why the crappy gas mileage?

I've heard that xj650s even when in great shape only get low 40's at best. Is there any specific reason for this? Any ways to increase it at all? 40 is better than cars get but not by all that much.

 

Sounds about right for the displacement, weight and technology. Shed a few pounds of steel and aluminum, improve the fuel metering system, punch the cylinders out a little and you should reach your goal. How's that?

 

On in my case - loose 20 pounds, tuck in on the tank and put a small windscreen on.

I get 34mpg +/- 4mpg.

Check the condition of the fuel fuel, carb, and exhaust system. Leaks and wear will degrade fuel milage - as will improperly tuned carbs.

 

im not for sure of my gas milage because i dont know how big the tank is i know that on my 82 maxim 750 i can go 100miles on a haf a tank according to the fule gauge mind you i guess ill have to figure it out next time i fuel up

 

How to check your fuel milage on any motorcycle:

Next time you stop for gas - make sure you fill it to the neck. Zero the odometer.

Everytime you stop for gas after that fill it to the neck - and write down the odometer. Zero the odometer. Divide the miles by the gallons and you've got your answer. The only way you can mess it up is by not zeroing the odometer or not filling the gas tank to the top. If you stop early and fill a half full tank it won't matter - you'll have gone half as far on half the volume of fuel.

Personally - I like keeping a fuel log - it gives me an idea what the bike is up to. Long term changes in fuel milage indicate changes in the engine.

Cheers,
woot.

 

New I got about 49 mpg on my Seca. But my Maxim after a carb cleaning and sync has only gotten 46mpg. This has settled down to about 42mpg. I guess I got good gas in Texas and since it was all highway miles with a good warm engine it was all in my favor. Combination city/hwy is about 39mpg.

 

Last month i was recieving 40 mpg now im down to about 37 36 range. My driving really hasnt changed so it must be something with the bike.

 

Don't forget that air temperature can affect our gas mileage since our bikes are carbureted...

 

I run my tank until I hit the reserve and get gas, fill her up.

I get about 100 miles and thats it.

Probably will be better after getting it tuned @ the shop.

 

I have a recorded 52MPG on my '82 650 Maxim - but that was when I first got it... Since then, I've only been getting from 35-45 MPG - depending on riding style & tuning... I can probably do to have some more accurate tuning - but I'm happy with what I have at the monent.

Rex S.

 

I have a 81 XJ 550 Max and I get between 45-60 mpg. I'm thinking of doing some gear changes to increase my MPG. (given the greed at work in the "powers that be" today)

Kelly

81 XJ 550 Maxim

 

what would be optimal gas mileage for a 82 750 seca? You guys that are reporting gas mileage in the 50 mpg are running smaller bikes. What are some steps that i can do to improve gas mileage.

 

Best I ever got on my Seca was 49. I would think that with 20= years of age 40 to 45 would be ideal.

 

On my '82 650 Seca, I seem to be floating right around the 43 mpg mark. I need to re-synch the carbs, but otherwise, it still beats the 18 that I get from my truck.

 

You are a riot Sno! I just trimmed off 15 pounds myself. Feels better too (hey, my old jeans fit again too).

 

I'm in the same boat SnoSheriff... I'm a fairly solid blue liner now, trimming 30 lbs off would be a good idea - and certainly make it easier for the bike to pull me around.

The next best thing to do is become more aerodynamic - I'm still working on shrinking my shoulders

 

hey guys ive got a 650 and i got 3.5l/100km on the weekend. i was amazed the bike was running a bit lean so thats why it was so low, all freeway pretty much sitting on 100.
the bike is in at my tuner getting jetted and synced atm. cant wait to get it back :lol:

 

When it was explained to me:

There are two factors that affect fuel mileage on a bike, those are
1. aerodynamics.
-despite what one might believe bikes are not very aerodynamic especially the maxim with no fairings, there are many paths for air to go through, therefore create lots of drag. There was a teardrop shaped 2 wheeled vehicle with a 300cc or so engine, built in europe that was getting close to 80-90 mpg on the highway sumply due to it's shape.
2.Engine.
Generally motorcycle engines with a displacement larger than 400cc are meant to be recreational vehicles ergo gas mileage is sacrificed for all out performance. The engine was built around performance. Not to mention the giant fuel line leak we call a carburator is not the most efficient mode of obtaining an ideal fuel air mixture.

Point being if we all had teardrop fairings and efi port injected engines there's no reason one couldnt see up to 100mpg from such a vehicle.

Very practical but where's the fun in that? I'll stick with my parachute bike.

 

I just did a run of about 550 miles. Averaged 40mpg US. I had to do some fancy converting. Liters per Km to miles per Imperial gallon then to US gallons. My butt is usually sore when it's time to fill up again! '81 550 Seca.

 

Another point to consider, would be proper tire size/inflation. I have an '82 750 SECA with stock size Metzler Lasertecs running 30# and 42# front rear inflation. I am getting over 150 miles to reserve. Once I get her tuned, I will do actual fuel mileage calculations. I believe I am over 50 mpg though.

Nachoman

 

Man, I sould bring my bike down to you have you tune it. Although the seca tank is over 4 gallons, isn't it about 4 gallons to reserve meaning you around 40mpg?


I run Bridgestone Spitfires with 34/36 psi front/rear and up it about 2 psi in the rear when carrying luggage. I get 40-42 mpg around town and 37-39 mpg on the hi-way. lol and about 27mpg when riding in the Rocky Mountains (yeah it doesn't like elevation).

What I don't get is the Honda CB750 gets in the 50's and aren't the XJ's Yamaha's answer to the CB? My brother has a CB750F Supersport and it would get mid 50's around town and low 50's on the hi-way. He just put a 900 engine in it and now it still gets better gas mileage then me, low 50's around town and high 40's on the hi-way

 

I was getting in the mid thirties. Got the carbs rebuilt. Now getting 50+.

 

I've checked with my doctor and she recommends I get my carbs jetted as opposed to losing 30 lbs for increased performance.

I guess 135lbs wouldn't be the optimum weight for a guy thats 6' 2"


I keep reading all these posts about pod airfilters and carb jets....makes me want to do it more and more. Maybe I'll be able to afford it before winter settles in.

 

My bike get between 43 & 49 miles per gallon depending how I run'er.
Once I got 52 mpg but I don't know if I figured it right because I can't do it again!!??
I was cooler weather then?!

 

On my first 81 Seca 750, I could get 45-50MPG depending on riding conditions. It wasn't in tip-top shape by any means, but it only had 18,000 miles on it.

Then I got an 82 Seca 750. It was in GREAT shape, was well cared for with only 9500 on the clock and I could only get around 40-42 MPG out of it!

Now I presently have another 81 Seca 750, in great shape and well cared for, with 11,000 miles on the clock and I can get 45-50MPG out of it!

Maybe the fuel economy is just better in the 81's for some reason? Were the carbs or the jetting changed on the 82's?


Chad

 

I get about 45 - 50 MPG on my 82 xj 550, all depending on how I drive. Just put a windshield on it, so will have to see it it improves mileage or makes it worse. Oh Its only got about 13000 miles on it, and I am running Michelin Macadam tires on it and using Mobil Super gas.

 

Last time I checked, I was getting low 40s. But the bike is in dire need of a valve adjust(shims on the way), and a carb sync. So after that, I'll have to recheck the fuel economy.

Of course, my 40 might be off, as I later had a speedometer failure(the 2 teeth on the gear were broken), so I might have been recording lower mileage than actual. And my bike only has 8000 miles on it too.

 

The reason the Honda might get more gas mileage is because we have shaft drive and I believe the Honda is chain driven. The power loss from driving the rear wheel at a 90 degree angle (hypoid), as opposed to direct drive (chain) is tremendous! I want to say around 10%. This would decrease our gas mileage accordingly because our wheel power/cc ratio would be down on the Honda.

 

Speedwagon, where did you get those shims?
How much did they cost?
I may need to be looking at those questions as my bike can use a valve adjustment too.
Mike

 

YICS was added maybe? Yamaha claimed a 10% improvement in mileage.

 

YICS was on all the 750 Secas, 81-83. But you did get me thinking... maybe the YICS passages were clogged up a bit on my 82??

 

YICS was on all the 750 Secas, 81-83. But you did get me thinking... maybe the YICS passages were clogged up a bit on my 82??

 

Keep in mind that the Maxim 650 was an 80's performance machine. See what kind of mileage an '83 Trans-Am with a 350 gets. Here is a list of some things kill the Maxim's MPG.

1) Shaft drive is less effiecient (But better in every other way)
2) No fairing causes poor wind resistance.
3) High performance 2-valve engine means big ineffecient vavles.
4) All riders of mid-80's rice-burners are really fat; causing increased wind resistance and rear tire wear. Also, nacho and twinky debri often gum up the carbs. Switching to a full-face helmet may alleviate this problem.
5) Valve lash is often neglected in older bikes, and can result in poor fuel economy.
6) Comfortable rear seat often results in the wife coming along for the ride (see reason #4)

 

I wonder what the math is on weight and horsepower, cuz I need to lose about 30 pounds before August 2nd if I even hope to do the trip I have planned out. 235 pounds down to 205 pounds ought to save me quite a bit of gas... and Cheeto money to.

The only problem is my trip is planned around brewery tours of Eastern Europe so my mileage will go down as the trip progresses.

 

Horsepower won't change as you shed pounds, but city economy will. Your bike's engine can really only generate a fixed amount of power given tuning and other things, but every time you accelerate, the bike needs to get your keester moving. Take this:

Force = Mass X Acceleration (Newton)
-Mass is you plus bike

Force X Distance = Work

So the more your weigh, the more you bike has to work given a consistant acceleration, the more gas the bike will use to get up to speed. Same goes with cars and junk in the real trunk.

Generally speaking, pods and exhaust will decrease milage. An engine is basically an air pump. The freer it can breathe, the more air it can move, the more fuel it needs to mix with that air; the more power it makes. But there are exceptions of course.

Hypoid bevel gears are generally about 97.5% efficient when not submerged in oil. Unfortunately ours are half submerged which reduces their efficiency do to oil churning (which is why the oil gets hot). Our bikes have two sets of bevel gears so assuming 96.5% efficiency, per set, we get 3.5% losses, squared which equals 87.75% . Chains are generally around 98%+ efficient IIRC which may help explain the economy differences between the XJ and the CB.

 

also for all you people who have with in the last year or two noticed a decline in the MPGs of your bike car truck ect must remember that the gas is different now with the ethanol in our gas. i only know this cause we have people bringing their bikes in left and right saying the carbs are screwy or their truck isn't getting the fuel economy it use to. the new gas is much less efficient no matter what the govt tells you i see it first hand. also it can eat away at fuel lines and add water to your tank which reduces fuel economy even more. ethanol will actually extract moisture from the air and deposit it into your fuel tank. many a time i have had to drain fuel tanks on equipment and vehicle's because of large amounts of water in the gas. also NEVER leave the new fuel in the bike for an extended period of time, like over the winter. old timers would tell you to top off your tank for winter storage DO NOT do that anymore cause you will clog and even get rust in your carbs from the water.

it was really nice of the govt to tell us that but then again it is the US govt they tell you only what you want to hear

 

Well said. All part of the plan my man, all part of the plan. Just when fuel prices are getting unbearable, the government steps in an worsens the problem through policy. Not only does the ethanol harm fuel, but it has made food pricier.

I bought a bike precisely for the reason of rising fuel prices. I can feel the pinch now, and it's nowhere near the $5+ a gallon the globalists are hoping for.

And if you think this is all by coincidence...I have a bridge to sell you...

Now, back on topic.

Duane

 

A lot of good info here.
I'm concerned with the milage that I'm getting, the manual says 47 mpg.
So for a 26 year old bike I figure 40 would be good.
It seems most 650 owners are realizing between 35 and 40 mpg.
I'll keep my fingures crossed.
Still got half a tank, by eyeball, and just reached 100 miles, looking good.

 

Yes, ethanol has about 70% of the energy per gallon of gas. So if you have a 10% ethanol blend, your new blend has 97% of the energy of straight gasoline. Also, reformulated gasoline has also been "cracked" into better burning short chain hydrocarbons which reduces the energy density. Gas of today isn't like the gas that was available when our bikes were new.

 

I'm getting 46 with my 81 XJ 550. Carbs are running a bit rich. Should look into that...then I'd probably be doing better...who knows, maybe not?!?!

 

Second tank full after carb cleaning, much better then the first.
I got 35 mpg.
Was hoping for something closer to 45, but it seems in line with what others are getting.

 

Wel, my 2005 honda ruckus gets about 75-80 mpg on city commuting - I may be kicking myself in the butt, as I just transfered insurance to the '83 maxim 400 today. Another fellow I know in town with the same bike gets around 50-55 mpg, but he figures he should be able to get 60 if he fine-tunes the bike...

On the other hand, now I can go over 50 km/h, and stay the speed limit going uphill!!

 

I have been getting around 35 mpg on my XJ 650. Yesterday I did some mixture tuning using plug chops. I know my #4 was running very lean and 3 was somewhat lean. I don't have it perfect yet but on a ride yesterday I did notice I was now running 200 to 300 RPM less at 55, 65 and 75 mph. I assume that I got more power via the tune so hopefully this translates to more mpg.

I ordered a colortune to do the mixture settings right.

I also put half a can of seafoam in. I ran a few gallons at the normal concentration last week. That should help clear out any build up.

 

Partially correct. Ethyl alcohol (ethanol) is hydrophillic like brake fluid and readily mixes with water from 1% to 99%, including atmospheric moisture. The ethanol used in our fuels (for the last 10 yrs in my home state of MN) is anhydrous (without water) so it mixes readily with gasoline. Unfortunately, if it sits for a LONG time in a non-sealed fuel system (old cars and trucks before emissions systems, all small engines, and many motorcycles) it can absorb enough water to come out of solution with the gasoline. It doesn't "deposit" the water into your gas tank and stays fixed with the ethanol. Ethanol is flamable down to about 70% (140 proof) but it will come out of solution and wreck havoc on the air/fuel mixture. If you ride frequently, you'll never have an issue with ethanol. My bike gets over 45 mpg easily with Milwaukee's reformulated and oxygenated gasoline.

Now, as soon as the democrats get their fingers out of the free market cookie jar we'll be back to normal gas and more oil wells. Just because the poor oil companies have land leases doesn't mean there is oil there to be extracted.