Fuel Mileage

Skip · Posted: August 8, 2009, 6:15 pm Post subject: Fuel Mileage

Hey Guys and Gals,just want to get some input.
Was out for a 150 mile ride on a beautiful day here in Nova Scotia.
26 bikes,all shapes and sizes,mine being the oldest
y first major ride on a new top end rebuild.Broke in with 500 miles
Figured out my fuel economy at 70.3 MPG. Seems to good to be true
150 miles,windy roads at 40 to 55 MPH.
Let me know, is this the norm for MPG?

xsleo · Posted: August 8, 2009, 6:59 pm Post subject: Re: Fuel Mileage

Sounds close, as long as your not running to lean it should be ok.

Joseph · Full Member Joined: May 22, 2007 Posts: 767 Location: NY

40-55mph do you have stock gearing? I am getting 43m pg all around town and parkway driving up to 70 mph usually about 60 on pkwy and whatever around town. I have 17 front and 30t rear. I am running a bit rich I think though. I was going to post a similar ? so I'll do it here.

y plugs look like the bike is running lean if anything, I am sure at cruise it is running rich because I think I should be getting a bit better mileage and I get no popping what soever on decel and I get a basey tone on excel, I have stock 34 w adjustable needle. And one size up on mains and piolet jets. I forget what notch the needle is at. I am thinking I have the needle to high so the pilot circuit is lean and everything else is rich, does that make sense.

Skip · Posted: August 8, 2009, 8:01 pm Post subject: Re: Fuel Mileage

No xsleo I don't think shes too lean,pilots set at 2 1/4 turns as per clymer manual,and my plugs show a little more dry carbon than they should so I believe they are rich enough. I have no idea whats in it for jetting or needle settings.I have owned this bike for 7 years and have never been right into the carbs.They have always worked so well I don't want to mess with a good thing.
Joseph, I am running 17 front and 34 rear on the sprockets which I believe is the stock set up for my 78. I am not able to give advice on the settings for your 34's. I'll leave that to XSjohn and the other pros on here.
I always say I rather give no information than give wrong information!

xsjohn · Posted: August 8, 2009, 8:28 pm Post subject: Re: Fuel Mileage

Starting in 80 they leaned them out.......good carbs just way too lean.......in order to say that your carbs are just right or to lean or rich you need to take cylinder temperature readings...and do check both sides.......the right will run 15-25 degrees hotter....any reading above 250 to me is not good.......and measured after say 15 or 20 miles at highway speeds........in tee shirt weather.......

In more temperate areas the mixtures can be a bit leaner but when ambient temperatures climb much over 75 degrees the engine can't dissipate heat as fast as it is generated.........fuel is the only coolant at that point.........the catch 22 always being cylinder and ring wash if overdone........which I see a lot of on this site with overly rich mixes..........

And a correctly set carb will run leaner in the winter and richer in the summer because of the air density differences......

And I wouldn't run mine with white porcelain even for a short distance........

50 mpg being a bit rich and 60 mpg being lean........53 -55 seems decent but then again gearing and rider weight play on mileage....white porcelain to me is not good...............

And lean mixtures won't necessarily give you better mileage..........because it takes more throttle and giving less power....and producing more cylinder heat..............and hot cylinders are not as efficient..........catch 22.............

xsjohn

Retiredgentleman · Posted: August 8, 2009, 9:42 pm Post subject: Re: Fuel Mileage

Skip;
Congrats on doing your top-end rebuild, and getting your bike back on the road.

Wow, 70.3 MPG. Since you live in Canada, I have to ask is that calculated with the american gallon or imperial gallon. It does seem to be amazingly stingy on fuel. If that was calculated on the imperial gallon, then that would be 58.5 american MPGs, which would seem to be more correct.

On a 344 km trip I was averaging 54.6 MPG (american gallons), but it was in the mountains. 17/33 gearing.

Actually stock gearing in Canada was 17/36.

pamcopete · Posted: August 9, 2009, 7:12 am Post subject: Re: Fuel Mileage

RG,

I was getting 57 MPG with the stock coil, Autolite #83 plugs and PAMCO on my '81/H. That went to 60 MPG when I installed Mikes 17-6822 coil, which has a longer spark duration. I just recently installed the Iridium spark plugs from Mikes and gained another 3 MPG to 63 MPG. The air filters are paper element replacements derived from Briggs and Stratton air filters.

1. The exhaust is EMGO 27" reverse cone mufflers.
2. Main jets are 135's.
3. All test runs were 60 miles round trip on highways with some stop lights.
4. Average speed of 55 MPH.
5. Tank refilled at the same pump.
6. Temperatures in the high 80's to mid 90's.
7. 17/33 sprockets with 16" rear tire.
8. Avg. 3808 RPM.
9. 93 Octane gas

Retiredgentleman · Posted: August 9, 2009, 11:20 am Post subject: Re: Fuel Mileage

Interesting fuel consumption numbers, Pete. That's a real eye opener when just the spark plugs can gain 3 mpg.

Since I have only measured my fuel useage when runing in the mountains, I will have to do a fuel test run on flat roads.

pamcopete · Posted: August 9, 2009, 12:33 pm Post subject: Re: Fuel Mileage

RG,

Well, I was also sceptical that just a change to a different plug could make that much difference (5%), but I did the run honestly and returned to the gas pump as soon as I got back. I also maintained a steady 55 MPH, but that was on all runs. Of course, just installing new plugs will probably give you a 1% improvement regardless of the type.

xsjohn · Posted: August 9, 2009, 1:59 pm Post subject: Re: Fuel Mileage

A fuel mileage test should include cylinder temperatures……at a steady 55 mine will easily get 58 mpg or so and the "cylinder" temps will be the same on both sides running at 235 degrees at 85-90 degrees ambient…which is down 30 degrees from stock temps.....and dark grey plugs......

BS34's

Custom 47 pilot jets
Custom R/L needles staged properly
Custom 134 Main Jets...

xsjohn

xs1961 · Posted: August 9, 2009, 3:47 pm Post subject: Re: Fuel Mileage

I got 38mpg today with 34mm VM's..warm & windy weather .. Shocked

xsleo · Posted: August 9, 2009, 4:49 pm Post subject: Re: Fuel Mileage

I get about 54 mpg at a steady cruise speed of 65 mph. If I cruise at a steady 55 the mpg's go up to around 60+. The book claims 70 to 87 mpg at a steady 37 mph, depending on model.

Skip · Posted: August 9, 2009, 6:21 pm Post subject: Re: Fuel Mileage

Hey RG You hit it right on the head!
I was thinking like a Canadian and not thinking that most folks would be talking in the larger US Gallon.
58.45 MPG. Sorry for the confusion and hope nobody thinks I was full of "you know what!"

Retiredgentleman · Posted: August 9, 2009, 11:53 pm Post subject: Re: Fuel Mileage

Skip, 58.45 MPG is excellent for these bikes. I'd say your engine and carbs are running pretty nice.

I remember back in earlier days I used to think in terms of Miles per imperial gallon; then the metric system came to Canada which completely screwed my mind. Now its just plain easier to talk about fuel consumption in those american MPG.

Ummmmmm .......... maybe we can get the americans to convert over to the metric system Rolling Eyes

Skip · Posted: August 10, 2009, 2:42 am Post subject: Re: Fuel Mileage

RG when the metric system came out in 76 I was in grade 6 and we were taught both through school.But I always found it easier using the standard measurements.Even to this day I talk MPG,LB etc. I spend alot of wasted energy changing all my figures over!(Math was my worst subject so that doesen't help either!)
As far as the bike goes she is working awesome!
I must say the thought of 70 MPG was "out there" and I was afraid to park the bike too close to the tool box!
58.45 MPG,now I won't be afraid to put a wrench on it now and then!
RG once again your wisdom and clear thinking solves another mystery!!

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