Topic: 20 fewer mpg what gives??

[manjisann]

Sorry this post will probably be kinda lengthy so I can give you as much detail as possible.

I've only ridden my bike maybe a month total, spread over 2-3 months.

Juneish I took it to the mechanic and had a tune up done, which included the valve adjust and points and plugs. I rode it for a couple weeks, including one trip of about 150 miles. After that 150 miler I filled her up again and put in approx 3 gallons of gas. I use the mid grade, 88 octane fuel.

I then rode her for a few more days, and decided to redo my steering stem bearings and fork seals. Apparently I did the bearings right, but I over tightened them, which I didn't know, so she steered kind funny. After fighting with it for 2 days, I was tired of it and took it back to the mechanic and had them adjust the steering stem bearings and put on a new chain and sprockets.

I picked her back up on Tuesday, and this last time i filled up, i only had about 88 miles on the odometer and put in 2.8 gallons of gas, which comes out to approx 31 mpg. 

I drive her mainly too and from work which is only about 5 miles away, and around town on short trips. So my question, is city driving, and highway driving mpg really that different?  The air filter is a stock paper one, and is dirty and in need of a replacement. I have new uni filter, but I don't want to replace it and add another variable to the equation till i know what is causing this. I don't ride her hard, im pretty boring really.

Thanks to anyone who can help,

Brandon

[TwoTired]

A dirty air filter will make serious impact on your mileage.

In the city, revolutions per mile are higher because of lower gears use and lots of idling.

How do you now where gas went when the bike was out of your control?

Choke operation uses much more gas.

If you don't EVER ride her hard, the spark plug build up deposit which impede combustion and mileage.

Why don't you tell us the year/model bike you have?

Cheers,

[martino1972]

how well can you trust ur mechanic for not stealing gas..

[OldSchool_IsCool]

Are you dragging a brake?  You mentioned some front end work.  After your next ride, flash touch your front disk to see if it is more then warm.

[manjisann]

My bike is a 73 cb500 k2.

If you don't EVER ride her hard, the spark plug build up deposit which impede combustion and mileage.

I get her up to 6 or 7k rpms easily before I shift, does that count as riding hard?

Choke operation uses much more gas.

Is it really that much more? I only have the choke on for maybe a minute, and that is just in the morning when the ambient temp is chilly. Later in the day I put the choke on, hit the starter, she fires, and I take it off.

How do you now where gas went when the bike was out of your control?

I had thought of that, but I have put approx 35 miles on the bike since I filled her up and it looks like about a gallon of fuel is gone. This is me estimating, heh, so I could be wrong.

In the city, revolutions per mile are higher because of lower gears use and lots of idling.

I figured on ther being more idling, just wasn't sure if it was that much more.

A dirty air filter will make serious impact on your mileage.

I knew this from my car  I just didn't want to change it till I determined if I have another problem, or if I am just a paranoid new parent (this is my first motorcycle ever.)

how well can you trust ur mechanic for not stealing gas..

At what he charges hourly, he had better not be. I had thought of that though. What a sad world it is that we can't trust mechanics... course, then again, that is one reason we do the work on our bikes ourselves right?.

Are you dragging a brake?  You mentioned some front end work.  After your next ride, flash touch your front disk to see if it is more then warm.

I think I am, but would it really make that much of a difference? Guess its time to try and fix that problem.

Ok, so it sounds like maybe I am just over-reacting, and that I need to change the air filter, and fix my dragging brake.

Thanks all,

Brandon

[TwoTired]

I get her up to 6 or 7k rpms easily before I shift, does that count as riding hard?

No. Riding hard mean asking for max power, which is RPM related, but not the sole determining factor.  Say the bike is capable of 50 HP, cruising at 80 MPH @ 6K takes maybe 10 HP.

At least once each ride, after the engine has reached full operating temp, you do a max acceleration run through the gears shifting at red line.  This gets the combustion chambers thoroughly hot, so that the combustion deposits burn off.  This keeps both the plugs and the chambers clean(er), and extends the periods between spark plug cleaning and decarbonizing the head/chambers of the motor.

Is it really that much more? I only have the choke on for maybe a minute, and that is just in the morning when the ambient temp is chilly. Later in the day I put the choke on, hit the starter, she fires, and I take it off.

I think you just told me your air filter is too dirty.  It acts like having the choke partially on when dirty, and therefore you need far less choke when the engine is cold.
I'd guess you have a nice thick layer of soot in your tail pipes, too.

A dirty air filter will make serious impact on your mileage.

I knew this from my car  I just didn't want to change it till I determined if I have another problem, or if I am just a paranoid new parent (this is my first motorcycle ever.)

I don't think I'm going to let you off that easy.    The stock paper filter is replaced yearly, and cleaned at 6 month intervals.  It's in the owner's manual.  If you don't know it's history/age, it can only be established by replacement.  Don't you want to be nice to your bike?

BTW, you only need regular gas.  You are wasting money on higher octanes the engine can't take advantage of using.

The mechanic has to remove the gas tank to adjust valves.  He could have spilled some gas.  My local mechanic say the odds of motorcycle having a full tank are significantly higher if he is required to take the tank off for servicing.  And, the bigger the tank, the more likely it will be full.  Could be that some lighten the carry load.  

Cheers,

[manjisann]

Alrighty, finally got the time and resquared up the front end. One of the forks was a good 3 or 4 mm higher than the other, and now that its all back together, the front wheel spins like a top. So, that problem eliminated, and I also finally put in the Uni air filter, so that will help. I'll keep ya posted.

TT, I mainly ride her in the city and rarely get above 45. If I wait till 8 to 8.5k rpms before shifting, will that help to keep my plugs and cylinders clean of carbon build up?  Or do I need to really go all out and take her up to 60 or 70mph? (i know, that isn't really all out, but I'm kinda chicken about the higher speeds, and Utah drivers are aweful on the roads )

Thanks,

Brandon

[TwoTired]

You need to make the engine work at higher RPMs occasionally.  You can use lower gears to do this.  Just wait till the engine temps get normalized.  Then "show off" with max acceleration at least once a ride.

If this is beyond your desires, then change spark plugs more frequently, if they soot up.  Or, invest in a spark plug blast cleaner for your compressor, to freshen sooty plugs.  Something like this:
http://www.amazon.com/gp/product/B0002STSD0

But, maybe the new air filter will help the sooty plug situation.   

Cheers,

[manjisann]

Well, right off I can tell you it feels different without the brake drag  . I'm already at 80 some odd miles, and still have at least half a tank left, so that made a difference. Needless to say, don't think I will go back to the mechanic anymore. With the help of this forum, I should be able to do whatever I need. Just might have to take a break now and then, so I don't break the bike in frustration 

Thanks,

Brandon

[manjisann]

Ok, so I filled the bike up again today and only got 34mpg from the last tank. I realize there is a difference in mpg between highway and city driving, but is it realy that big of a difference? What kind of mileage do most people get out of their CB500's? Could I be running too rich? I have my idle set around 2000, which I know is higher than manufacturer spec, but if I lower it much past 1400rpm, it dies. I also have found that if I ride it at above 6000 rpms for more than half a minute or so it starts to backfire.

I guess the question here is, am I expecting too much out of an old bike?  I figured I'd get at least 40mpg out of it.

Any thoughts?

Brandon

[martino1972]

backfiring above 6000 rpm for a while sounds to me like fuel starvation..fuel cant get fasdt enough to the carbs..

[manjisann]

Fuel starvation, I was wondering if that is what it was. Seems I may have set my floats too low. Would this potentially cause me to lose mileage somehow?

Brandon

[martino1972]

Fuel starvation, I was wondering if that is what it was. Seems I may have set my floats too low. Would this potentially cause me to lose mileage somehow?

Brandon

well,there's a million factors giving you good milages or not,but it's sure a sign somethings not good in the fuel delivery...
as problems are getting solved,you should see increase in mpg....
but much better then 40/42 mpg you probably won't get....

[martino1972]

tire pressure oke???
maybe take some time and run her on a highway for awhile,see what mpg you get there(good excuse for a trip.. )
34 mpg in city doesnt seem to be too bad for city driving,i would say...

[TwoTired]

Ok, so I filled the bike up again today and only got 34mpg from the last tank. I realize there is a difference in mpg between highway and city driving, but is it realy that big of a difference? What kind of mileage do most people get out of their CB500's? Could I be running too rich? I have my idle set around 2000, which I know is higher than manufacturer spec, but if I lower it much past 1400rpm, it dies. I also have found that if I ride it at above 6000 rpms for more than half a minute or so it starts to backfire.

I guess the question here is, am I expecting too much out of an old bike?  I figured I'd get at least 40mpg out of it.

Yes, it should get better than 34.

The first clue, is that you can't get it to idle at 1100 minimum.  That fact demonstrates a problem, probably in the carbs.  My first guess would be an issue with the slow system, which is supposed to supply most of the fuel used by the engine at idle settings.  This circuit is also called the pilot circuit as it supplies some fuel at ALL throttle settings.  So, if it is not doing it's job then upper throttle setting run leaner, too, to some extent.

It would probably help with diagnosis if we knew about your exhaust and air filter.   Did you ever vacuum synch the carbs?  What is the tune up history?  And, how do you know the last one was done right? Re-reading your initial post, I'm surprised the mech that did your tuneup didn't flag the high idle problem before returning it to you.  His prowess is now suspect.  And, that casts doubt on the rest of the tuneup quality.

The idle/slow/pilot circuits are the stingiest with fuel.  And, you aren't using them.   Of course you'll use more fuel than you should. 

My 550's get around 50 MPG with highway cruising in upper gears.  City driving, 40-45-ish, depends on the ratio of stopped vs. moving.  And, I can't keep myself from giving the throttle a good twist every now and then.  Except for the Uni filter, windshields, luggage rack and/or fairings, my bikes are stock.

Cheers,

[manjisann]

His prowess is now suspect.  And, that casts doubt on the rest of the tuneup quality.

Sadly, I lost faith in them when they didn't square up my forks like I requested. Looks like I need to buy a set of vacuum guages and do my own vacuum sync. Does anyone know if these ones from Z1 are decent? http://www.z1enterprises.com/detail.aspx?ID=2727   I realize they are probably not top of the line, but will they do a decent job?

To the best of my knowledge the only things on my bike that are not stock is the shorter handlebars I have, the Uni Air Filter I just installed, the sissy bar, and the Mac 4-2 exhaust. As far as I know, the carbs should be stock. I think I have the levels in my carbs set a bit low, as I backfire after a bit when running at 6krpms or higher.

When the bike is up to temp, it does idle better at lower rpms, but as I said, still not well at below 1400, which you are indicating is a problem.

So, if I understand both TT and martino1972 correctly, I need to check my float levels (this may fix the backfiring problem) and I need to vacuum sync my carbs to see if that is off. Is this correct?

Thanks to all,

Brandon

[TwoTired]

I'd check the head pipes for even heating.  If you have cold(er) ones with the idle set as low as it will go, I'd clean the pilot jets in the corresponding carbs with the colder cylinders.

Yes to carb sync.  And, yes, check float levels.  But, levels have to be pretty far off to effect idle as you describe.

The gauges in your Z1 reference look like mine, only 30 years cleaner, and my plate mount is red.

Cheers,

[manjisann]

Unfortunately, I have spent my chunk of money this season, so I don't have the money right now for the guages. If I ride the bike like this for the next couple months, am I going to potentialy damage anything. It seems like I read that running lean can damage the pistons or something due to overheating. Can I finish this season with it the way it is, properly winterize and then un-winterize (is that a word??) and tune it up at the beginning of next riding season when I have some more money to buy the guages and such? If all I am losing is mileage, and I have a good idea of what is causing it, I am fine with that as long as it does not damage the bike. There is only 21000 miles on it, so I would really hate to do anything that would force me to rebuild it prematurely.

Thanks again,

Brandon

[TwoTired]

Take out your spark plugs and take a picture of the tips.  If you are running lean, they will show it.

You can check relative head pipe temps fairly easy.

Cheers,

[manjisann]

As requested, here are the pics of my spark plugs.

This is cylinder 1.

[manjisann]

Sorry, I am not sure how to embed multiple images in and be able to lable them without multiple posts.

Cylinder 2

[manjisann]

Cylinder 3.

This one looked a little wet, not sure if it was from oil (cringing at that thought). It also had some grit on it, which may have come from when I pulled it out. Didn't think to blow out the head area before I removed these, till just this second.

[manjisann]

Cylinder 4

[manjisann]

*sigh* I also think one of my gaskets is leaking, as I have a small amount of oil on some of the lower fins. I read one post where someone had a similar problem and it was suggested that they tighten the bolts to ensure that the head and such was tight. Where do I find the torque specs for the bolts and nuts on the bike. The clymer has a few specs, but not many, and I have a very nasty habit of overtightening things, and I really don't want to do that. If tightening the heads down doesn't do it, I have ordered a gasket set that is supposed to have all the gaskets to redo an engine from top to bottom. Plus, if what I am afraid is wrong with cylinder 3 and the rings are going out on it, I have to at least do those as well. If that is the case, how hard is that kind of rebuild and is it pricey if I do it myself? Do I need to replace the rings on all the pistons, or just the one. And can I get away with doing it with the engine in the frame? What else would I need to know, and am I jumping the gun?  If I have to do a rebuild, that would be sometime  next spring, as I don't have the time or money right now.

Thanks all

[TwoTired]

None of your spark plug look to be running lean.  Plan on replacing spark plugs often.
Sniff the wet one.  Gas and oil smell different.  Compare with your dipstick and the open gas cap.

My metric is if the oil is dripping on your pants soon after cleaning, then it's time to pop the top and replace the oil passage orings.  Otherwise, I simply clean the oil every month/week.
It is unlikely that re-torquing the head will restore oring seal to 30 year old hard baked orings, IMO.  You'll have to take off the cam cover to do it.  And, if you aren't careful putting it back on, you'll bend valves. (about $50 each)  You'll have to buy a torque wrench, and most likely an impact driver to loosen the cross point screws.

Good lord, you're planning on a ring job and you haven't even done a compression check yet?  Do you have issues with depression or excessive worry?   

Cheers,