Topic: Increasing Gas Mileage.

[deafanddiabetc]

Got a 74 CB550, the air filter is dirty as hell and I need a new one. But I have brand new tires, don't go over 35mph, idles around 1500 and I never let it rev over 4,000 but I am still only getting about 80 miles a tank. Approx. 20mpg, any suggestions?

[singedebile]

confusing post.

The bike should idle well at 1100rpm (and can idle lower), have you given the bike a full tune up? checked the valves, cam chain tension, timing..?  Your not giving much info...
Is the bike otherwise running "well" you say you keep the rpm's way down... could you go fast if you wanted to? 

...as you mentioned you have a dirty air filter... if its as dirty as you make it sound, that could easily be your problem all around. Get a UNI reusable air filter, they are cheap and you can clean and re-oil them indefinitely.

...if you are still having an issue after doing all the above, then we can keep going (carbs likely need some cleaning), but first start with the basic stuff. Ideally your bike should be getting about 45mpg

[CoachDoc]

You need to thoroughly clean and adjust your carbs for sure, plus a full 3000 mile tuneup. You may also need to replace some of your ignition components (plugs, caps, leads, possibly coils). You've got some major issues- your mileage is less than half of what it should be ( a well tuned 550 will get 45-55 mpg at moderate highway speeds).

[BeSeeingYou]

Sounds like you are only riding around in town.  You aren't going to get much better mileage if it's all stop and go low speed riding in the lower gears.

[phil71]

80 miles to a TANK? I don't care how bad it's running , that's insane. Is that main AND reserve? Does it smoke like crazy, leak gas everywhere? That is practically impossible

[Don R]

Double check your float levels, that's what mine needed.

[Duanob]

I've gotten 80 miles til I had to hit reserve but that was after some pretty spirited riding around town and hitting close to red line just to see how she performs. I've gotten as much as 125 til reserve ~2.5 gallons on a slower highway ride. Check you spark plugs top see if they are sooted up and black from rich condition. If gas is pouring into the cylinders that could cause crappy mileage.

Some causes:
Floats aren't set right.
Float jets have crud in them letting gas flow from the tank into the bowls.
Jet needles have crud build up keeping them from seating into the emulsion tubes.

Im sure other guys can chime in here as well.

[TwoTired]

Got a 74 CB550, the air filter is dirty  Strike one!
as hell and I need a new one. But I have brand new tires, don't go over 35mph, Strike two!
idles around 1500 Strike three!
and I never let it rev over 4,000 Strike Four! (The power/efficiency band begins at about 3500)
but I am still only getting about 80 miles a tank. Approx. 20mpg, any suggestions?

You can get zero MPG if you just stay stopped and run the gas through the motor.
Lower gears make the motor turn faster and use more fuel per distance traveled.
Idling faster uses more fuel than idling at proper speed.

If you never need more than 1/4 engine capacity, never need more than 35 mph, and demand more fuel efficiency, then get a moped.

Has the bike still got the stock sprockets and tire sizes?
Tires properly inflated?
Brakes dragging?
When was the last 3K tune up performed?
Does the bike still have stock induction and exhaust?
Are all the head pipes getting equally hot?

Cheers,

[deafanddiabetc]

I appreciate all the posts, here's a little more info.

I finished building a few months ago and have put on about 1000 miles, but it has new condensers and points that were timed, floats set, carbs synced, new front and rear sprocket including chain, redid all four carbs with kits and new jets (stock size, no rejetting), had one idle jet clog fairly recently and had to open her up again and spray it out.

I guess all in all I completely redid what I thought it needed. The air filter is literally clogged with #$%*, so I'm sure that plays a big role, I'll look into those UNI pods.

[TwoTired]

If you have the stock air box, check out the Uni NU-4055 as a drop in.

Aftermarket "kits" are often the source of running too rich as they aren't always machined to original tolerances.   In particular the main needle taper.

Also, if the emulsion tube bleed holes are clogged, it runs too rich for that, too.

Pods will give you a while new set of issues with tuning.

[jas67]

The air filter is literally clogged with #$%*, so I'm sure that plays a big role, I'll look into those UNI pods.

A clogged air filter is kinda like running with the choke partially on, and will make it run rich, and use more fuel.
Changing to UNI pods will most likely require a re-jet.

[deafanddiabetc]

I hear good things about the "oil and clean it yourself" filters, but is there any issue in just getting a new stock filter to put in there?

[jas67]

I hear good things about the "oil and clean it yourself" filters, but is there any issue in just getting a new stock filter to put in there?

I found stock filters for my CB400F on Bike Bandit.   I was surprised, because new stock filters seem to be NLA for all my classic Honda Twins (see sig for list).

[TwoTired]

I hear good things about the "oil and clean it yourself" filters, but is there any issue in just getting a new stock filter to put in there?

Of course not.

I just found that option more expensive, being they need replacement yearly. The Paper type can't be thoroughly cleaned of all trapped particles.  This makes them drop more pressure across them over time and leads to ever richer mixtures in the carbs.

The service schedule is clean at 3000 mi./6months and replace at 6000mi./12 months for the stock filter.

Long term, the Uni is cheaper, at least for me.

Cheers,

[tlbranth]

When I first resurrected my CB750 my mileage was absolutely pathetic - 27mpg as I recall. I've done a lot of tinkering since then but the biggest gain was from changing the air filter. I got it from Partsnmore and I think it was an Emgo. I've since replaced that one with a K&N. After fixing sticking floats etc., my mileage is 50-55mpg. I think I run the rpms a bit too low - typically 3,000 to 4,500. I try not to bog it i.e. I'm only at 3,000rpm when cruising in a lower gear. But I never run it at high rpm's.

Oops - getting my bikes mixed up. the 50-55 is my wife's VT750. My CB750 gets 42-48 or so mpg

[jamesb]

i increased my mileage by losing about 40 pounds. now the bike is trying to throw me off when we go riding. plus losing a lot of stuff on the bike to make it lighter.

[deafanddiabetc]

@jamesb, I'm 6'4" 200 lbs, if I lost anymore weight I'd be a twig

I purchased a new stock filter from a local, got it for $20. Let me run through a tank and I'll report back on mileage. I have to open the isle screw pretty far to start her (with choke open) and after a few minutes she'll idle at 1000 just fine once the screw is turned back. Is that pretty normal?

I did get 35mpg on a 100 mile trip I took once, I have a feeling with the new filter things will be better.

[phil71]

having to dance with the idle sounds like you'll be digging into the carbs soon. Clogged passages and jets create a lean condition, and that has the motor working harder and hotter to make power. That's one way to lose fuel economy. Another thing worth looking into is if the the float system is not working properly, possibly dumping raw fuel into the cylinders. If your oil is overfilled,  watery and smells like gas, that would be an indication.