Newbie here, I need some help. I just bought a 98 cbr f3 with 18,000 on it not running. I got it for a steal and cleaned the carbs and it worked great for two weeks. It started getting bad mpg so I changed the oil. It was good for a few days now it is down to around 55 miles on a full tank. I am going to change the air filter but I can't imagine that would be the sole problem. I am not riding hard. So any ideas would help thanks in advanced.

 

Does it run good, power across the whole band? No stumble spots in the rpm band?
If you crack the throttle does it pull? or brief hesitation before responding? What was your milage before? How many miles ago was that milage? Did it happen suddenly or did you gradually noticed it?

What do you consider, "cleaning the carbs"? Did you pull all the jets? Did you set the mains back to stock "turn out"? Sync the carbs afterwards? Adjust the idle after that?

I'm not trying to be sarcastic with this line of questions, actually trying to establish a 'base-line' of where the bike is now. If you post up some of the answers, we can probably get you headed in the right direction.

As is, based on what you've said so far, I'm thinking carbs are where the flashlight needs to be pointed.

Ern

 

Any gas in the new oil ? if so sticking float valve(s) , gas is slowly draining into the case

 

Is it running on all four cylinders?

I was getting ~80 a tank when mine was running on two.

 

Have you got a leaking fuel tank? Can you smell petrol when she's been standing for a while?
55 is awful. You need to sort this out fast.
Answer Ern's questions and you may be redeemed.