Topic: Better gas mileage on the 550

[Tews19]

I know there have been threads about this.

I want to highlight the article written by Mystic,

Increasing Gas Mileage – CB550
By admin, on April 24th, 2009
Submitted by Mystic (and others)

Not trying to sell anything, just thought I would regurgitate an old trick that went around the dealership I worked at in the 70′s. Since we’re about to have another gas crisis it just seems appropriate again. This is all from memory and was confirmed by myself. Don’t know if it works with other bikes but it should.

I don’t have parts in front of me now but it went something like this… Remove main jet,… Look into throttle bore and see a small brass thing sticking up,.. push down on it with a screw driver and it should fall out. Crawl around on knees till you find it and you will be holding the emulsifier tube. It has a series of holes drilled on opposite sides. Drill more of the same size holes between the existing ones, essentially doubling the holes. Do one at a time and put it back in the same way it came out. Compare to other carb to get the orientation.

This tube mixes air with the fuel coming up around the needle and makes it sorta foamy (or emulsified) Apparently it atomizes better when it enters the airstream as a foam? The main jet and needle/needlejet do the fuel metering. somewhere there’s an air jet feeding the emulsifier area. None of these things have changed and no re-jetting is required,.. It just emulsifies better.

END OF ARTICLE

I am curious who has done this? I have to swap out my main jets hopefully tonight or tomorrow from 100's to 105's. I am doing this due to hesitation at high rpms. I have the stock 069 carbs for my 75 550F.  They originally came with 95 mains, 38 slow. Everythign minus the mains is stock. I run the stock 4-1 header with my Lossa muffler.

If I pull the emulsifier and drill extra holes; from my understanding my MPG will increase.

Will this effect the response, cause any hesitation when riding? Make my plugs run to rich? The article states no rejetting will be needed.

What size drill bit would need to be used?

If someone has done this; has access to the emulsifier tubes, please post pics and results?

Thanks everyone

[xsmooth69x]

watching this!

twotired dave500!!

[Tews19]

I was going to PM them but I always do. They probably hate me by now

[kayaker43]

I'm the originator of the above information. I have done it on three 550's all with improvements and no changes in jetting or the way the bike ran but I spent a lot of time getting the jetting right before the mod. If you are having hesitation or flat spots due to borderline jetting dont expect this to fix it.

I went on a 750 mile highway trip right after the mod and got a consistent 60 mpg on my 75 550 which matched a CB360 I was riding with. Gas was 60 cents a gallon at the time so this was a long time ago. I've repeated it over the years and to this day haven't gotten anyone to try it and confirm or deny the results.

You mileage may vary,.. sorry couldn't resist

[Tews19]

I'm the originator of the above information. I have done it on three 550's all with improvements and no changes in jetting or the way the bike ran but I spent a lot of time getting the jetting right before the mod. If you are having hesitation or flat spots due to borderline jetting dont expect this to fix it.

I went on a 750 mile highway trip right after the mod and got a consistent 60 mpg on my 75 550 which matched a CB360 I was riding with. Gas was 60 cents a gallon at the time so this was a long time ago. I've repeated it over the years and to this day haven't gotten anyone to try it and confirm or deny the results.

You mileage may vary,.. sorry couldn't resist

Thanks! I wasn't planning on this to fix the flat spot/hesitation. I know I need to go up one jets size. I was curious if once I got the jetting correct, would this cause the same hesitation once I corrected the proper jetting. Can you tell me the drill size and possibly show a pic of the emulsifier tube with new holes

[TwoTired]

The theory is sound and the extra holes will lean the mid-range to wide open throttle.  However, ethanol gas does this too, and wasn't in widespread use in the 70s.

I have not tried it as my bikes run well and get 45-55 MPG as is, and that's good enough for me.

I will warn about making multiple changes at a time.  As you won't know what change did what and it will become more confusing if you don't get the home run to have it all work out perfectly.

I'd get it running well first.   The Lossa muffler is not stock and of unknown pressure characteristics.  And, the stock #98 main was selected for a higher pressure muffler.

I've already told you to start the carb fine tune odyssey with the settings for 022a carbs.  #100 main, and needle in the 4th from the top.

My 75-cb550K (022a carbs) got 45-50 mpg commuting city/highway on non-ethanol gas. and Vetter V windjammer fairing on it.  It did this with a 4 into 2 exhaust system and with the stock 4 into 4 pipes later on.

Do what you want.  Tinkering with the bike can be as much fun as actually riding it.

Cheers,

[Tews19]

The theory is sound and the extra holes will lean the mid-range to wide open throttle.  However, ethanol gas does this too, and wasn't in widespread use in the 70s.

I have not tried it as my bikes run well and get 45-55 MPG as is, and that's good enough for me.

I will warn about making multiple changes at a time.  As you won't know what change did what and it will become more confusing if you don't get the home run to have it all work out perfectly.

I'd get it running well first.   The Lossa muffler is not stock and of unknown pressure characteristics.  And, the stock #98 main was selected for a higher pressure muffler.

I've already told you to start the carb fine tune odyssey with the settings for 022a carbs.  #100 main, and needle in the 4th from the top.

My 75-cb550K (022a carbs) got 45-50 mpg commuting city/highway on non-ethanol gas. and Vetter V windjammer fairing on it.  It did this with a 4 into 2 exhaust system and with the stock 4 into 4 pipes later on.

Do what you want.  Tinkering with the bike can be as much fun as actually riding it.

Cheers,

Thanks TT. I have followed your advice to a T. No pun intended. I will swap the mains. Ride for a while and get back to you. My mileage now is around 40 MPG. That is when I flick the reserve on. I ran out of gas once and it wasn't fun. I won't let it get to that point again to get an exact MPG.

BTW, I really like tinkering. I bought a carb synchronizer two days ago to allow me to do it anytime I want, no more borrowing. When a bike runs well and I know it's cause of my effort. Nothing beats that feeling.

[ekpent]

Little off track,don't know how many still gets Cycle World magazine but long time Wisconsin Good Guy Peter Egan got a 550 recently and has put it on the road. In the last issue he was commenting he was getting less than 100 miles before reserve hit,think he said around mid 30's or so. Some of my 750's will get 50+ when I am on a tour. 550's were never known for super great mileage as noted also in his article, good read.

[Tews19]

Little off track,don't know how many still gets Cycle World magazine but long time Wisconsin Good Guy Peter Egan got a 550 recently and has put it on the road. In the last issue he was commenting he was getting less than 100 miles before reserve hit,think he said around mid 30's or so. Some of my 750's will get 50+ when I am on a tour. 550's were never known for super great mileage as noted also in his article, good read.

My 78 550 was like that. Right when I neared 95 miles I put it on reserve... I have lots of old vintage magazines my buddies dad has been giving me.

[bboyroxas]

My bike runs fine I get 40 mpg because I have no mufflers and I have rebuilt carburetors with the normal jets should I do this mod will it increase that much I can go like 90 before I have to switch to reserve my tank is just a little over 3 gallons.

[kayaker43]

I didn't mean to imply I invented anything, just that I posted the information being quoted now. The emulsifier trick was pased on to me by another mechanic who said he saw it in a Honda bulletin. sometime later I did see that bulletin but don't have it now. Not sure if it was 550 specific or a general thing? Perhaps someone can dredge up a copy?? I seem to remember it saying drill the same size as existing holes whatever that is and it wouldn't affect mixture which matches my experience with it. Regardless of what it said, that's what I did and it worked well. I don't have a set of carbs apart but still have one bike is storage with the modification.

Hey its free, its easy, and there appears to be no downside. Over the years all I get is debate over why it will or won't work. I'm just the messenger and can accept that some things work whether we can explain them or not. I'm really hoping others will just try it and report back. It may take longer to debate it than to try it if you are already changing main jets.

Ethanol actually decreases fuel mileage besides causing other corrosion problems. That will spark a debate but consider that when running pure ethanol, the jet sizes are roughly doubled in area because of the lower energy density compared to gas.

[lone*X]

Drilling holes in small round tubes can be very tricky and would not be something to try with a hand drill.  Make a gig to cradle the emulsifier tube and keep it aligned under a precision drill press.  Go slow and use very little pressure.  Lastly I would never modify the only parts that I had for a good running bike.  Screw it up and you are sidelined.  Get a spare set of emulsifiers to drill, then if they don't work out you are not dead in the water waiting for more parts.

[Tews19]

I will definately try this at a later date and report back. I think its cool to learn how to cheap mods and see it be successful.

[kayaker43]

I drilled one set with a hand drill, yeah it was tricky. The other two sets were done with a drill press because I had one. Either way you need a tiny dimple to get the drill started. its pretty low risk and would cause no problems if done sloppy. The hole size and spacing doesn't seem critical, its just aerating the fuel more. My holes were not perfectly spaced at all.

The hole size is the same as existing holes so we effectively double the area with no apparent changes to mixture. Obviously smaller holes will have less than no effect, its just not fussy. I've already spent more time typing than it takes to try it.

I would do it by the side of the road with a cordless drill if I had a couple spare drill bits. the emulsifier tube has a thin wall so even a broken bit can be poked out easily.

No more excuses,.. no more theorizing, somebody just try it and tell me if I'm crazy! It was in a honda bulletin for gods sake but you can blame it on me if it doesn't work.

If it works please send money 

[singedebile]

two quick questions,
-do you know what size the holes are (that I may order the mini drill bit required)
-are the holes drilled in line with the existing ones vertically or are they drilled perpendicular to them?

Looking forward to trying this the next time my carbs come off,

[Deltarider]

So far I've not seen any proof.

[Duanob]

I usually average 40ish MPG on a 1976 550. Memorial Day weekend I went for a long country ride with no stop and go traffic, averaging about 50MPH and got a surprising 50+! It was surprising to me anyway.

[dave500]

i get 200 klm before reserve,sometimes 220,i wont be drilling my tubes in a fuel saving effort.

[xsmooth69x]

i get 200 klm before reserve,sometimes 220,i wont be drilling my tubes in a fuel saving effort.

200km = 125miles

metric system pshhh... wish the states would just convert that would be nice....

[Deltarider]

who said he saw it in a Honda bulletin.

Interesting... but where is it?

I usually average 40ish MPG on a 1976 550. Memorial Day weekend I went for a long country ride with no stop and go traffic, averaging about 50MPH and got a surprising 50+! It was surprising to me anyway

Well, what can we say..., it was a memorial day.

i get 200 klm before reserve,sometimes 220

What tank? How many liters? 500? 550?
So far only small talk in this thread and no science.
This forum once more as echo-pit.

[kayaker43]

OK I dug up the old thread from 2008, you will find more info there along with some validation and the usual skepticism.

http://forums.sohc4.net/index.php?topic=32544.0

[hoodellyhoo]

I'm too lazy to read every post in this thread but here's an article I scanned about improving the mileage on a 550 from a 1982 Cycle World magazine. Click on the text that says "The mileage mystery...."

http://www.sohc4.net/index.php/cycle-world-1982-improving-the-cb550-gas-mileage/

[Stev-o]

wont be drilling my tubes in a fuel saving effort.

+1.  I have never calculated gas mileage on any of my bikes.

My Tacoma once got 20 MPG, I was quite pleased (highway trip in winter w/no ac)

[TwoTired]

I seem to remember it saying drill the same size as existing holes whatever that is and it wouldn't affect mixture which matches my experience with it.

Wait.  That makes no sense.  If it doesn't change the mixture ratio, how can it improve economy by using less gas per mile?

Ethanol actually decreases fuel mileage besides causing other corrosion problems.

Agreed.  Though it is relevant that ethanol also leans the mixture, forcing you to use more of it to extract the same energy.

Adding air leans mixture.
Adding ethanol leans mixture.
Adding both, leans mixture cumulatively.

Certainly if you at a higher altitude the engine can stand both.  I'm not so sure about sea level with low humidity, high barometric pressure, and cold air.
The carbs were originally adjusted for median conditions world wide.  How often do you encounter real median conditions?

Curious that if Honda knew about this, they didn't apply it to later models getting scrutiny from the EPA.  Or, make it into a rolling change for production models.  Not that this is any sort of proof.  But, I'm thinking there is something we aren't accounting for.

Cheers,

[singedebile]

TwoTired, I think the idea was that it atomized the fuel better (from what I understand reading this thread), so likely burning more of the fuel that is already there, meaning you would need to use less fuel for the same amount of power.