So I recently picked up this bike. I've been told with receipts that the bike is a 637 big bore. I swapped the plugs with ngk iridiums last week but was told that was stupid and will be putting it back to regular ngks. The bike had been sitting while the previous owner wasn't tracking it for awhile (wasn't quite street legal and kinda isn't still but i ride it) and the last track day he did said was leaking some gas he thought by a stuck float or something. I didn't experience that issue.

The bike has a K&N, question i've got about that is from what I was reading this decreased hp on peoples f3's based on dynos... but is that because the bike wasn't tuned after putting it on and just run or what? I'd like to see references about that

The bike also has a full exhaust and chopped yosh pipe i believe

So issue i'm having, noticed it on the track day but i'd get a hesitation or stutter up at high rpms. the track day was 80* ish air temps maybe a bit more

The bike was still doing it after new plugs at the dyno (sorry for the crappy picture at the end but you can see how lean it gets, i had to leave early before the printouts) 91rwhp

The bike seams to love cooler weather, today when it was 65 the front just loves popping up in first and i don't notice the hesitation as much.

Step 1/advice I'm guessing is disassemble and clean carbs?

Is there a particular issue I should look for?

I can have access to the dyno/sniffer if need be to better tune this but not quite sure where to begin

 

If your run is the red line, it shows a dip in the power band that relates to the a/f mixture going up over 15:1. That would be rich at that point. The a/f graph in red then goes lean at the top end. 14:1 is considered the optimum a/f ratio. Cruising can dip into the mid 13s for better milage. So, looks like the taper of the needle is pretty rich. But it looks as though the lean condition at the top end is due to small main jets. Maybe up one size.

Cool air is denser and that would offset the rich condition in the mid range. You pop wheelies because you are making more torque and horsepower in that area in the morning or when it is cooler. You could also drop the needle by raising the clip one groove on the needle top.

 

sorry but I think you're mistaken. It's A/F not f/a it's running lean

 

Doh!! You are absolutely right. I got it bassackwards. The leanest part is in the upper mid range and it runs rich at the top end. Sorry. Need to put my glasses on the right way next time. So, leaner one size on the mains, and raise the needle one or two positions. Raising the needle means lowering the c clip in the grooves of the needle.

Sorry for the mixup.

 

i've got more pics of the dyno on here that are a bit better
Bike stuff - Imgur



I pulled some of the air box off, and kinda did a ehhh maybe i'll just try seafoam or something and I poured a butload of seafoam down the fuel line to the point the bike was barely running unfortunately it's raining right now and i'm getting no traction near the top of first or second so i'll have to really test it out tomorrow or something and see if it helped any. otherwise it's probably time to shim needles

 

So i took it out today and it feels like when you gas it 1/5th throttle is fast then from there to full throttle is kinda not even as fast... i don't wanna say it bogs but it feels pretty much the same from 1/5th throttle to full, i'll probably end up pulling apart the carbs now. I don't see any air solenoids.. but i haven't dug that far yet. if stuff isn't dirty i'm expecting i have to mess with jetting... on that topic is it bad that it's getting cooler out now will that affect my jetting

 

So is this a problem, I kinda figured before I got in there that it would be like this given there is no speedometer anything like that. The hole in the airbox where a hose used to go was duct taped over, is there a better method for closing that hole?
does this change tuning at all

 

Taped over? Wow! You are only getting 1/2 of the air you need. Get another intake tube and install it asap. Plus, your carb vent is connected to the low speed air tube and you're missing some pieces. Here's a picture of what it should look like. Check to see if the ram air snorkel is still attached.

Some more research. The air tube should run to a solenoid that works on the pressure differential between the outer air tubes (not in your pic) and the tube you have connected to the carb tube. It will work the way it is, but may make tuning it properly a big p.i.t.a.. Google up your year (ex: 1995 cbr f3 air solenoid) and you will see some of your pieces have been removed. There are some other threads that cover the air solenoid and bypassing it on this site.

 

Mm crap they're pretty spotless...

I'm seeing a 130 marking on the center and on the side of the long one we've got a is almost call it an inflated K 40S

 

Now that's some of the cleanest carbs I've seen. Its a good idea while you have it open to write down the jets size and needle placement.