilot or slide cutaway has the slightest effect on the hiccup which is likely to be wear on the chamber. In the meantime I am marvelling at the bikes ability to ignore petrol stations when my riding companions are filling up!. I looked up a road test of the 99 and they managed over 100mpg ,so it is possible ,350 miles on a tank.. Get tuning.
Economic Norton's. Dross Alert
Fuel price is crazy and not going to get better any time soon. All engineered to be this way and a political matter, so I'll leave the reason for it there...You know why.
I don't have a twin carb bike anymore. When I changed my 850 Mk 3 Commando over to a single Mk 1 Amal, MPG increased from 45 mpg to 68. No big reduction in performance either.
I must start riding my as new 1960 99, still only 450 miles on the clock, to see it can better my 57 Model 50 at 93 mpg that seems to be a constant figure.This even after increasing main jet up a size and moving the needle to richest setting. Should be perfect when I get to change the slide to No 3. Problem is that some of the new Amal Mk 1 main jets are not the same diameter. But at least 95% of weak running is gone. Not much pop bang now and no hole in the +30.
I'll be interested to know of tricks to increase MPG. Raising the gearing by one tooth on the gearbox is a favourite of mine, though one chat in NZ suggested it pus strain on the gearbox.
Not in the spirit of riding of course; riding style is a thing, such as not opening the throttle before the engine has picked up or racing to the junction and then jamming the brakes on.
Finally, as a matter of safety; if you see Chem trails in the clear sky and need to ride then please at least wear a visor. Take care.
I've always found...
... that MPG is more related to riding style than anything else. I've had similar figures (mid 50s) from a Commando 850, Triumph Tiger 955i and Guzzi V50 - the only ones I've bothered to check on. All cruised at 70-ish and acelerated briskly but not tyre-shredding. I also tend to use higher rather than lower gears, which suited all of those bikes.
My modern bike has a fuel…
My modern bike has a fuel computer and it's obvious that speed, acceleration and heavy backing are the main cause of high mpg.
But Iv had my Commando for 38 years, when I could first fill it up with 4* leaded for £1.50 and it would do 110 miles on a roadster tank....Now it cost £24 to fill it with Esso Supream and it will do 90 miles..
Make of that what you want, but it usually starts reliably and Iv had no damage/gum caused by ethonol.
It has also done plenty of miles on the cheapest supermarket shit petrol with no problems, as has my Model 19 rigid.
I once did an economy…
I once did an economy exercise with a twin carb 1725 cc Hillman Hunter, the journey was mostly by motorway and from memory mostly 50/60 mph . The car averaged 52mpg over 10 gallons . The carbs were Stromberg CV which ran pretty lean. As you say Peter ,its all down to the driver.
It's all about riding/driving style
I rarely use the brakes except when coming to a dead stop. I let the speed drop as I climb hills, let it increase downhill. I don't hang around particularly, just ride smoothly.
I haven't checked bike mpg for years but my B31 does 250 miles from tank full to tank empty.
My 99 always gave 75 mpg except when the needle jet became worn when the fuel consumption would increase telling me it was time for a new jet.
An interesting point is that I get 100 more miles to the car's tankful than my wife does.
For the 850's Norton cured a pickup from low revs with a snapped open throttle issue with the cutaway spray tube and the special needle in Concentric carbs. I helped someone fix the same issue on a pre 65 Trials Tiger Cub by using the same parts in a concentric carb. If you have a Concentric carb it may be worth trying it out. The explanation I have seen, which may be made up rubbish, was that the cutaway in the spray tube allows a small amount of fuel rich air on tickover that gets released on raising of the slide and gives a short duration of rich mixture that fills in the normal weakness. Anyway the Tiger Cub won a few trials after the mod with the much improved throttle response. I also run a B44 with an 850 carb with only a main jet change and that also has no issues at low revs followed by rapid opening of throttle.