Topic: Gas Mileage

[super pasty white guy]

Cause I've got too much time on my hands this morning, I got curious about how all the bikes stack up.
I tried to eliminate people who posted their mpg several times, but I probably missed a couple.


And, if you want to roll your eyes and call me a nerd, go ahead.  I'm used to it.

Dave

[Gordon]

That's great!  And very much in keeping with your forum name.

[Pinhead]

After changing my jets it was running a bit rich, so I took off the air filter cover and drilled my exhaust slightly. Now I'm getting 50mpg. 1979 CB650.

[nickjtc]

Cause I've got too much time on my hands this morning, I got curious about how all the bikes stack up.
I tried to eliminate people who posted their mpg several times, but I probably missed a couple.
And, if you want to roll your eyes and call me a nerd, go ahead.  I'm used to it.
Dave

Thanks for doing that, Dave. So in this bit of research it looks like us 650 riders are the winners in the 'bigger' motor sized category. Yay!

[tsp37]

Put another 650 down for 58 mpg in the heat of summer, 51 in the cool of spring, and 2006 average of 54 mpg.  That's conservative commuting (around the 50 mph sweet spot) and a rare ride with gusto on the weekend.

[kayaker43]

I was a Honda mechanic in the 70's and there was a popular modification being passed around that increased mileage. I had a CB550 with hooker header, filter pods and jetting. I typically got 45-50 mpg.

The trick was to remove the emulsifier tube (long tube with holes in the side, that surrounds the needle) and drill more holes in it. I was told but never confirmed that this was reported in a Honda "Tech Bulletin". Without firm details, I was told to drill new holes the same diameter and between the existing ones, thus doubling the holes. The emulsifier tube is where air mixes with fuel drawn through the main jet and around the needle so it enters the carb as more of a foam than liquid. The modification was said to improve atomization and have no effect on fuel metering (no change in jetting).

It was easy and cheap so I tried it right before a 750 mile trip. My buddy was riding a CB360 and we each got 60 MPG. I was amazed that I could match his fuel efficiency and there was no change in performance like cold blooded starts when running too lean. The plugs looked the same as they always did. I never repeated the test or heard feedback from others and wondered if it really worked for other bikes, or just fixed some deficiency in 550's??

60 MPG and gas was 60 cents a gallon,.. that's a penny per mile!!  The whole trip cost $7.50 for fuel,.. I recently did an 850 mile dual sport ride on my XR650 and spent over $100 for fuel 

[Pinhead]

Well, we'll see. I'm going to go do it to my 650 right now.

Hondaman does a mod that simply bores out the top two rows of holes to a slightly larger size. I wonder if they end up doing the same thing...

[Buber]

can you be so kind as to post some pictures? Like which place exactly to bore those holes? Y'know, in Europe fuel is just a tad more expensive than in US, and anything to improve that helps....   

Thanks in advance...

And BTW - does anybody have a decent CV carbs manual? I do have service manual for my CB 650, but it's for the old carbs, and I have the CV ones...

Thanks again 

[Pinhead]

can you be so kind as to post some pictures? Like which place exactly to bore those holes? Y'know, in Europe fuel is just a tad more expensive than in US, and anything to improve that helps....   

Thanks in advance...

http://www.sohc4.us/forums/index.php?topic=10990.0

And BTW - does anybody have a decent CV carbs manual? I do have service manual for my CB 650, but it's for the old carbs, and I have the CV ones...

Thanks again 

http://www.cryscom.nb.ca/PDF_Docs/Honda_Technical.pdf

[Buber]

And this is why this forum is so GREAT!

Thanks!!!

[super pasty white guy]

Since riding season is upon us and the gas prices are rising again, I thought I'd post an update and rejuvenate this old thread.

Last year I was getting 35-36 mpg on my '76 750F. 

After going with iridium plugs and a Uni foam airfilter this spring, I've been up to 39-40 mpg.

dave

[c_kyle]

My '79 650 gets around 33mpg with 50% City driving and %50 Highway.

[Gordon]

One interesting thing I've noticed through some experimentation over the past couple of years is that my 750 gets 40-42mgp in the city no matter how I treat it.  I've tried taking it easy on the throttle to see if it will increas the fuel economy, but it still gets the exact same mileage as when I tear away from every stop sign or red light.

[Bob Wessner]

Sounds like very little reward for good behaviour, so what the heck..

[Gordon]

Sounds like very little reward for good behaviour, so what the heck..

My thoughts, exactly!  

[moduleum]

Hmm... I think my 650's running a little lean... I get 57-60 mpg all day long.

When I fixed my alternator my mileage went from 60 to 40. Now that's one hell of a drop! I ran it that way for a while, but after I ran it out of gas a couple of times I disconnected the alternator again (and all of the fuses to keep my battery from running down) and I'm back up to the 60mpg figure. It had more top-end power and a little more mid-throttle response, but around 3000rpm (where I normally drive) it runs just as good, if not better without the alternator. Why in the hell would the alternator pull my engine so much???

Can someone follow up on this?  Is there any merit or a solution to this?

[merc2dogs]

 Don't know on the 750, but do know from experience that a 35 amp GM alternator will stall a 3 horse gas engine running flat out when a heavy load is applied to it.

 one common mod for performance cars was to install a switch on the alternator to turn it off for a race. Some people claimed a 15horse gain.

ken

[OldSchool_IsCool]

By turning it off, you mean switching off the field coil, right?  That would be the white rectifier wire or green ground wire and not any of the yellows three-phase wires, eh?

[batdan]

 Don't know on the 750, but do know from experience that a 35 amp GM alternator will stall a 3 horse gas engine running flat out when a heavy load is applied to it.

 one common mod for performance cars was to install a switch on the alternator to turn it off for a race. Some people claimed a 15horse gain.

ken

15 hp is about 11,000 watts. The cb750 alternator is rated at 210 watts at 5000 rpm, which is less than 1/3 hp. There are probably others losses associated with the rectifiers and whatnot, but I doubt it adds up to even 1 hp on the cb750 at maximum current draw. The drag from the alternator is proportional to the current you are drawing from it, and during the day you don't have your headlight on or anything so the alternator is only running the ignition and occasionally turn signals which isn't too much anyway. It's probably not worth the effort to disconnect the charging system. Also your battery would discharge and you'd have to recharge it anyway.

[merc2dogs]

whatever wire turns on the field.

 I agree, the battery needs to be charged, as it loses charge, you lose performance.

  never did agree with the 15 horse claims, but no solid backup for or against.
it does take power, but 210 watts can't pull too much.


Ken

[ofreen]

My R100GS has heated grips and I have noticed up to a 5 MPG or more drop in fuel mileage when using them for an extended time.  I have noticed the same thing when running an electric vest.

[Pinhead]

I drive a '79 CB650. I removed the air filter cover, replaced my 90 mains with 102.5's, got a 1 tooth larger front sprocket (17T, 40R), removed the rear baffles off of my mufflers, and side-gapped my spark plugs. I'm now getting 65mpg US (3,6l/100km) driving around town.

[UnCrash]

   On a recent run up to Owls Head I got right around 50 mpg on my 78 750F3

[steam-powered man]

after my camchain sprocket bolt mishap, found a great replacement motor (low miles, great compression results) and am getting 52 - 55mpg all the time.  cleaned and set the carbs per this fine board, set the valves and point gap per the manual, and away i went.  plugs look perfect.  i take it easy on the old girl, usually shifting at 4 -5K, rarely at and never above 7k.

am liking this bike.
bobp

   

[kpier883]

I put in a new air filter and changed the idle jets (#40 to #35) to leaner and picked up maybe two or three mpg.  I was getting 29 - 32 mpg before and maybe 31 - 35 mpg now. 

I don't like to change too many things at once because then I wouldn't know which change caused a potential problem. 

I have some #105 mains that will be replacing the #110 currently in it soon, and hope to improve my mileage some more.  I have noticed that when I really give it some throttle, it will billow black smoke.  Already lowered the needles and it helped but didn't eliminate the smoke.  Also notice that at wot I get less acceleration than at 7/8 throttle and I think it is due to being rich.