Average MPG for 71 CB500/4 K? How to optimize?

[edelweiss]

I looked on fuely.com and saw the average MPG for the CB500 varies quite a bit. I know this depends on how and where you ride (local/highway, fast/cruise)

1. Is there any basic ways to insure I'm getting the best MPG on my bike?
2. How does a Carpy's 4 into 1 exhaust effect my MPG — better or worse MPG?

Thanks!

John

 

[Big R]

Well, there's a lot that goes into MPG.

Assuming that the engine is performing at its finest (as in "maintenance"), a light throttle hand will get you the best economy. Punching the throttle, leaky carbs, ancient wiring, rusty as heck chain, etc, will all kill fuel economy.

For what it's worth, I watch my MPG as well. Not because I like to brag about saving money, but because if I have a sudden drop in fuel economy it means that something isn't functioning properly.

 

[SONICJK]

Stay out of the throttle 8)
My 400f gets around 45 just cruising with a relatively heavy wrist, and it can drop significantly if im full throttle all the time.
Ive never babied it to see what it "can" do.
I drive a jeep on 37's and a diesel truck, so 45 is astounding to me

 

[edelweiss]

Thanks guys. Reason I asked is that I ride my 71 to and from work of course for the great feeling, but also to save gas because my 2013 Tacoma pickup costs $80 in gas a week.

Each way is 37 miles and I go the speed of traffic which is around 70 MPH at 6,000 RPMs. I have not calculated my MPG, but will very soon.

Will a 4 into 1 exhaust lower or higher MPG or have no effect?

Thanks!

 

[SONICJK]

Would probably increase mileage and free up a little power if you jet for it, coming from the stock exhaust i assume?

 

[edelweiss]

Yes, I have a Carpy's 4 into 1 exhaust still in the box and bought 130 and 135 jets to see which one works best. They suggested a 130. Eventually I would like to put pods on as well. How do pods effect the MPG?

 

[SONICJK]

Anything that frees up airflow in or out should increase MPG theoretically. In the real world I couldnt tell ya.

 

[Big R]

Technically, putting in larger jets will flow more gas, which will hurt your MPG. Significantly? No. You might go from 40 MPG to 39.5 MPG. And the exhaust alone will have a far lesser effect on fuel economy than exhaust w/ pods. Only because changing the intake has a more dramatic effect on your air / fuel mixture.

What it boils down to is that your right hand will make or break your fuel economy.

 

[SONICJK]

Technically, putting in larger jets will flow more gas, which will hurt your MPG. Significantly? No. You might go from 40 MPG to 39.5 MPG. And the exhaust alone will have a far lesser effect on fuel economy than exhaust w/ pods. Only because changing the intake has a more dramatic effect on your air / fuel mixture.

What it boils down to is that your right hand will make or break your fuel economy.

Rich true it flows more gas, but in theory you should be able to maintain speed with a lower throttle opening since you pick up a couple ponies, increasing mileage.
It's probably a wash though in the end.

 

[Big R]

Justin, you're right too. I've noticed that larger bikes from the same era as my GS450 get the same mileage (on average of course). I chalked it up to "larger motor = more power = not struggling to maintain speed".

Oddly enough though, while I get around 50 MPG, folks that have GS500's are capable of getting 60-65 on a regular basis. But that's a whole other discussion .....

 

[edelweiss]

Cool, thanks guys!

 

[surffly]

Would assume best MPG on a well maintained stock bike.
The small increase in power will not let you cruise at a lower RPM or save fuel.
The increase in jet size will flow more fuel to balance the better air flow and decrease MPG.
Bad mods like pod filters will decrease MPG because of poor tuning.

Who said 130 jets?
Whats stock in a 500? if anything like a 550 a 130 is huge

 

[edelweiss]

Would assume best MPG on a well maintained stock bike.
The small increase in power will not let you cruise at a lower RPM or save fuel.
The increase in jet size will flow more fuel to balance the better air flow and decrease MPG.
Bad mods like pod filters will decrease MPG because of poor tuning.

Who said 130 jets?
Whats stock in a 500? if anything like a 550 a 130 is huge

A guy at Carpy's said 130 for the 4 into 1 exhaust they sell. I believe the stock jet is 110 on a CB500/4.

 

[Catbird]

If you're interested in upping your economy and dropping your revs, as well as increasing theoretical top speed, nothing like a gear change. Add a tooth or two to the front and knock three or four off the back. Less neck-snapping acceleration, but having power in a better place is great at highway speed if you've got an emergency and need to pass.

Unfortunately the timing stuff is trickier to do on fours(well, easier, but more expensive) than on two-strokes, which you can do with a metal file and a dry paintbrush if you're clever enough and know exactly what to do, and in the right place, stretching or changing the ports in a two (equivalent to changing the cam in a four) can improve your mileage and economy, though while your bike might make an extra 4 horsepower and get an extra 20mpg, it will not do the two at the same time.

Optimize *your* mileage with a half-fairing, a good aerodynamic helmet, a full-tuck riding style whenever you're cruising at speed, keeping your tires inflated to their maximum pressure, keeping everything oiled and tensioned just right, and maybe a gear change.

I've got a dorky little DT250B that I love to death, but at 21hp, it should do better than 48mpg. I'll be swapping some stuff around this coming week.

 

[bradj]

If you knew what a hot rd motor goes through in fuel and oil, you would behappy with whatever your honda mpg is

 

[SONICJK]

If you knew what a hot rd motor goes through in fuel and oil, you would behappy with whatever your honda mpg is

Yeah when i was looking into 2 strokes hopped up RD's seemed to be getting around what 18mpg? hahaha

 

[edelweiss]

Yeesh!

 

[bradj]

Yeah when i was looking into 2 strokes hopped up RD's seemed to be getting around what 18mpg? hahaha

mabie 18, then you gotta factor in the price of spectro.
to mix 5 gallons of fuel when gas was high all said and done is around 40 or 45 bucks with a 4 gallon tank it is a pain in the ass buuuut its fast as fuck

 

[Catbird]

My dad used to claim after the 7th-port job and an RZ piston and some gearing change, it was mild enough that if he stayed out of the power band he'd get close to 100mpg out of his '75 RD350. But that's hard to say... Much as I respect the old man, he was born and raised in the south, and that means he carries the dominant hyperbole gene.

That, and it's entirely possible that his bike was geared so strangely that it was actually possible to ride it outside of the allegedly paper-thin powerband.

I know my DT250 isn't where I'd like it to be. Maybe after I replace the driveline stuff that got all munched up by my negligence with the chain...

 

[SONICJK]

Would assume best MPG on a well maintained stock bike.
The small increase in power will not let you cruise at a lower RPM or save fuel.
The increase in jet size will flow more fuel to balance the better air flow and decrease MPG.
Bad mods like pod filters will decrease MPG because of poor tuning.

Who said 130 jets?
Whats stock in a 500? if anything like a 550 a 130 is huge

RPM wouldn't change at speed regardless of power increase, thats all gearing.
more power less throttle (think how you have to use less throttle to maintain the same speed if you tuck) .
Yes its probably negligible but were talking in theory here.


Look at any car (where people care a lot more about MPG) the addition of a cold air intake and a decent exhaust always translates to an increase in mileage as long as you keep your foot out of it.