Hello all, I recently acquired a beautiful 1994 cbr600f2. It came with a V&H slip on, stock air filter and stock jetting. The bike ran great but had a noticeable hesitation during the off to on throttle transition in the midrange (5 - 7 K). Not a big deal at all though, my friends didn't even notice it. Anyway after a little research and thought I decided to shim the stock needles with some little washers I found at the hardware store. I measured the washers to be 0.025 inches thick with my micrometer. After installing the washer/shims, bingo, smooth off to on throttle transition! This makes all the difference in the world when you are leaned over in a turn and begin to feed the throttle back in. overall it feels about the same power, just a little smoother and more responsive in the midrange, exactly what I wanted. If anyone else has or wants a slip on and doesnt want to go with a jet kit, shimming the needle will be the cheapest easiest way to maintain proper midrange carburation. By the way I am about 2.75 turns out on the pilot and running 100 % stock except the V&H slip on.

 

I've actually heard from a variety of experienced former F2 racers that this was infact the most affordable trick go get the bike working the way you want it.

So I advocate that this is a legitimate solution to many bikes out tere... although a slightly larger pilot jet in conjunction with this has been known to deliver even better results!

 

This is definetly the old school trick before the days of carb kits. Anyone who wants to do this just remember, it depends on the ambient air temp as well as to how well your bike runs, so where one shim worked in thie case, if you are in colder temperatures you may need more shims, or a larger main jet. Ect Ect.

Now back to the thread at hand, definetly an excellent diagnosis and carb tuning done by you, just out of curiosity how is your top end, 7k to redline? Does it pull the same with the bike cold as it does when warmed up?

 

Top end rocks. Pulls hard and strong right to the redline and sounds glorious doing so.

Midrange is very crisp. My shimming of the needle definitely made a difference in the crispness here, instant response to any throttle input. I ride the twisties in the 6 - 9 K rpm range all day with a smile on my face.

As for the hot and cold top end comparison, I don't really go into the top end until the engine is fully warmed but on the rare occasion I have it seems to feel about the same as when fully warmed. (No, lean symptoms when cold and no rich symptoms when fully warmed)

The amazing thing about this bike is how smoothly it pulls from as low as 2500-3000 rpm. It feels fuel injected. The bike can take full throttle at all engine rpm (2500->) with no breaking up or hesitation.

I actually own a dynojet stage one kit for this bike but can't see a reason to mess with the carburation right now. I dont care much about gaining a few top end hp, what I am interested in is smooth, crispy and torquey throttle response from 6- 9 K, where I usually am during my sane yet spirited backroad blasts. And this machine delivers as is.