so i decided yesterday i was going to take the carbs back off and check out the intake boots. before then i was thinking vacuum leak because the idle wasnt steady, it was popping out the intake, and it would not idle without the choke on (very lean). i sprayed carb spray and it looked like the problem was coming from the intake boot on carb 3. assuming i had a vacuum leak at this point i take everything apart and when i go to examine all the boots they all look perfect!

let me state this: i DO NOT have a stock air box set up and the crank case ventilation tube on top of the cam cover is open to the atmosphere right now. i realize this will cause a slight leak, but i didnt think it would be that big of a deal since it is vented back to the intake anyway. knowing this i kept the tube close to the inlet on the carbs so that it would be CLOSE to the stock setup.

where else could i be letting in unmetered air besides the intake boots and the vent tube? i am completely lost and am unsure where to start looking.

 

........... ya nailed it...........there's the problem.

She'll never like that

 

so even if i vented the crank case back into the intake somewhere, it will still act up? i dont see how the air box itself would cause this problem. i have no intensions on putting the air box back in unless i had to and planned on putting individual filters on all the carbs. i know there is a big debate on the low pressure area inside the fairings causing it to not work as well as an FI bike, but i was thinking if i jetted it rich enough that it would run just fine with an almost completely open intake.

 

I used to dragrace an 88 CBR1000F. Before switching to FCR carbs, I tried making it work without airbox. It "can" be done, but takes ALOT of trial and error with tuning. I went up 3 or 4 pilot jet sizes (can't remember which). Ran 3 shims under stock needles and mains were in the 150 range if I remember correctly. I actually got it running pretty decent but bike didn't run much quicker than it did with airbox on it. The vent tube isn't going to bother you that much. I stuck a small K&N looking filter on it and hung it off side of motor. The FCR's really woke it up. With 1049 kit, slight porting of head, and the 39mm FCR's, it ran a 6.60 @108 mph in 1/8th. MPH was unreal for such an old bike. If someone made aftermarket cams for that model, I might've kept running it. She was a great ole bike.

 

what model of bike did those carbs come on? it might be something i want to look into. at some point i will be making a custom intake manifold that can handle some pressure, since this bike will only be n/a for another year or two.

 

You mean the FCR's? They are Keihin aftermarket performance carbs. Technically they don't make a set for the CBR1000's but do for the CB1000's. I made my own intake boots out of radiator hose, worked like a charm. No idea what's involved with installing filters. Mine was race only so I didn't use filters. Be prepared to break the bank, they are VERY pricey. I just bought a new set for Blackbird motor in my 900RR...1,300 bucks and some change. Also had a set of Lectron's on it for a while.

 

ooh boy, i thought they were replacements off another bike. probably not looking into getting anything that expensive. thanks for the suggestion though!

any ideas on where to start with my jetting to get the bike to run nicely with a damn near open intake? id hate to buy a stupid amount of jets just to trial and error myself to death. at the moment (bought the dynojet stage1 kit, am i stupid?) i am running the biggest jets that came in the dynojet kit which are 124s. the ones i pulled out of the bike, which i assume to be stock, were 122s.

 

You'll need ALOT more than 124's. I'd start first with the bottom end. If you're riding on the street, you shouldn't have too much trouble. I would start with 2 sizes up on the pilots and back fuel screws out at least 3 turns to start (if you haven't already, you can cut off the lil stubs on fuel screws with dremel tool). From there, trial and error with the needles (I'd start off in at least #3 position). Mains are gonna be worst part. Do lots of plug checks. I would say at least 145's. If you plan on buying jets new, go to www.jetsrus.com They are cheapest place I've found on the net to buy jets. I may actually have a set in the 145 range if you'd like to try them (pm me your address). Are you going to try and make individual filters? I started to do that years ago but never got around to it. I figured you could take the boots going to airbox and route them so they'd all be directed towards center of bike and find some pods that would go inside them. I'd definitely put something on there if riding on street.

 

Could your diaphragm in one of the carbs have a hole in it ?
If you're just running the bike on the street, and you want a bit more "off the line" why not go up a few teeth on the rear sprocket.
My friend the late Tim Wilkinson ran 15/46 gearing and there wasn't anything that would outrun him to 120MPH. After that he ran out of revs.
As for the jetting - these bikes run better with the original airbox, but it's your call..........and the std jetting is slightly rich anyway. I run a K&N, big bore exhaust and Dynojet kit 1, and she runs perfectly.............and is a 90 model.

 

i found a few places that sell cone filters that will go right on the intake side of the carbs and that's what i was going to go with. at the moment im running with nothing on the intake side, which i wont do once it is running correctly.

i might take you up on the offer for some jets, ill send you a pm shortly.

the diaphrams all looked good when i had the carbs apart. i also replaced the o-ring within it as well. i was thinking that i was going to get it running how i want it and up two teeth in the back as well. i dont necessarily want off the line, but i just want to see what i can do with the bike just playing with the intake and exhaust for now.