So I checked fuel consumption after a ride this week and wearing a leather jacket versus mesh and running 87 octane instead of premium, I bumped my mpg to 36 from 33. Not too bad.

I still think my a/f mixture is a bit rich. So the story continues............

 

Widebands don't serve their purpose if you have smig pumps or pair or cats in the exhaust or anything else that will alter the A/F ratio leaving the header.

Most car guys weld a bung into the header Y pipe and install the wideband sensor there.

 

Aha! So we found the problem. I wonder what my MPG's were with a passenger at full speed. I didn't pay attention.

 

Good thread.

What CentralCoaster is describing are "pumping losses".

Being in a taller gear causes the engine to spin slower, so you run with a more open throttle position to get the same mass flow rate of air through the engine, which is a requirement for the same power output, given optimum combustion.

A wider throttle position gives better volumetric efficiency, which is a measure of the amount of air at ambient pressure that enters the cylinder in a cycle. If the throttle is closed ,the VE is low.

A good example of this can be seen in a low-powered car going uphill. If you keep it in 4th, with the throttle wide open and the car just maintains speed, then downshift with the throttle wide open the engine flows more air, which makes more power and the car accelerates.

Running with an open throttle improves VE and MPG. But if you want to accelerate, you need to be in a gear that requires a lower throttle position to maintain a constant speed. Then the increased VE when you open the throttle will cause a higher mass flow, for more power.

Not sure what it has to do with Reaper's MPG though...

 

BS... you weigh at least 100 lbs. more than me!

Funny thing is my bike has over 50,000 miles, original air filter (did vacuum it one time), street baffle Jardines w/o jet kit. I did replace the plugs once, but that's it for tune up. Sometimes less is more I guess.

 

Hah! that's awesome. You mean the factory guys know what their doing with all of that refinement and development?

I'd like to ride a motorcycle some day.

 

Rode about 250 miles yesterday and still averaged 36 mpg through the mountains and highways.

Today I adjusted the tps from 900 to 500 and changed my a/f mixture to 2 turns out from 2 1/2 turns.

The throttle seems to be snappier. Plan to ride tomorrow and see how she performs.

 

FWIW, I averaged about 45 mpg on the highway sections coming back from Death Valley, with 40+ lbs worth of luggage and saddlebags to ruin the aerodynamics. And with a head wind on some of it.

Speedo registered 71 mph on a radar sign that read 73, so I guess the mpg would be accurate also.

 

CC I weigh in at 250# w/o gear.

 

There's a big guy in my riding group on a 02 Hawk. Next time I see him I'll ask what mileage he gets. He looks like a gorilla mounting a tricycle when he's on it. Actually he's a member here, I should watch my language!

I weigh about 125. Makes the gokart faster too.

Next time I do a distance ride with my g/f on the back, I'll post my mileage, but she usually takes her bike for long trips.

 

Well I pulled the carbs off this week and adjusted the tps from 900 to 500 and set the a/f mixture screws at 2 turns from 2 1/2 turns and boy what a difference it made in the performance and throttle response.

The weather has been wet since so I have not had a opportunity to put some miles on the bike to see if my mpg has increased/decreased. Will follow-up later.

 

My Hawk is -1 front +2 rear with Graves Slip-ons (sound awesome) Up'd the pilots a couple sizes, been so long Im not sure what it was, a 190/50 tire with 36psi cold 38psi cold front. now for the good part. Just cruising around town with the occasional throttle snap here and there I got ahh to be conservative 35-38 MPG. Now I found some 93 Octane fuel where I live with NO ETHANOL so I thought what the hell. I beat the living dammitt outta my baby going from Athens to Englewood up hwy39 to 310, over to hwy 64 the 68 into Tellico this past Sunday. I ran 112 miles so as we all know its not long before a refill. Well I just about fell over when it held only 2.636 gallons (thats 42 MPG riding VERY VERY hard) I am 6'4 and 265lbs Oh and if the guys I passed in the corners on 310 are on here no hard feelins huh ...VRooooom. Hard to beat engine braking.
The moral of this story is find some Ethanol FREE fuel any octane and fill completely up with it. See if you get the same results. I've beat mine up around town and got apprx 32MPG So thats something to think about.

 

I still battle a lean condition too. I have to pull my choke out about 1/4 to 1/2 inch for it to run smooth and not feel like its always running into a strong headwind. Any suggestions to fix that? I have a spare carb set so i dont mind experimenting

 

35-40 MPG? I'm doing between 22-29 MPG on my Hawk
(96-124 miles a tank, 4,22 gallon tank)
Is something awfully wrong with my bike? :S

 

Are you actually putting in 4.22 gallons? My bike is pretty fat on the pilot jet which hurts the economy, but I'm still getting 36-37mpg pretty much every tank. This morning it was 139 miles and 3.8 gallons.

 

in town I drop just below 30 mpg, but usually on the highway and on normal rides I get 40mpg to 45mpg. So it can vary alot.

 

Worst I've gotten is 36 and that was hittin' the throttle pretty well, but when I ease around and don't crank too hard, I get up to 45 mpg. Oh yeah, I weigh 235#, too.

 

Yeah, I actually ran empty 96 miles after full tank once, driving a bit hard, with a passenger, but anyway, isn't that way too much? So that's about 22 mpg. 16/43 gearing, MIG-exhaust, it may be running a bit rich, some popping from the exhaust. Could a rejet solve the problem?

 

Can I Squeeze Anymore MPG?


you bought the wrong bike and / or are on the wrong site

 

A quick comment on octane, it is simply a waste of money to run premium fuel unless you have increased the compression in your cylinders. Higher octane fuels were developed to withstand knocking at high cylinder pressures. Unless your bike is knocking, you can use regular fuel. And if your bike IS knocking, it's probably a broken engine part, not low-octane fuel.

"The octane rating is a measure of the resistance of gasoline and other fuels to detonation (engine knocking) in spark-ignition internal combustion engines. High-performance engines typically have higher compression ratios and are therefore more prone to detonation, so they require higher octane fuel. A lower-performance engine will not generally perform better with high-octane fuel, since the compression ratio is fixed by the engine design." http://en.wikipedia.org/wiki/Octane_rating

 

Sure, but would you not agree that a VTR engine is a "high-performance" engine? It's wipes it butt with car engines in all categories including hp/displacement. Let's not forget how far it revs, albeit low for a motorcycle engine but higher than car engines. The details you reference are either 1) general facts about how octane is defined or 2) based mostly on automotive engines.

Blindly quoting some pieces of information and drawing a broad conclusion is dangerous.

 

For 13 years my SuperHawk has delivered about 37 MPG- regardless of brand or octane. But with Shells new "Nitrogen Enhanced" fuels my mileage has steadily increased with each successive fill-up. Climbed to 39 MPG, next tank was over 42 MPG, and most recent fill-up netted 43.67 MPG. NO mechanical changes like valve adjustment, carb synch, dropped needles, fresh plugs, lower restriction air filter, low viscosity oil, increased tire pressure, etc. I'd normally call claims of "Nitrogen Enhanced" nothing more than marketing BS but my results show that someting is definitely changed in Shells fuels.

 

Depends what your comparing it to.....We can compare this to a big cat engine, an outboard motor, or even a tractor motor.


Well said Jamie

 

"High-performance engines typically have higher compression ratios and are therefore more prone to detonation, so they require higher octane fuel."

Who are you arguing with?

It said typically. Motorcycles typically have 4 cylinders, the Hawk doesn't have that either.

Misrepresenting truthful information is dangerous too.

 

"Blindly quoting some pieces of information and drawing a broad conclusion is dangerous."

Excuse me. Before you suggest that someone is "blindly quoting information" and drawing "dangerous conclusions", you might want to do a little research. The Superhawk engine is far from a "high performance engine" by engineering standards. Compression ratio on the Superhawk is a very mild 9.4:1, unless you've done something to increase yours. A high compression ratio is typically in the range of 12-13:1.

I am an FAA certified mechanic. Octane ratings are particularly important in aviation engines because they run at near full throttle, nearly all the time, so there is much more risk of detonation than in our engines that are loping along at 3-4000 RPM for most of their lives. Octane ratings are something we studied in school.

I was not "blindly quoting information", I was attempting to do a service to the members of this group (which will save you about 10% on fuel costs = more riding) by pointing out what every engineer knows -- excess octane is a flat out waste of money. I quoted a source just so that it would not appear that I was simply posting a personal opinion (as so many others have done). It's not a personal opinion it is scientific fact. If you disagree, how about quoting some sources rather than suggesting the poster doesn't know what they're talking about??

 

I think he knows the Hawk doesn't need high octane but is just arguing for the sake of arguing. Which I find quite annoying and unnecessary.

 

If you read my posts earlier in this thread I think the VTR does need premium fuel. It was a big difference on my bike, which is mildly modified internally with [basically] stock compression. 9.5:1 compression is pretty decent and certainly is not "low".

What is "annoying and unnecessary", as you put it, is when people point to generic sources and completely different types of engines and draw a conclusion back the VTR. These are not deisels, turbocharged, rotary, or turbine engines.

Since it was asked, I'm a graduate level educated and degreed Mechanical Engineer from Purdue University, in case those credentials mean anything to anyone. I don't think it takes higher education to understand that a rough running, poor performing engine on 87 octane that runs great on 93 octane should have premium fuel all of the time.

 

I wanted to let this go, but since you are an engineer, I'll make one more attempt. Here is another link to an excellent article on fuel, compression and detonation, written by a General Motors engineer about car engines. The article was published in an aviation magazine. The basics of engines are the same across vehicles. And no, 9.5:1 is not considered a high compression ratio by any scientific measure. If you want to consider it a high ratio, as compared to a lawnmower say, then that's great for you. But before you "draw broad conclusions", I think you should go back to your textbooks and base your conclusions on science rather than a seat-of-the pants-dyno.

Of course, perhaps there is some reason why your particular engine runs better on higher octane. Perhaps you have excessive carbon build-up that is impacting the size and shape of the combustion chamber. Or you've advanced your ignition timing such that you need the faster burning fuel. Or the carbon build-up is causing hot spots that detonate with slower burning fuel. But your engine is definitely an exception to the standard, published, much-documented standards for octane and compression ratios, regardless of what chassis they're installed in.

P.S. Go Boilermakers!

I'm done debating, in case anyone else wants the last word...

 

No it doesn't mean anything. I'm a degreed and licensed professional mechanical engineer, but I don't expect you to believe me if I say the sky is purple.

Your personal recommendation differs from Honda's engineers and that of many other SH riders. Maybe your bike is the exception. Maybe the combustion chambers are full of carbon buildup, maybe the knock resistance of the premium is compensating for something else that isn't running in proper tune. You never said anything in this thread referencing premium fuel until now, so I apologize for assuming you were arguing for the sake of it.

Anyhow, I'd be curious to hear your thoughts on why my bike runs great on the factory recommended 87 octane with 34,000 miles on the clock and also averages 15% better fuel economy than yours.

(Fuel economy is the topic of the thread.)

 

A lot of what Jamie referenced was covered in another thread specificly about octane and it's effects on the VTR... And with his particular setup to his engine, it does like higher octane, for whatever reason... (I can't remember which thread that was though)

But I'll say the same thing I said there... I'll bet my bike that you can take Jamie's bike or any else and set it up to run very well on 87, with excellent mileage, and it's be a bit unhappy and thirsty on 93... Then tear it apart and re-do it for 93 and it's going to exhibit the same thirsty, rough running on 87...

These bikes are carbed, with a huge carb that probably is a bit oversized for the application... That has caused more than one engine tuner to scratch his head...

The thing with a carbed bike is... You set it up for the humidity/height over sea level and fuel that's in the tank at the time you tune it... It's that simple...