Topic: What's the realistic MPG for CB550?

[Kframe]

I've got a CB550 (1974) that I've been rehab'ing.  Just got it running on all 4 and managed to run a tank of gas through it this weekend.
Hit reserve on the way home so stopped for gas.  It took 3.67 gallons to fill to the same visual spot I was at last fill, and the trip gauge was at 122. 
That's 33 MPG. 

I didn't do a real plug chop, but when I got home I pulled the plugs and #1 had a smudge of black soot on the electrode and around the metal ring, but insulator white.  #2-4 all had very little residue, barely made a mark on my finger, insulators white. 
I don't really get much on my fingers if I wipe the inside of the tips on the Emgo's. 
So, I'm guessing I'm a bit lean, except on #1. 

Now, I was riding spiritedly this tank, whipping it up to 8000 before shifting, went 90+ several times, and probably averaged 70mph the whole tank at ~5000 rpms. 
I thought the 550 was supposed to get about 50mpg.  I know riding hard will decrease the figure, but by 17mpg?

 
-K

[MCRider]

I've got a CB550 (1974) that I've been rehab'ing.  Just got it running on all 4 and managed to run a tank of gas through it this weekend.
Hit reserve on the way home so stopped for gas.  It took 3.67 gallons to fill to the same visual spot I was at last fill, and the trip gauge was at 122.  
That's 33 MPG.  

I didn't do a real plug chop, but when I got home I pulled the plugs and #1 had a smudge of black soot on the electrode and around the metal ring, but insulator white.  #2-4 all had very little residue, barely made a mark on my finger, insulators white.  
I don't really get much on my fingers if I wipe the inside of the tips on the Emgo's.  
So, I'm guessing I'm a bit lean, except on #1.  

Now, I was riding spiritedly this tank, whipping it up to 8000 before shifting, went 90+ several times, and probably averaged 70mph the whole tank at ~5000 rpms.  
I thought the 550 was supposed to get about 50mpg.  I know riding hard will decrease the figure, but by 17mpg?

 
-K

I'm not a 500/550 guy, but I should think you would get a solid 40-45 anyway regardless of how you were riding etc.  I've read from other 500/550 owners that the mileage was sub-40 which seems low. My 650 Hawk gets 55-60.

So I wonder, how about wheel bearings, chain conditrion, tire pressure, etc. Somethings dragging you guys down.

[the technological J]

thats about what i always got....... there is a thread about drilling the emulsifiers out  and getting better gas milage but i cant find it right now

[Kframe]

Huh.  It's so weird.
Over on the website side of SOHC in the 550 section there are two road test articles from '73 and '74. 
One mentions that the mpg avg's 50, the other said 34-38.

Chain and sprockets new, tension correct to manual spec.
Tire pressure 30 and 32.  Wheel bearings , but, both wheels spin freely by hand when up in the air.

I suppose I should check timing, quality of spark, and sync again, probably the check air screw too (out 1.25 turns I think)?

Just don't know what these bikes are supposed to run like when dialed in, so I can't tell if I'm out of whack.
-K

[MCRider]

Huh.  It's so weird.
Over on the website side of SOHC in the 550 section there are two road test articles from '73 and '74. 
One mentions that the mpg avg's 50, the other said 34-38.

Chain and sprockets new, tension correct to manual spec.
Tire pressure 30 and 32.  Wheel bearings , but, both wheels spin freely by hand when up in the air.

I suppose I should check timing, quality of spark, and sync again, probably the check air screw too (out 1.25 turns I think)?

Just don't know what these bikes are supposed to run like when dialed in, so I can't tell if I'm out of whack.
-K

50 would sure be nice. On the test with 34-38, I wonder if there is a comment in the body of the test as to why so low.

Bearings can feel one way loaded and another unloaded. If more than 10,000 miles and/or 10 years, I'd put them on your list. The stockers were poor to begin with, and condensation cycles will expose them to a lot of water in the hub overtime. They were mostly sealed on one side only and replacements are mostly double sealed. Power washing will get in there as well.  But still they shouldn't make that much difference.

[Kframe]

The Cycle World article on this website reads:

You can expect, and get, instant starting, even idle, tireless revs, cleanliness, good manners, reliability, 38 mpg riding easy, 34 mpg riding hard and suitability to both city and highway.

My 550 has 21,??? miles, is a '74, and has sat in a garage in Minneapolis since 1985. 
So, I guess the bearing could be bad, but really, if the bike rolls around easily in the garage I can't imagine I've got too much drag in there, maybe could account for a mile or two-per-gallon...

Looks like I need to investigate further.
-K

[TedH]

I had a CB550F and it was normal to achieve mpg's in the mid 40's in city riding.  I've not had my 78 CB550K long enough to record mileage; still sorting out a dead #2 cylinder... about to rebuild that carb.

My '80 Yamaha 850 Midnight Special averages 40mpg as long as I don't ride hard; 30's with spirited riding.  It is in excellent tune and has shaft drive and full vindicator faring/lowers.

[Kframe]

Thanks, more info = a bigger sample = better info!

Yeah, I'd be shocked to actually get 50mpg, but I think, from what I'm reading, that I ought to be in the 40's somewhere.

Could slightly out timing at the points make this much of a difference?

Or should I be looking at a mixture issue?
-K

[TedH]

It can't hurt to ensure the carbs are synchronized/adjusted.  If you've had them apart and haven't, that will show benefit.  Also, setting timing where the timing is out of adjustment will improve fuel efficiency. 

How's the condition of your air filter?  If it is the old-style paper element and you either have no record of replacement or it looks soiled/old, it can't hurt to replace with a new element.

[Puntas13]

I'm getting 35mpg city 40mpg country out of my 500.

[cafe550]

last tank i got 50-55 mpg  74 cb550

[kck3]

I have a '77 cb550 with a 4 into 1 with 8200 miles on the clock and I avg around 43 mpg each time I fill up.

[Kframe]

Filter is Dennis Kirk's "OEM" replacement.  I would think OEM would mean a near identical paper filter, but it is a foam filter in a plastic box. 


I've bench sync'd my carbs, but don't have a reliable vacuum indicator currently.

Points have been static set, but I have no dwell meter to do a dynamic test.

I should look at the spark to check quality as well.

-K

[TwoTired]

My 74 Cb550 with stock exhaust and a Uni NU4055 air filter got 45 mpg or better.  And that's with a full Vetter Windjammer fairing on it.

The rest of my stock configured 550s get 45 or better, too.  I think the F models actually get better mileage.  But, I haven't actually measured it in a long while.

The above numbers were calculated when we could still get gas without alcohol in it.  It's probably 10% worse these days because of that.

If you are complaining about MPG, the first thing to do is review/verify all the tune up parameters.  And certainly, if the spark plugs don't show the same deposit patterns, something is certainly out of whack.

Cheers,

[the technological J]

two tired since your paying attn.... do u know anything about drilling extra holes in the emulsifiers?

[TwoTired]

two tired since your paying attn.... do u know anything about drilling extra holes in the emulsifiers?

Drilling holes in the emulsifiers and changing the size of the air jet will both effect mixture ratios.  (So will lowering the fuel level in the carb bowls.)
The position of the holes in the emulsifier also makes a difference, and where those holes are on the tube has an impact on what throttle position those extra holes have an impact.

If you are going to make a change, it is best to know at what throttle position you wish to effect a change. I.E. if your 3/4 throttle position is too rich and your 1/3 throttle position is just right, changing the entire range of mixtures to correct the 3/4 position is not recommended, as that will leave the 1/3 position too lean.

You need a throttle position fuel map to know where best to fine tune.  Or, a whole lot of plug chops under load conditions.

Then there is the matter of the barometric pressure variance the bike encounters.  The stock carb setting are not ideal under all conditions.  They are set so that wherever the bike is operated, the settings will never be too lean.

If your bike is operated routinely at 5000Ft altitude.  You could lean the bike out considerably without danger.  However, a carb tuned to operate optimally at 5000 Ft will be lean when operating at sea level.

This may be one reason why the mileage reports vary for the CB550.  My bikes are mostly operated near sea level.  I'm quite certain the mileage would be worse if I operated at a higher altitude.

Cheers,

[Kframe]

TT, thanks for the info.
I think a sync is in my immediate future, plus a second look at the timing.

In MN we can get gas w/o alcohol, it's 93 grade and on the pump there's a sticker saying it's to be used only in 'off-road' applications such as snowmobiles and ATV's, but of course people put it in cars and bikes, too.

I don't buy it for the octane, but for the non-oxy.
-K

[Fritz]

Thanks, more info = a bigger sample = better info!

Hi!

Just took some samples over the week end:

city: 34,3 mpg
highway, 70mph: 38,8 mpg
country roads, 60mph: 39,2 mpg

Bike is a '76 CB550F stock ingition, air box, carbs and exhaust - 20.000miles - wheel bearings new, tires inflated correctly and carbs just got a repair kit installed and synced - air screws tuned 'by book': 1 1/2 turns
I think the bike has been abused a lot by POs - consuming approx 0.5 quarts of oil every 1,000 miles but still pulls up to 8000rpms in 5th gear (~100mph)

[kayaker43]

I may have contributed to the old post on drilling emulsifiers but can't find it now. I was a dealer mechanic in the late 70's and that trick was being passed around. I think the source may have even been Honda through a newsletter or through their mechanics training schools.

Anyway I did it and got a solid 60 mpg on a 750 mile trip (75 CB550). It was all highway during the gas crisis so 55-60 mph ideal conditions. Still impressive since my buddy was riding a CB360 and we got the exact same mileage. Gas was only 60 cents a gallon then so I made the whole trip for $7.50. Those were the good old days!!!

I had a Hooker header and other jetting, and it was a new low mileage bike.

At the time there was no good explanation for why it worked. many people tried it and many people had results like mine, others less so?? I do believe that mixture in the 1/8 to 1/4 range is what determines your highway mileage because that's where you ride. The best theories at the time revolved around improved atomization more then leaner mixtures?

Anyway the mod was easy,.. drill extra holes the same size and in between the existing ones along the sides of the emulsifier. In otherwords, double the holes.

I have a different 550 now with 750 carbs, pods header etc. and it still gets 50 mpg. regularly.

[kayaker43]

Yes don't forget, ethanol decreases gas mileage,.. its not worth the 10 cents a gallon you save!!

[Kframe]

Yes don't forget, ethanol decreases gas mileage,.. its not worth the 10 cents a gallon you save!!

Yep, and that E85 is even worse!  Of course, that high % of ethanol would also eat our fuel system components I believe.
-K

[Gordon]

Yes don't forget, ethanol decreases gas mileage,.. its not worth the 10 cents a gallon you save!!

Yep, and that E85 is even worse!  Of course, that high % of ethanol would also eat our fuel system components I believe.
-K

I don't even know if a carbureted engine meant for regular gas would run on E85.  Never tried it though, and have no plans to.  If it did run it would be running extremely lean due to the oxygen in the ethanol.

[OrganDonor]

Just got through looking at mileage on my 77 550K.  This is about as stock a bike as you can get and the last two tanks got me 53 and 51mpg.  I wondered what was normal, so this thread answered it I guess.  In my case, little highway and mostly secondary roads.

[lone*X]

I always expected to see about 45 to 48 out of my 75 550K riding mostly highway miles.  In addition to tuning, a couple of factors to consider is throttle control and total weight.  A Big Boy will not get the mileage that a smaller person does.  Put on the pounds and mileage goes way down.

[Kframe]

I always expected to see about 45 to 48 out of my 75 550K riding mostly highway miles.  In addition to tuning, a couple of factors to consider is throttle control and total weight.  A Big Boy will not get the mileage that a smaller person does.  Put on the pounds and mileage goes way down.

Are you calling me fat?!?!

 

Just kidding.  With my gear on I'm about 190#. 

You're right about throttle control though, in my Bonneville which I ride pretty hard, I usually get about 42. 
Recently I rode with a buddy that rides more "nice" than I do, and I averaged 48 on that tank keeping pace with him. 

-K