Hello all,

I have a 1995 CBR 600 F3 that I just started after the Minnesota winter. This year my bike seems to work fine in gears 1-3, but as soon as I shift above 3rd, I lose all throttle. It's as if it's not getting any gas. If I hold the throttle open, I will accelerate after about a 3 second delay, but I cannot hold a constant speed.

I had a friend look at it and he doesn't think it's the carburetors, but I'm willing to listen to any suggestions.

 

Sounds exactly like a fuel issue -- dirty carbs or clogged fuel filter. Did you leave last season's gas in the tank all winter?

 

A minimal amount of gas was left in there. I ran stabilizer through it before I put it away for the winter too.

 

why would the transmission have anything to do with it though? shouldn't he be having the same problem in 1st/2nd as he is in 4th?

 

This is what my friend thought. He figured if it was the carbs, I'd always have the problem, not just in the higher gears. He checked the carbs anyway though and said they were good. He called around to some motorcycle dealers and some of them thought it might be electrical...

 

It prolly doesn't. It's more likely a matter of speed or throttle position when he hits the issue. Just happens to notice it when he kicks into 3rd.

Also check the fuel pump while you're at it. The way the carbs work on the F3, the fuel pump is "on demand", meaning it's only on when necessary to keep fuel in the floats. At higher speeds, gravity isn't enough to keep the float bowl filled so the fuel pump kicks in. If it's not working (or in a lot of cases, it's missing), you can get a bog issue as well

 

My bike would not rev past 10k in third and 8k in 4th and wouldn't do anything in 5th.

I had thought I did the PAIR mod when really I took out the direct injection air valve and pipes. This fixed my mistake:

Float Bowl Vent Mod

Tips

Routing the float bowl vent tube to the airbox guarantees the positive pressure you need in your float bowls to get the fuel up through the main jet, emulsifier tube and past the needle.

I also shimmed the needle. It's all here:

https://cbrforum.com/forum/cbr-600f4...-build-121968/

and here, last few pages:

"New" track bike!!! - Custom Fighters - Custom Streetfighter Motorcycle Forum

I can't say for sure that this is your issue as you probably weren't a dumb *** like me, but you never know.

After "fixing" my mistake, the bike instantly ran properly.

Start at the source though...make sure your fuel lines aren't kinked...check the fuel pump and filter. Check the tank vent lines...

 

I run gravity feed and only notice bogging at very high rpms. I dunno that the fuel pump is the culprit but you could always try a gav feed and see how it goes.


-DrAwkwarArD I was looking at this post the other day, next time I have my tank off Ill have to try this out. Im just a little confused about how the float bowl mod is different than just remvoing that air solenoid or pair valve or whatev? (write up plz?)

 

Pair valve mod, as far as I'm concerned removes the PAIR valve completely from the system and runs the crank case breather to a T connecting the reed valves together. You can also connect the reeds via a coupler and run the crank case breather to your airbox (which isn't necessary) or to an independent small filter located somewhere convenient.

The float bowl vent mod takes the Direct Air Injection valve and all of its associated hoses (the ones that tun up into the nose of the bike) and gets rid of them. You then take one of the hoses from that system and run it directly from the float bowl vents to the front hole on the airbox and make sure it's sealed well. That ZX7 link is essentially exactly what I did, except I routed the crank case breather to the reeds in a T.

Next time I have the tank and stuff off I'll take some pictures for you and put this in my build thread.

IMO, this has worked wonderfully for me and has allowed me to tune my carbs based on spark plug color. I can now just shim the needles or change mains until I get the color I want to see on the ground of the plug. Pretty simple process.

If you want to do the mod, shoot me a PM and I'll sen you my number and you can call if you have any questions.

 

The higher the gear the more power you need to gain RPMs. So if there is a fueling issue it will show up more prominently in higher gears. Just like pedaling a 20 speed bicycle up a hill in high gear.