fuel economey

Dennis C · Dec 24, 2014

I finished? my restoration a few months ago and now have 1000 miles on the restoration.

I took a ride yesterday 80 miles, average about 70mph. mostly highway/freeway riding tack between 4000 and 4500

The bike rides great, good idle good start and smooth throttle response. Passing up to 90 and still pulling strong.(took it to 100 the other day and it was still pulling.

The problem is it took 2.4 gallons to do the 80 miles. and that was when I had to go to the reserve.

Seems like pretty high fuel consumption

What are others getting for mileage.

It is a 1971 750 commando bored 020 over. complete top end rebuild

Dennis

Nater_Potater · Dec 24, 2014

11K miles on the engine, 22 tooth c'shaft sprocket, single 34mm Mikuni, and we're getting a very consistent 56-58 mpg US in mixed driving. With the Interstate tank, my butt gives out long before the need to stop for petrol.

More details on yours as to jetting (needle position and slide cutaway), final gearing, ignition advance, and the like, would help to better understand your plight.

Nathan

concours · Dec 24, 2014

You were caning it. Disregard that tanks mileage. Do a multiple tank average, report back. The reports of 50+ mpg are done at a pace never using the power/speed potential of the bike.

Dennis C · Dec 24, 2014

21 tooth sprocket twin 930 amals, 220 main jet, slides and needle are stock. I had the carb professionally cleaned and rebuilt, original slides. power arc ignition from old britts set per their specs

I have not done a proper plug chop, but when I checked the plugs they are a light tan at the end of a ride.

Dennis

Hobot · Dec 24, 2014

if not needing tickle or choke for one kick 1st starts then its too rich a tune. Almost all Cdo mostly still factory should get low to mid 50's mpg on sane use like freeways 80's mph all day long. A hot rod severely hot rodded can drop to low 30's mpg and geared up with lean tune or CV carbs claim 70's mpg. Plug chopping is always appropriate. Check float level by how many pilot screw turns out. More than 1.5 implies hi float for extra fuel flow, less than 1.5 implies low fuel level flow. Spark time too retarded makes engine work against more press but tend to show up as over heating. Big ole full dresser HD's tell me they get mid 50's mpg doing 60-70's for prospective with our kissing cousins.

kerinorton · Dec 26, 2014

Years ago I rode my 71 750 from Wellington to Auckland and average 70 mpg. I was lighter then though, and hardly went over 70 mph. Driven quietly, I got 63 mpg in my 74 850, while during the same trip, a Combat owner got only 40 mpg.
My 750 today has only cone 13,000 original miles whereas the 850 has done a hell of a lot but has had a fair amount of time spent on getting the carburation right.
I GUESS THE FASTER YOU GO, THE MORE FUEL WILL BE USED.

DERECK

texasSlick · Dec 26, 2014

concours said:
You were caning it. Disregard that tanks mileage. Do a multiple tank average, report back. The reports of 50+ mpg are done at a pace never using the power/speed potential of the bike.

I have to agree....my Atlas can get at best 55 mpg, and only if I cruise the interstate, keep the speed under 55 and the throttle tweaked. On a transcontinental trip in my youth, I averaged in the low 40's mpg at a cruise speed of 70, high 40's at a cruise speed of 60, and probably could have hit the low to mid 50's if I choose to cruise at 55. At the end of a 12 hour riding day, I found I could make the same distance down the road at 60 as at 70, due to fewer fuel stops.

A fairing would be expected to raise all the numbers. I would be surprised if someone could get an honest 60+ mpg at 70 mph without one. If I stand to be surprised, my Atlas is more of a fluke than I know it to be.

My general riding average is 45 mpg....that is, riding without regard to economizing, but not being stupid either.

Slick

Hobot · Dec 27, 2014

If not getting 50's mpg on 60-70mph cruise then its not normal in normal range either to some extra low gearing, only climbing mt in head winds or rather rich. Wes's '71 thickly coated HiRyder tank doesn't hold even 2 gallons anymore so we are very mileage/station distance oriented so rather familar with expected milesages in Mt twisties to Texas plains and hot doggie even beyond my comfort zone on un-tamed Cdo. On the otneher hand if unconcerned with economy vs thrills just how low a mileage has anyone d/t accelerating all the time for lots of wind resistance? Anyone know what Norton racers mpg range is?

gjr · Dec 27, 2014

If the plugs look good I'd say it is set up about right.

Power required goes up with the square of the speed. In rough numbers it takes a third more power to 70 vs 60 mph. 80 takes 1.75 times as much and 90 takes 2.25 times the power to go 60. Obviously this assumes that neither you nor the motorcycle change shape. Power = Fuel.

In normal touring (staying off the interstates mostly) I get about 50 +/- mpg.

Just for fun, some time when you are out on the highway set a constant throttle while in your normal riding position. See what your indicated speed is. Then put your chin on the tank and see what happens. Calculate the difference in fuel/power consumption.

Greg

gripper · Dec 27, 2014

Kerinorton, I guess you are using imperial gallons not US gallons

Dennis C · Dec 27, 2014

Is a plug test after a ride of any value? From what I have read they are only used at full throttle . I have looked at mine after a couple of rides after parking in the garage, Last mile at 25 30 mph and Idling down the drive into the garage. If that is any value as an indicator I can take a photo.

The tail pipes are black and sooty inside at the ends

Not yet so much concerned about full throttle as the mid range. and economy.

It seems to have good throttle response, it idles well, though at higher rpm after a ride. after warm up it has what I think is quick response both at the stop sign and through the gears. You know the vroom vroooom thing.

It does need to be tickled to start.

Dennis

comnoz · Dec 27, 2014

Dennis C said:
Is a plug test after a ride of any value? From what I have read they are only used at full throttle . I have looked at mine after a couple of rides after parking in the garage, Last mile at 25 30 mph and Idling down the drive into the garage. If that is any value as an indicator I can take a photo.

The tail pipes are black and sooty inside at the ends

Not yet so much concerned about full throttle as the mid range. and economy.

It seems to have good throttle response, it idles well, though at higher rpm after a ride. after warm up it has what I think is quick response both at the stop sign and through the gears. You know the vroom vroooom thing.

It does need to be tickled to start.

Dennis

With no lead in the fuel the insulator color is going to be meaningless. It should be completely white if you have good combustion. Any color other than white is going to be soot from incomplete combustion or burnt fuel/oil additives. Some discoloration would be normal with more mileage.

There is still value in looking for the temperature line on the side electrode or rounding of the edges of a non- platinum plugs center electrode. Jim

Dennis C · Dec 27, 2014

I'll take a photo, but as mine are tan can I take it that I am running rich in the low to mid range?

Dennis

comnoz · Dec 27, 2014

Dennis C said:
I'll take a photo, but as mine are tan can I take it that I am running rich in the low to mid range?

Dennis

I would not take that alone as a sign of richness. It would be a sign of poor combustion for some reason. Jim

gjr · Dec 27, 2014

Dennis C said:
I'll take a photo, but as mine are tan can I take it that I am running rich in the low to mid range?

My plugs run about half tan, about half grayish white by the time I get home. Stark raving white insulators scare me. If you get the top end right and the bike starts well, picks up cleanly and runs out smoothly, your carbs have got to be pretty close.

Take the bike out and run it at a steady 65 or so and see what you get for mileage.

Greg

kerinorton · Dec 27, 2014

gripper said:
Kerinorton, I guess you are using imperial gallons not US gallons

Is there anything else???

Dereck

kerinorton · Dec 27, 2014

Dennis C said:
Is a plug test after a ride of any value? From what I have read they are only used at full throttle . I have looked at mine after a couple of rides after parking in the garage, Last mile at 25 30 mph and Idling down the drive into the garage. If that is any value as an indicator I can take a photo.

The tail pipes are black and sooty inside at the ends

That's an indication you are using unleaded fuel.

Dereck

Nater_Potater · Dec 27, 2014

Also, make sure the AAU is working correctly, and that the full advance is where it should be.

Nathan

Dennis C · Dec 28, 2014

Here are photos after the subject ride,, the bike has been siting since then and I just pulled the plugs.

I may be just chasing fairies, I guess the next will be to test at a steady speed , do you realize how hard it is to not get on it? restraint on the Norton is not a natural thing, I mean if I did not check the mileage I would be a very happy rider.

Dennis

Hobot · Dec 28, 2014

Dennis. what turns out are your pilot screws set?

fuel economey

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