I just got my second CBR 600 f2 and this bike is in ruff shape but for $400 bucks who can complain? Now the issue Im having with it is, It will not go over 7k RPM in 6th gear. 1-5th Is fine bounces off the rev limiter but as soon as you gear up into 6th it just bogs down and I have to feather it to a sweet spot which is right between 6.5-7k RPM and wont go over that. The previous owner told me the carbs just need to be synched, But before I go out and buy myself a $100 tool and it might be something even simpler what should I do guys. I just spent my whole pay check on the bike, and everything I could think of to make it look pretty off ebay (Will Post Pics Before and After) But I have to get it running right. Any input at all would help!!! Thanks In Advanced.

 

Ok- so in every other gear the bike runs/pulls with no problem? Nothing should be different in 6th that would cause that drastic of a throttle response/drivability issue.

What is the bike doing once you get it to 7K in 6th when you try to go faster? Just bogging, no popping/backfiring or clutch issues?

Look at it this way - with a 15/43 gearing, in 5th gear your bike should be doing about 6100 rpm at 70mph. Click up to 6th and you should drop to about 5500 if you maintain that 70mph. I can't see the rpm change causing the bike to start stumbling all over itself, also if you were to accelerate to 77mph in 5th, then shift to 6th, you should be running about the same 6100 rpm you were doing in 5th at 70. If the motor runs fine in 5th, it should run fine in 6th, as long as you're maintain appropriate speeds for using 6th gear.

If you were to shift to 5th at about 3000 rpm, you would be doing about 35mph. If you can get the bike to pull in 5th from 3K to redline - there's not a problem with the carbs. You're putting a load on the motor/ignition/fuel supply that requires the carbs to transition from low to high speed jets and deliver power all the way up. Motors don't care what gear they're in, all they see is a load. You can't load the bike up much differently doing a pull from low speed up to redline in 5th than you do in 6th.

If I'm speculating, I'd have to say you've got something wonky in the transmission that is putting a ton of resistance into the drivetrain. If it were fuel delivery or ignition, I think you'd see the same thing in a 5th gear 30mph to redline type of pull, or symptoms of it at least.

 

The bike aslo does it in 5th gear, Just not as bad. So Im cruising along 1-4 No issues at all what so ever. Then I shift into 5th gear rev up to about 6k and starts slowing down not instant but you still feel the power loss then it will not go higher than 7.5-8k rpm just bogs down acts like its running out of fuel. It doesent suddenly jump or anything it just slows down, then I shift into 6th and same thing I can hold it wide open and it will not go over 7k rpm and then slows down to right around 6.5k RPM and wont go over that. Ive changed the plugs, cleaned the air filter, Cleaned the carbs, and changed the fuel filter, My next step is fuel pump, and voltage regulator those are the only other things I can think of it. And its not when the bike is under a load because it will bounce off the rev limiter it 1-4 which makes no sense at all. I hate to say this but if this doesn't work I'm going to have to take it to a shop which I ****ing hate doing because I'm fairly mechanically inclined...

 

No fuel pump on an F2 - so one less thing to check.

I'm starting to think fuel starvation - sounds like you're on the same path. In 4th or lower you probably don't run the bike up near redline and hold it there for very long like you might in 5th or 6th, just due to acceleration and top cruising speed.

Even the pull through the lower gears while shifting might be sucking the fuel out of your float bowls, and you don't notice the problem til you're cruising in 5/6 gear.

I'm curious though - try setting your petcock to the reserve position instead of the normal run position and see if the problem continues. If you've got a semi-clogged screen on the normal fuel pickup, you might be running your carbs dry there, the reserve pickup might not be as bad. something easy to check at least.

Also - check the vent lines for your tank - if clogged, kinked or obstructed, they might be causing your tank to mildly "vapor lock" under WOT. It basically doesn't allow air into the tank to replace fuel being sucked out, and has been known to cause bikes to gradually lose power and quit running very similar to an "out of gas" situation.

Check the vacuum line running to the petcock from Cyl #1 to as well - if cracked or disconnected, your petcock won't be flowing fuel properly. Instead of a fuel pump, there is a diaphragm that is driven off of vacuum pressure to allow/cut fuel flow.

 

I dont know what I was thinking about a fuel pump??? lol but tomorrow Im going to try it with it on reserve and with the fuel cap open maybe Ill get lucky and I already replaced the vacuum line from tank to carb 1. Here is something else for you to think about the previous owner spray painted the entire bike black he didnt mask anything off, If paint where to get into somewhere and really mess something up where should I look? Thanks for all your help Im lost. Ive been searching around and I have found that a lot of the GSXR bikes (600's) Had this same exact Issue down to the T. They all claimed they fixed their problem by swapping the T shapped vacuum lines that cross over from the air box I believe. Im also going to try and put dryer sheets around the snorkle holes with a rubber band and maybe thats what the problem is. When I pulled the jets I couldnt find a # on them anywhere Im either assuming its a very cheap jetting kit from china or its factory with markings? Let me also mention the wiring harness is all jacked up I havent had time to really sit down with a diagram and trace everything down, but I will soon got this weekend off I will update you tomorrow night work 3-11pm. And again thanks for all your help I called the mechanic shop they wanted $120 just to look at it with no guarantees lol. One other thing I really have to mention when I pulled the carbs off, I looked down into the engine and could see the valves 1 2 3 4 cylinders. 2-4 where spotless but number 1 looked very (dirty) I could say like it was just covered in carbon build up. Could this be the issue? And one last thing I can hold it down in 4th gear and bounce off the rev limiter for miles with no hesitation or anything, I would think thats at least close to the same fuel supply as 5th gear running 7k rpm? correct me if im wrong please.

 

Doewnload the manual and make sure all the vacuum lines and hoses are going where they should be going. I found one summer that I was having big issues with my bike. I would be driving down the highway and it would keep stumbling and actually stall at times. this was all after I replaced a bad float. It would start fine and run through the gears then F up on the highway. Finally one day I went to pull the tank yet again and looked under as I did. Noticed I had set the tank on a fuel line and pinched it a little. I adjusted the hose and the bike never had an issue after that.

The F2 is about as basic as it comes. Carb and air without any computer control to air or fuel. As long as the carbs are adjusted corectly then you should be good to go. You mentioned that you synced the carbs. Did you also then go back and adjust the RPM at idle afterwards? In order for the bike to run correctly, not only do the carbs have to be in sync, but without the throttle adjust **** turned, you should be maintaining a steady minimum RPM. There is a procedure on doing this outlines in the service manual. There is more load on the engine in higher gears than there is in lower gears and so it would be easier for the bike to rev. you may be getting too much or too little fuel which would easily cause sluggish performance.

If valve #1 was dirty then there is a chance there was something wrong with that carb, or you have a cylinder problem there. You should be able to clean it off with carb spray while the bike is running. Also, you can check the plugs as you go to see how it is running after your changes.

 

It had factory jets I bumped them up 140/40 and it runs amazing guess it was starving for fuel...

 

I really hope that you set the carbs to specs as I mentioned, otherwise you are just masking a problem. If you already had then I'm happy it worked out, though it doesn't make sense that the bike wouldn't run in 5th or 6th past 6k even on factory jets.

 

Sounds like maybe he had a plugged jet(s). I had main jet problems and the bike would only rev to around 5 or 6k on the pilots. Made it home and found three of the four mains had come loose due to lack of proper tightening. On my part.

 

the jets were a little dirty but not plugged. Before I ordered the jets I replaced the rear sprocket with a 49 from stock 43 tooth. and the problem almost went away! It was very confusing I ended up only changing the main jets because it idled fine... After a little tinkering with idle air screws it runs fine...