97 CBR900RR fuel consumption issue
 

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......

No big deal.

Not anymore.... :D

Oh, and at least start the bike up and let it run for a minute before pulling the plugs (i.e. don't go out 3 days from now and pull the plugs without running it first - otherwise it won't tell you much).

weather hasn't been too nice tonight but was able to siphon the tank and leave enough in to let her run for a few minutes or so before taking the tank off to get to the plugs.

hey williepete,
i've been working on my own project the last couple days anyway jjust so you know if you want to post any pictures to us, just go over to photobucket upload whatever you like and when you reply (in here)and want to post a picture just go back into photobucket and copy the pictures url image (it will be on the right hand side of photobuckets screen)and paste it after your done with the text..
the reason i mention that is you have the tank off and if you want to snap a couple shots of the vacuum lines and carb setup we mught be able to spot something out of the ordinary.
now back to gas smell, if you keep the tank off and setup a temporary I.V. bag with gas in it and then run the bike, i would run my hand under the fuel lines that split and enter right before the carbs, you'll know if its leaking there pretty quick and this area is really common because the orings in that area start dry out after about fiveteen years.. ive had had to replace them on almost all my older blades.. and also alot of it will evaporate because it will fall on the motor first and unless you have a full on flood of gas going it will dry before it hits the ground.
im not sure what else i can add.. if you do end up pulling your carbs and cleaning them, i would right down the number thats on sides of the "main" jets.

Cool thanks for the tip with Photobucket! Here's my first attempt at it too.

Ran it for about 3-5 minutes before I took the tank off and plugs out. Just know that they look darker in the pics then when I took them out. Took the pics right away per plug. But they do look to be a little rich and were slightly damp around the threads when pulled.

WilliePete's Library | Photobucket

Ok well i took off the carbs to check the jet needles and found out that they dyno jet stage 1's. I will be adjusting them one notch up to lean it out a little and see what happens then.

Also added some more pics to answer your request earlier of what my vacuum line and such look like under the tank.

The PO installed the inline gas filter but I did change that out and replace all the gas hose segments about a month ago. The air vent tube terminates into nothing like my 96-98 service manual (in PDF format) shows. Also you can see the petcock diaphragm vacuum line is blocked off as the diaphragm needs to be replaced and leaks fuel if not plugged. Over then that I do not see or feel any fuel leaks.

CBR Troubleshooting Photos by WilliePete | Photobucket

Attachment 29113


That's a problem. Probably THE problem. That should be hooked up to a connection right underneath the #2 carb boot. That's what is going to regulate fuel to the carbs properly. Replace the diaphragm because if it's leaking that bad - it means there's no vacuum lock - it's basically running the bike on PRIME - ergo terrible fuel mileage and running rich.


What happens when you take the tank off the bike? Does fuel pour out of the petcock? How do you stop the flow?

Just got everything back together minus the tank. Seen your post so went and took a look for the vacuum line as you said. Mine is located under the #3 carb boot. Then took a look at the petcock and cover set again a bit closer. As you can see by the pictures below I would def say the diaphragm is bad.

Petcock With Cover Set Removed. Photo by WilliePete | Photobucket

Cover Set, Looks Like Something's Missing.... Photo by WilliePete | Photobucket

Also I have to siphon the tank before I pull it or gas goes everywhere. Prob just gonna get a whole new petcock set because even the valve is sketchy/sticky when switching from ON to OFF to RES (back and forth and such).

Oh, damn - I forgot that part/didn't re-read it. Then that's definitely it. Your bike is running on PRIME because of the diaphragm. Leads to the richness you see on the plugs and the bad mileage

I agree - a new petcock would be a good idea. You should be able to find on ebay for a reasonable price. If there wasn't the issue with the handle, I'd say you should just remove the rubber and carb dip it to clean all that out. But all things considered - just get a new one. It's less of a hassle to pull it out of a package that the USPS drops off at your door than it is to replace everything needed and clean it.

But yeah, when you pull that vacuum line off - the petcock shouldn't really leak at all. That's why they don't have an "OFF" turn on the petcock handle, because it needs vacuum to flow.

Thanks (everyone) for the help and input!!! I will give and update to this issue once I get the new parts in and put on.

this is why i love this forum.. many people have been where you are and with out all the people who chime in this would probably have ended up being an expensive fix, but just slowing walking through everything with everybody makes this forum priceless!!!

def get to a point where everything is back together and let us know hows its going..
i might also have your manual i think you said its a 99, ill check my computer, just give an email and ill send it over..
jay

I think you'll also find that the bike rides a LOT better too. Carb'd bikes are pretty sensitive to the vacuum leaks.


But yup - that's why I love the forums. Someone has always had the issue you're having before. Sharing knowledge about it is being a good biker.

Well took longer then I wanted but here's my update. Ordered in a new petcock assembly and installed it about 2 weeks ago. Instant difference for the better. Weather moved in and limited riding/adjustment time so its still not perfect but it is a whole lot better!!Just need to fine tune the carbs yet and should be good to go from there!!

A new issue has put up now. Its a minor one but still a issue and will start a new thread for that when I can.

Again A BIG THANK YOU to all for your input and help!!

Right on man. That's part of it when buying used bikes. A lot of time is spent correcting others' mistakes - whether its the questionable shop they took it to, or a roadside fix originally meant to be temporary that turned into a more permanent fix. Every bike will have it. It just happens.

Glad you have it sorted. Can't wait to help you fix your next problem - and get that bike back to its former glory.