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Discussion Starter #1
I bought a '99 Honda CBR600 F4 back in 8th of this month. And there's a little maintenance issues that needs to be done. For example, replacing the front tire and changing the oil. Also when the speed drops below 20 mph, the front brake fades in and out, it grabs and then it lets go every 1/2 second.


Anyway, my question is I'm not sure why, but the bike is really burning a lot of gas. Most of my riding is in town with few traffic stops, so far haven't done any freeway riding with the CBR. Mostly I stay in 3rd or 4th gear, and sometimes 5th for few minutes on long stretch of road. Mostly I let the bike cruise at 5-6K rpm and occasionally let it fall at 4K rpm during braking. When accelerating, I don't usually take it above 8K rpm, mostly run it at 7K rpm before shifting up.

So with all that said, I'm getting 80-90 miles out of 3.7 gallons of gas before it hits the reserve, that's about 21-24 mpg.

The bike itself seems to run fine, carburetes well, no hesitation on starting it up. Once I notice white smoke coming out of it when it was cold and gave it some throttle. But that's about it, I never need to use the chole to start it up. There's no hesitation in any of the gears or rpm, and it pulls quite smoothly.

The rear tire is practically new, and like I said, the front tire needs to be replaced, it's pretty bald.

The bike seems stock, no aftermarket stuff, even the OEM license fenders is still there.

So I'm just scratching my head about what could it be? I get even better gas mileage on the SV and my car.

Here are few pics:

http://files.automotiveforums.com/gallery/showphoto.php?photo=46986&password=&sort=1&size=medium&cat=500&page=1
http://files.automotiveforums.com/gallery/showphoto.php?photo=46987&password=&sort=1&cat=500&page=1
http://files.automotiveforums.com/gallery/showphoto.php?photo=46988&password=&sort=1&cat=500&page=1
http://files.automotiveforums.com/gallery/showphoto.php?photo=46989&password=&sort=1&cat=500&page=1
 

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Discussion Starter #3
200 on full tank, what gear? it seems odd for my bike, but no freeway riding either. like I said, I usually stay in 3rd and 4th pending on traffic.
 

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You mentioned you feel your front wheel grabbing. Take your bike out and go about 55, and then squeeze your brake. Do you feel a pretty strong vibration?

I'm guessing one or both of your front discs are warped, and your brake calipers are dirty. This will drag your mileage way down. The rear brake caliper is even more prone to dirt-induced dragging than the front. Take a two-mile ride without using your rear brake and then touch the rear rotor. Is it hot?I also expect you could use new plugs, and your air filter could stand a good cleaning. How's the chain. Dry, worn, or too tight will also make your bike drink gas.

These are all relatively minor things which you can easily fix yourself. If you're not used to working with brakes, you should either get a manual, and let the fellas & ladies out here help you through it, or let the shop do it.

If you go the shop route, make sure they know you want the calipers thoroughly cleaned. Be a good idea to change the pads also if your wallet will stand it.....Hope this helps...

PSI looked at your pics and the bike looks stock, clean, and well cared for, so just check out those things above and you should be in good shape...
 

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Discussion Starter #5 (Edited)
Thank you. Ya, it's exactly as you described it, on high speed, the brake does work pretty well, but I get this really strong ringing vibration through the bars, and no matter how hard or soft I brake, it 'feels' like the forks are compressing tight. It vibrates strongly every time. Also I'm not sure if it's normal, but there are some minor vibration through the bars when cruising.

I'll see if the rear disc is warm tomorrow, but when I had to repair the rear tire, the dealer mechanic said the rear needs brake pads. I know it does because I experienced fade. And when I got back from the dealer, it seemed the wheel was mounted tighter than I had before. Chains seem fine, but probably needs lubing, but it seems there's not much slack.

I can probably take care of the brake pads, but what happens when brake discs are warped? Anyway to fix it?

I let a very good friend of mine ride it, he didn't mention anything about vibration, but he said the brake fade could be due to brake discs being warped and needs a new tire.

Also I heard that the older CBR6s are known for having bad cam-chain tensioners, how would I know if it's disfunctional? Is there long term solution to this?

I'll take some closer shots tomorrow if it helps.
 

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Hi Z_Fanatic-

You might also want to double-check your tire pressure to ensure they're not way too low. That could certainly lead to gas-guzzling. I like to start looking for a gas station when my main tank hits about 130 miles or so. I'll have to run it down to empty to see what kind of actual mileage I'm getting on my CBR 600F2 for comparison purposes.

In terms of the cam chain tensioner (CCT) going bad, you'll know because it will sound like a bunch of loose marbles being rattled around in a coffee can. The sound is mostly noticeable from the right side of the engine at idle and then will go away once throttle is applied. It is annoying in nature, but won't be a "code red" situation that needs to be addressed immediately. The best bet is to remove, clean, and reinstall your current CCT while you shop around to get the best deal on a stock CCT or one of the aftermarket manual CCTs that are advertised. Due a search and you'll see lots of threads on this topic (including pictures) and how to do it.

~ Blue Jays ~
 

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Sounds like warped disks are the problem. They would be dragging, so its like riding around with a brake applied a tad. Bad on gas milage. Now the trick is finding out which one is it.
Car disks can be shaved a tad to get a true surface, so long as they are not too warped. I dont know if the same can be done to bike rotors or not. My guess is no since they are so thin.
I'd advise finding which rotor is warped and scoring a replacement on ebay.
 

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Warped rotor. Guys, be careful how you handle wheels when they're off the bike. It's not hard to warp one of these floating rotors from banging them around while off the bike. It's generally the hub that bends when hit, not necessarily the rotor itself but once done, it's the unit that needs replaced.

You probably won't even need any fancy measuring tools to find the culprit. With the wheel off the ground and a screwdriver held stationary against the lower leg, spin the wheel and see which one is friendly, waving at you.;)

The fuel mileage may be the result of an overzealous jetting job. Especially when you say that no choke is needed on cold start. If you get a Xmas card from the Saudi royal family, you can be sure of it.
 

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Good tips up above. Still check on the teeth of the small & large sprocket for you might find the prior owner went down one tooth on the front so YES you will use up more fuel, but probably only on the hwys.

You have to realize the sportbikes were never designed for puttering around in the city traffic for that is where a regular riding position bike of nothing larger then 500cc will prove to be the good bike when it comes to fuel use.

When it seemed like fuel prices were high in the late 40s or to the 60s I noted chaps with larger bikes like 500cc to 750cc to even Harley 74OHV would latch onto a smaller bike, for around town, like a 125 2-stroke, to 250cc 4 stroke to even 350cc single 4-stroke & yes AS a 2nd bike.

I used my bikes to & from work so rode anything from 125cc to a 350cc & yes that included the little old Villiers 125cc 2-strokes to the flat opposed liquid cooled 175cc LE Velocette. There simply was no need of a 500 to 1000cc bike when in town town riding. Though these were not LARGE cities like in the States so traffic tie-ups were almost unheard of.
 

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Discussion Starter #11 (Edited)
Haven't taken off the fuel tank yet, so I'm not sure if it was jetted. After I take it off, would I be able know it with naked eye looking at the carbs or throttle bodies? The rpms are already set as the book is directed and it's smooth, the needle is not peculiarly bouncing off as a poor jetting would indicate, like my previous bike. And every single time I hit the starter button, the bike comes to life with one push.

As Rundog advised, I took a 10 mile trip around town, no stops except for traffic light. When I brought it home, the front two discs were burning hot, couldn't touch it for long. I didn't use any rear brake, so the rear disc was wee bit warm, but no more than the saddle and heat dissipating from exhaust and hot sun. When the rotor cooled down, the rear disc went cold fast while the front discs were still a bit warm.

CCT seems to run fine, for now.

No other niggles, if I didn't apply the front brake or checked out the trip meter, there's no way to tell if anything is wrong with this bike. There's a little scratch and scuff marks on the left fairings and clutch cover from the previous owner tipping the bike over on low speed in sand and gravels.

Here are a few more pics, with closer look on the discs:












PS. after I strip the fairings, how would I know if the sprockets are aftermarkets from stocks?
 

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Try riding around the block a few times without using your front brake at all. You dont have to go over 20mph, so a rear brake should stop you just fine. See if the rotors still get hot, in particular if one gets hotter than the other.


As for sprockets, the only thing I know of, is to find out the stock size sprocket and count the teeth
 

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Bikes are usually rejetted to accomodate an aftermarket exhaust. Your exhaust appears stock. I would say that your sprockets are also stock, since your bike is wearing its original chain guard and they appear to be made of steel. I'd take care of the brake problem first. As V. said, the rotors are to thin to be machined & must be replaced. They are not cheap. Look into aftermarket rotors such as Galfer, Braking, or EBC. You could go to a salvage yard or Ebay, but you risk getting a set that are as bad as what you already have.

Check to make sure that your airbox & filters are clean. Being able to start your bike without using the choke is usually a sign of a very dirty air filter, or an obstructed airbox.

Like BJ said, low tire pressure will not only affect your mpg, but also your handling...........
 

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Discussion Starter #14
Really, that sounds very strange. A bike being able to start by itself in warm weather w/o choke could mean dirty air filter. I had problems on another bike with starting it up because it has dirty filter among other things :D. But I am going to replace air filter/oil filter anyway, I did it every time I bought a bike.

I just got back from riding, first around the block for 10 mins, proceeding 20-30 mph using only the rear brake. Then pulled over and noticed the rear was hot this time, and the front stayed more or less cool. And then I let the rotors cool for a while, and headed onto mainroad for high speed. This time using only the front. The rear rotor remained cool, and both front rotors felt hot equally.

Checked tire pressure, and it's optimum to specs 36F/42R.

Looked at ebay, and you're right, the used ones are another gamble. So is there any aftermarket parts site? I checked bikebandit.com, and new OEM rotors run about $274.00 each, ouch!

Btw, if I jack up the front wheel and spin it, I should be able to tell if rotors are bent? I mean they'd be spinning and waving right? I probably need a help of a friend with this, since I dont have a front stand, only rear wheel stand.
 

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Z_Fanatic said:
Really, that sounds very strange. A bike being able to start by itself in warm weather w/o choke could mean dirty air filter.


Btw, if I jack up the front wheel and spin it, I should be able to tell if rotors are bent? I mean they'd be spinning and waving right? I probably need a help of a friend with this, since I dont have a front stand, only rear wheel stand.
When the motor is cold, it needs a richer mixture. Dirty air filter = richer mixture....

Check out Dad's post for how to examine the rotors. You'll definitely need a friend's help if you don't have a front stand. You can remove the fairing lowers and use a floor jack with a book or piece of wood between the jack and your exaust headers to lift the front, but the bike will be very unstable while in this position.
 

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You need some measuring equipment to properly analyze your rotors... I know what the thingie looks like, but not sure what its called
 

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Does the bike coast easily? Check wheel spin and chain adjustment. The waver feeling may be due to the tight spot in your chain. (Actually caused by sprocket out-of-round)

Look at your exhaust ports, oily, carbon, or grey? Should be mid to dark grey.

Look at your spark plugs. Adjust or replace if necessary.

Maybe your odometer is off.

I get 40-55 MPG on all my bikes no matter how I ride. (Except for track days.)
 

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Discussion Starter #18
Wheel spin and chain is on the tight side once I got back from the dealer. I'm not sure how chain sprockets could affect the front brake wavering and pulsation on the bars. Odometer... that's a good call, I'll measure it today if it's more or less accurate. Exhaust is full of carbon, black, dark grey... but never oily. What I did notice is some carbon deposits on the front rotors.
 

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Is there a smell of gas while sitting on the bike while its running? I was just pondering fuel loss OTHER than burning it up.

I presume this is a gravity-feed fuel system.
 

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Vash said:
You need some measuring equipment to properly analyze your rotors... I know what the thingie looks like, but not sure what its called
That's a dial indicator reading out in thousandths of an inch BUT... if it's bad enough to feel at low speed, it's often bad enough to pick up with the naked eye when compared to a closely positioned fixed point.
 
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