Hey all!, I have been around bikes all my life and got to work on a few in my younger days but nothing like what I have my hands on now. I bought my first sport bike a few months ago as a fixer' upper' project as it is a salvaged 1997 CBR 900rr. For the most part (or from what I can tell) the bike is sound with the exception of fuel consumption. I am not riding aggressive and I am only pulling in 50-80 miles per tank. I know this isn't right by all the other threads and search's I've done across Google and sport bike forums of 30-40 MPG. When I bought the bike the previous owner did say that her husband (R.I.P) had plans at one time to turn it into a stunt bike but didn't know what all if anything was done to it in that regard. So if he messed with the carbs (Rich/lean settings or re-jetted it), I wouldn't think it would/could be that drastic of a difference.

I am trying to keep this DIY as much as possible as I like to have ownership in what I own and ride so, Any help or insight on where to look would be great!!



Parts replaced so far....
Chain and sprocket set to factory 16t drive and 43t final drive (had 15t and 45t final)
Clutch
Clutch cable
Left handle bar
Rear brake pedal
Alternator cover

Parts pending replacement....
Forks seals
Cowls, side covers and windscreen (plastic welding/mending and repaint)
Fuel petcock (cover set and hoses)

 

How far are you riding it, when you ride it?

Have you been doing a lot of idling in the driveway working on it?



And are you sure you're not leaking anywhere from the petcock (since you said you were going to replace it) or fuel hoses?

 

Pull the plugs and see if it's running super rich.

Has there been any mods to the tank?
It's either leaking/evaporating or burning. Maybe both.

 

Conrice - almost daily driver (minus high winds and rain) now that weather is nice enough for about 20mi round trip. Idle time is just warm up before riding, less then 5 min.

Demon - Will pull the plugs again but nothing stood out before when I had them out. No deliberate mods to the tank (other then a couple small impact dents).


There is no obvious signs external leaking around the petcock or hoses unless it evappin' that fast. <The drain tube under the tank has been blocked off. So I have to siphon the tank to empty it. The breather line are gone for now but will soon replace those. My understanding is the breather line (from microfiche) looks to act as a bypass for air and fluids from the top (under the fuel cap) of the tank to the bottom to keep crap off the tank (gas, etc.). Also the line that comes out of the cover set (petcock diaphragm) is blocked off as the cover set needs to be replaced as well. >

 

i have question while trying to think this through, is there a smell of gas when the bike is running???
also its a 97. so it doesnt haave a fuel pump and the gas is sucked in to the carbs by vacuum. there should only be one vacuum to the block.. i would just check to make sure you dont have too much vacuum.

 

Now that you bring that up the past few rides to and from work I have notice a gas'y' smell. I have a terrible sense of smell to begin with and the cooler temperatures and air/barometric pressure when I first started riding the bike may have kept the gas'y' smell from ever reaching my nose. Also may have assumed the smell was coming from other vehicles around me when stopped or slow moving. Will have to look at that as well.

Is there a way to adjust the vacuum if too much pressure?, through carb settings/adjustments?

 

Check the air filter to see if it needs changing. In fact with any new (second hand that is ...) bike give it a full service. There's a suspicion that the PO messed with the carbs so take them off and check that the jetting is stock (you don't mention the exhaust so that may have an impact there). You say you 'wouldn't think it would/could be that drastic of a difference'. I say ' never underestimate the stupidity of a PO' .... :-)

Dave

 

What do your plugs look like?

 

I don't have a garage so have to wait for nice enough weather to take the bike apart to get to the plugs and take off the carbs. The air filter is good as it's a K&N and I cleaned it just after I bought it.

 

lol oops i forgot that my post got ot get approved by a mod before it posts to the public.... my bad......