Help needed with carb tuning theory

Hi guys, can anyone point me towards a link on carb tuning theory? I have a 94 cbr 900 with a custom 4 into 1 system, head porting and I will be running pod filters. I recon this will have screwed the jetting and I need to find somewhere to start as I don't know much about carb tuning. From what I can gather I will need a jet kit too.

any info would be appreciated

http://www.factorypro.com/

Find the section on CV Carb Tuning. Read it. Print it out and read it a
gain.

[ozzy1100]

then after u read it a 3rd time make note that u need to read it at least 6 more times
doh that just could have been me ....

sooo what are ya trying to say?? that i should read it?

Or you could simply buy a Factory Pro kit and fit it with no idea why or even if it's working right.

Your choice.

Just kidding:) Thanks guys. I will study this well.

Also just wondering if there are different types or makes of jet kits for the early blades? I know dynojet is the most popular but I can't seem to find anything besides a stage 1 kit. From what i can gather i will need at least a stage 2.(according to dynojet info) Like I said its got head work, full 1 into 1 exhaust and no airbox. Is this just marketing and a stage 1 will do?

Someone might clarify the difference between the 3 stages of jet kits?

Thanks heaps

[Dynomutt]

The Dynojet stage 1 kit is used in conjunction with the stock airbox with a free flowing airfilter such as K&N, BMC etc. The stage 3 kit is usually used with the airbox removed and the carbs fitted with individual filters. In some Dynojet kits you will get both stage 1 and stage 3, with the latter having larger mainjets than the stage 1, the needle however remains the same for both. With some bikes only a stage 1 kit is available as they don't tend to run well with the airbox removed, case in point being the ZX9R C/E/F models, these bikes also suffer when the fairing is removed as the ramair ceases to function correctly, this is easily remedied by running two short lengths of hose from the float chamber vents into the airbox, and slash cutting them to face towards the airbox intakes, thus equalising the pressure inside the float chambers in a similar manner to using pitot tubes on a blow through set up. What bike are you trying to get set up?

Thanks for that, I am trying to jet a 94 cbr 900rr. I have been told that they don't respond well to removing the airbox but I must now do this due to moving the battery under the tank. I cannot find more than a stage 1 dynojet kit so I am worried about this. Does it have to do with intake charge resonance or float pressure like the zx9? Is there any way around this like plumbing flexable tubes of a certain length to each velocity stack?

So the difference is just main jet flow between stage 1 and 3?
Would yu recomend the factory pro kit or the dynojet stage 1 kit?

Thanks for your help

Less headaches with Factory Pro.

Here's the part number: CRB-H21-1.0

[Dynomutt]

The CBRs don't like not having an airbox, however that said, these engines have been used in some kit cars here in the UK, and there is a filter set up available for them which mounts across all 4 carbs and is one giant foam filter element, using this with a DJ stage 1 kit and then tweaking the fueling on the dyno would sort it out, I've used this on a blade chop thing that my friend in the unit next door to me built for someone which had a top tube running through the space where the airbox should be. The difference between stage1 and stage3 jets is usually about 20, so if you had stage1 jets of 100 you'd expect to have around 120/125 for the stage3 usually when fitting individual filters the main jet needs to be increased by about 20% to 25% depending on the carbs used. You could always ditch the carbs you have and look for some flatslides and run them with short velocity stacks, both the YZF750SP and the ZXR750SP came factory fitted with Keihin 39mm FCR flatslides, these are easily respaced to suit whatever spacing you need, and work well with short stacks, I'm using a set on a 1066cc FZR1000 Genesis/EXUP hybrid engine which revs to 12500rpm 2000rpm higher than the stock bike, and these carbs give great response and work very well, although if you can find a set of Mikuni TDMR downdraught flatslides either 38mm or 40mm then grab them as they are a much better carb especially when fitted with the Yoshimura MJN multi jet needles. I'll speak to my friend next door when I return to my workshop on the 4th of Jan, and see if he still has the details of where the blade foam filter came from, as it is only about 60mm high and about 120mm wide and fits between the frame rails easily.

Thanks very much guys, and yes that filter sounds perfect. I would love to know where to get one. At this stage I think I will keep the stock carbs and go with a factory pro jet kit.
I emailed Marc Salvisberg from factory pro and he said with the foam filters 150 -160 main jets are the go. I have no experence with this but have to start someplace.
Thanks for your help

Hey Dynomutt, any word on that cbr900 airfilter? I'm very keen to find one like you mentioned.
Thanks very much

[Dynomutt]

Yeah, I spoke to my mate in the unit next door, but he cn't remember who the filter cme from. It was something to do with fitting these engines in kitcar/hill climb cars. If you google blade engined car it should take you to some sites which would have info. You could always try Demon Tweaks automotive catalogue rather than the bike one.