Author Topic: increase gas mileage  (Read 3761 times)

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Offline dl52163

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increase gas mileage
« on: March 14, 2011, 07:49:53 PM »
OK I have read the stuff hear and I am embarrassed to say I am only getting 30-31 MPG. Any thoughts on how to increase the MPG.
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Offline Gman

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Re: increase gas mileage
« Reply #1 on: March 14, 2011, 07:53:02 PM »
Walk.   ;D 


Sorry - couldn't resist.
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Offline kpier883

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Re: increase gas mileage
« Reply #2 on: March 14, 2011, 08:37:55 PM »
OK I have read the stuff hear and I am embarrassed to say I am only getting 30-31 MPG. Any thoughts on how to increase the MPG.

What year and model bike, and what modifications if any have been made?

I get 40 + with my '74 CB750 - stock except for some aftermarket mufflers (2) and a Dyna ignition.  Running #105 mains and #35 idle jets, but don't remember the needle setting.
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Offline dl52163

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Re: increase gas mileage
« Reply #3 on: March 17, 2011, 09:30:58 AM »
OOPS some more information would have been helpful. 1976 CB 750 F that is stock. I have had the carbs rebuilt and they are currently at the stock settings according to the manuals.
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Offline RedDawn

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Re: increase gas mileage
« Reply #4 on: March 18, 2011, 08:42:40 AM »
What sprockets are on the bike and how fast do you ride?
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Offline dl52163

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Re: increase gas mileage
« Reply #5 on: March 22, 2011, 11:16:39 AM »
Stock and I ride a lot of freeway and some around town. I do spend more time on the freeway though
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Offline TwoTired

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Re: increase gas mileage
« Reply #6 on: March 22, 2011, 11:50:09 AM »
Have you replaced the air filter...ever?

Tried a K&N air filter?

Have you checked your spark plug deposits  (all four)?  Do they all show the same deposit pattern?   What color?

Are you using Ethanol fuel?

Have you ever cleaned the emulsion tubes in the carbs?

Have you checked the fuel level in the carb bowls?
Lloyd... (SOHC4 #11 Original Mail List)
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Offline Bakeoff

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Re: increase gas mileage
« Reply #7 on: March 22, 2011, 12:12:41 PM »
The only thing I think he missed is ignition timing.

Offline dl52163

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Re: increase gas mileage
« Reply #8 on: March 23, 2011, 04:07:40 AM »
Timing is good and we are replacing it with a electronic ignition in a couple of weeks. We have had to adjust the current timing about every 2500 miles currently. this is the reason for the upgrade.

Air filter has been replaced and will be upgrading to K and N filter soon.

Can not tell you the color but plugs have been changed and according to the mechanic they are looking great. We had to change them and make two of them different due to the way they were burning and looking.

What other fuel is there? All or I should say just about all fuel has ethanol and I really do not know what to do. I run octane buster and carb enzyme through it to get the best response I possibly can.

Emulsion tubes and everything has been super cleaned as well as most of it has been replaced. Not the tubes, but they have been cleaned several times.

Floats had to be adjusted to get rid of a stumble we were having in the lower idle range. It is about gone but still a little tricky when cruising down the interstate. They are adjusted 2 mm beyond stock settings.

Currently to get the best performance I can fill up with premium gas and add a bottle of octane boost and about 1/2 bottle of fuel enzyme to the tank and I will get in the 35-37 MPG on my daily run. This winds up being close to 4.50 per gallon once you calculate everything together. Granted I am still saving money riding the bike compared to my truck but to get maximum performance it gets costly.

What do you do and what are your specific settings to get good gas mileage?
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Offline MasterChief750

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Re: increase gas mileage
« Reply #9 on: March 23, 2011, 07:12:14 AM »
what octane are you running. the booster is not needed and i believe that the booster is a bunch of bologna. mythbusters debunked that stuff on an episode. the user manual calls for 91 octane but that was in the 70s when, someone correct me if im wrong, the US used the RON octane rating. the octane rating system in the US now is the anti knock index. whick equates to 87 octane compared to the 91 of the 70s. just a thought.
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Offline dl52163

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Re: increase gas mileage
« Reply #10 on: March 23, 2011, 07:17:41 AM »
premium which is 93 octane. Now I was at Road Atlanta one weekend and filled up with 105 octane race fuel and I could tell the minute it hit the carbs. Different sound in the engine and ride was awesome. 9.00 something a gallon is a bit steep for my daily ride.
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Offline MasterChief750

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Re: increase gas mileage
« Reply #11 on: March 23, 2011, 07:32:08 AM »
i usually run the highest octane available as well premium is usually 93 around home, 94 if i go to sunoco, premium is 91 in michigan i have found so ill run that. my bike runs just as well on 89 but on regular 87 it will tend to skip a beat and mileage goes down. do some testing for yourself, run a tank of each grade and see which one gives you the best price per mile, not just mpg. you will find what saves you the most money.
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Offline TwoTired

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Re: increase gas mileage
« Reply #12 on: March 23, 2011, 10:44:46 AM »
Can not tell you the color but plugs have been changed and according to the mechanic they are looking great. We had to change them and make two of them different due to the way they were burning and looking.
No way should you need to change plug types across the bank to make it run properly on all cylinders.  This makes me question your mechanics opinion of "looking great".

What other fuel is there? All or I should say just about all fuel has ethanol and I really do not know what to do. I run octane buster and carb enzyme through it to get the best response I possibly can.
It just that ethanol fuel with provide worse mileage that pure gas.  It a mater of expectations.  I would expect a 750 to get about 45 MPG or better on real gas, but 10-15% worse on ethanol blended fuel.  You can thank your elected officials for sabotaging your gas.

Emulsion tubes and everything has been super cleaned as well as most of it has been replaced. Not the tubes, but they have been cleaned several times.
Whoa.  You've replace carb internal parts?  Were these Honda Genuine or aftermarket?  There have been many reports of "running rich" after switching to aftermarket internal carb parts, particularly the slide needles, which are dominant during cruise conditions.

Floats had to be adjusted to get rid of a stumble we were having in the lower idle range. It is about gone but still a little tricky when cruising down the interstate. They are adjusted 2 mm beyond stock settings.
This is frustrating, as you are asking for precise information without giving any.  2mm WHICH DIRECTION?  Higher or lower?  Was this float adjustment done after the slide needles were replaced?  FYI, higher float levels make all operating ranges of the carbs richer.

What do you do and what are your specific settings to get good gas mileage?
Gotta know what parts and settings the carbs have now before making changes.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

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Offline rangelov

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Re: increase gas mileage
« Reply #13 on: May 10, 2011, 05:33:59 PM »
You need to run the lowest octane fuel for the best fuel economy!!!

Honda CB750s are rated at about 9:1 compression ratio.  Regular grade gasoline is adequate for this condition.

If your engine doesn't ping, knock, rattle or otherwise detonate, use regular fuel without any added "octane" boosters.

Higher octane fuel is SLOWER burning (thus less pre-ignition).  This reduces detonation.  It is bad for fuel economy.  You MUST advance your timing to take advantage of this slower burn, within reason.

If you have detonation or pre-ignition, it should show on your spark plugs.  You will also hear "pinging" from your engine, when severe.

The only time pinging might be an issue is in stop and go traffic in very hot weather.

You might try advancing the timing slightly above stock for better fuel economy.
« Last Edit: May 10, 2011, 05:37:06 PM by rangelov »
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Offline the technological J

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Re: increase gas mileage
« Reply #14 on: May 11, 2011, 08:20:59 PM »
i really dont know any of these suggestions for sure but could a short somewhere be causing low spark voltage or amperage? or bad bearings be causeing extra drag or the brakes dragging?.... are you parachute shaped?
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Offline dl52163

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Re: increase gas mileage
« Reply #15 on: May 11, 2011, 08:25:57 PM »
No just ride a hell of alot and don't give it any rest. I am just dealing with it at the moment and have not had time to think about it. Averaging about 90-120 miles a day on the beautiful girl and I hope that it will continue to provide great service. Even though I am not getting the gas mileage that some of you are it is starting to make me money now.
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Offline SanDogDewey

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Re: increase gas mileage
« Reply #16 on: May 12, 2011, 12:26:43 PM »
FYI, higher float levels make all operating ranges of the carbs richer.

Can you explain how the float level affects how rich the bike runs? I though the float level was set to ensure there was enough gas to feed the jets. Too much in the bowl and they overflow. Too little and the bike starves for gas. What am I missing here?

Offline TwoTired

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Re: increase gas mileage
« Reply #17 on: May 12, 2011, 12:49:52 PM »
FYI, higher float levels make all operating ranges of the carbs richer.

Can you explain how the float level affects how rich the bike runs? I though the float level was set to ensure there was enough gas to feed the jets. Too much in the bowl and they overflow. Too little and the bike starves for gas. What am I missing here?

You are missing:  the distance from the fuel level to the exit into the carb throat.

Works just like a straw in a beverage.  Short straw, easy draw, long straw, harder draw.  The bowl's fuel level, in effect, makes the "straw" distance length shorter or longer.

It takes energy to lift the fuel.  That energy is provided by the differential pressure between carb throat and pressure on the fuel in the float bowl (atmospheric).  Since that pressure differential is the same, the distance of lift variable effects the volume of fuel drawn up from the bowl.  The air volume through the carb throat is unchanged, so if you vary the fuel volume mixed with it, the A/F ratio changes.

This help?

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.