Topic: Lousy gas mileage.........confused

[dylboss]

So, I'm trying to figure out why my gas mileage is so lousy.  '72 CB450 with 9k miles on it.  New plugs, carbs cleaned, runs great.  It seems that I need to throw on the reserve at anywhere from 110 - 128 miles.  That would be roughly 35-40 miles per gallon.  Shouldn't I be getting closer to 50?  My fuel/air screw is 1 turn out.  I should mention that I've also been adding 2 capfuls of Marvel Mystery Oil and 1 Oz. of Star Enzyme solution at each tank fill.

Thanks.

[super pasty white guy]

Here's some possiblities to start the conversation:
What do the plugs look like (sooty, tan, white)? 
Do you have a brake that's dragging at all? 
Is the air filter new?
How's the timing-  Did you do a full tune-up?

spwg

[tbpmusic]

A '72 would probably have 150 main jets (or thereabouts), so the mileage won't be as good as an earlier model in the first place.
Additionally, sub-par compression could contribute to less mpg. 164 psi is the minimum for a 450 - they will run ok at less than that, but a 450 with 180 psi or so would perform way better.

And stop with the gunk in your gas, it won't help anything at all. Just put in the highest octane gas you can find in your area..........

Observe the previous post's comments about checking the spark plug color.

[MoMo]

I have had many 450 twins-none now but to the best of my recollection that would be the normal mileage to switch to reserve. You have roughly 3 gallons on run and a half on reserve.  The mentioned checks from previous posters is all good info...Larry

[dylboss]

A '72 would probably have 150 main jets (or thereabouts), so the mileage won't be as good as an earlier model in the first place.
Additionally, sub-par compression could contribute to less mpg. 164 psi is the minimum for a 450 - they will run ok at less than that, but a 450 with 180 psi or so would perform way better.

And stop with the gunk in your gas, it won't help anything at all. Just put in the highest octane gas you can find in your area..........

Observe the previous post's comments about checking the spark plug color.

I was told that 87 octane should be fine.  Should I be putting in a higher octane?

[chickenman_26]

I was told that 87 octane should be fine.  Should I be putting in a higher octane?

No. If the bike runs fine on 87 with no signs of pinging, higher octane gas only serves to drain your wallet faster. It will not increase fuel mileage unless the bike was pinging/overheating on 87. Check your timing and other tune-up items.

Stu

[tbpmusic]

I was told that 87 octane should be fine.  Should I be putting in a higher octane?

No. If the bike runs fine on 87 with no signs of pinging, higher octane gas only serves to drain your wallet faster. It will not increase fuel mileage unless the bike was pinging/overheating on 87. Check your timing and other tune-up items.

Stu

Ah, the old high/low octane debate.
There's no clear answer to it. Though 95 octane is specified in the manual for 350's (and by extension for all the twins of that era), there are lots of arguments about how the ratings have or haven't changed, blah, blah.....

Not to argue with Stu, but don't take anyone's word for it (I didn't) - You just have to try it yourself - run a few tanks of high octane - if you don't feel the bike runs better, then don't use it.

All my bikes run better on higher octane, even my lawn tractor runs better on it.

[TwoTired]

I was told that 87 octane should be fine.  Should I be putting in a higher octane?

No. If the bike runs fine on 87 with no signs of pinging, higher octane gas only serves to drain your wallet faster. It will not increase fuel mileage unless the bike was pinging/overheating on 87. Check your timing and other tune-up items.

Agree completely.
The energy content of all pump grades is the same.  It is the additives/formulation of the fuel that effect what temperature it ignites, and to a degree, how fast the flame front can spread in the chamber.  Higher octane fuels take more heat to spontaneously combust.

Feelings really have very little direct connection to measured performance.  It is precisely why double blind testing was developed.  Marketing persons hate scientific testing, as it eliminates any manipulation of human baser instincts.

Cheers,

[chickenman_26]

Ah, the old high/low octane debate. There's no clear answer to it. Though 95 octane is specified in the manual for 350's (and by extension for all the twins of that era), there are lots of arguments about how the ratings have or haven't changed, blah, blah.....

Bill,
Clear and factual answers are easy enough to come by. Debate is usually between those who confuse opinion for fact. The 95 octane rating in the '70s was arrived at using the Research Octane Number (RON) which is still used today in most countries. There's another test method referred to as the Motor Octane test that stresses the fuel to simulate how it compares to a reference fuel under load and high temperature. Motor Octane numbers (MON) with that test are typically lower than RON. Motor fuels in the US today are rated using the average of their RON plus MON numbers and reported as Road Octane, Pump Octane, or Anti-Knock Index.  That 95 octane "regular" fuel of the '70s had a MON of around 80. So today's 87 performs virtually the same. (95+80)/2 = 87.5. You'll find that math formula - (R+M)/2 -  posted on almost all gas pumps in the US.
More on this if you're interested
http://www.astm.org/Standards/D2700.htm
http://www.astm.org/Standards/D2699.htm

Stu

[dylboss]

Very interesting stuff.  Thanks to all for chiming in.  I haven't done anything with the timing, because the bike has been running so good.  Idles fine.  I guess I'll stick with the 87 octane, since that seems to be the consensus.

[chickenman_26]

I haven't done anything with the timing, because the bike has been running so good.  Idles fine.

You might want to check it, given your fuel mileage complaint. As the points' rubbing blocks wear, the timing becomes retarded. The bike would likely still run well, but fuel mileage would suffer. Better to know than not know...

Stu

[dylboss]

I haven't done anything with the timing, because the bike has been running so good.  Idles fine.

You might want to check it, given your fuel mileage complaint. As the points' rubbing blocks wear, the timing becomes retarded. The bike would likely still run well, but fuel mileage would suffer. Better to know than not know...

Stu

Good thought.  I'll tear it apart in the next few days.  Thanks.

[tbpmusic]

Yeah, I've read all that stuff for years, Stu.
Again, I don't base too much of what I do on what other people say, no matter how smart they might be (or not). Not that I ignore them, but I have to prove things for myself, that's just who I am.
My bikes simply run better on higher octane, it's easy enough for me to perceive.......if I didn't notice a difference I wouldn't use it. (Anyone wonder if folks like Team Hansen run 87 octane in their 450's??)

Subjective - won't deny that. Nearly everything about our old rides is subjective, right down to the way we want them to look - witness the current incarnation of the cafe craze, which my generation got tired of in the '60's.
If I based what I do on the "expert's" opinions and stuff off the internet, I'd be riding a whiz-bang new bike, not a totally obsolete, 40+ year old, maddeningly fickle POS.

Just shows that all of us who mess with these old bikes pretty much have a screw loose somewhere - but you and I have known that for a long time, no??

With that then, I'll bid you all adieu......

[chickenman_26]

(Anyone wonder if folks like Team Hansen run 87 octane in their 450's??)

If they don't use it on the race track, then it must not be best for the street? By all means Bill, "prove" it to yourself and do as you like. But don't offer that argument to bolster your conclusions. I doubt Hansen is running stock compression, cam timing, ignition timing, gearing, or stock anything else. To extrapolate a street bike's needs from those of a race team doesn't make logical sense. It makes plenty of emotional sense, though.   

Stu

[TwoTired]

Back in the 60's/70's many major car manufacturers backed stock car race teams.  They even made special "production runs" of stripped down beefed up cars, to be sold or donated to the teams prominently display the brand badge.

The idea/campaign, which was quite successful, was "Win on race day, Sell on Monday".
Whichever brand won the weekend race would see a sales boost of the winning brand afterward.  It didn't matter that the cars were hugely different under the skin.  It was the badge being sold to all that wanted to be associated with a winner.  They were selling self esteem, not any technical superiority.  Marketeers have learned to sell toward human emotions.  Everybody has those.  Not everybody has the skill, knowledge, or interest in the accurate evaluation of every product they buy.  So, the good consumers buy/bet on what the winners buy/bet on.

Personally, I find such manipulative practices despicable, despite being pervasive and a major component of today's media.

HAPPY THOUGHTS!