KR-1S.co.uk Forum

i popped my shock last week so thought id put an r6 shock in...easy mod to do but the airbox is a pita
the bike went from a smooth power delivery to stuttering as it hits its band...ive chopped out at least half the original volume and im sure its too small to begin with..what volume should the airbox be im sure its on here somewhere but i cant find it.
running with the airbox lid up at the mo....

did anybody else find this a problem after modding the airbox?

Everyone makes them bigger when modding them, I can't remember the formual for the idea size but it is a lot bigger than the standard which can't really supply enough air anyway.

One mod is to put a cold air scope from the front of the bike which will require you to drop the radiator an inch and then run a smooth large rectangular plastic tube (mine is approximatly 1" x6" wide) from above the rad and into the lid of the air box (I have then closed off the old intakes). This allows a good high flow of cold air into the box and allows you to keep the filter in.

If your making a new airbox then make it as large as you resonably can and if your an expert, you can design it so the sound waves which build inside the box will match the frequency of the engine at the maximum revs. The idea is that the compression wave of the sound will be entering the engine in harmonly with the intake pulses at the point in the rev range where you want maximum power. This gives a free increase in air flow/density and so an increase in power.

I'm looking at mine at the moment, Mr B is right- the standard box is not exactly huge and fitting the R6 shock just about halves it.
I'm looking at moving the battery like Elf has and using that space, mine also runs premix so I'm hoping to use the space left by the oil tank to increase airbox space/ locate battery.
I'm only working with cardboard at the moment, as soon as I have something worth looking at I'll post up some pics.

Mike

P.s. Welcome back Mr B

Install some power jet kits, cure the over lean condition for good.

I guess it depends how you mod the airbox. I modified mine now so that the bottom is flat, obviously lost some volume and was expecting a drop in performance, but it still feels quick and goes well. I also have non standard spannies too (Nikions). Worth checking you jetting too

Cant you just fill one with water and then pour that into a measuring recepticle to get the volume?
Cheers
AL

TwoStroke Institute wrote:Install some power jet kits, cure the over lean condition for good.

I've looked at these in the past, do you mean something like these? http://216.194.105.243/powerjets.htm

Out of interest do you know just how do they benifit the fueling?

make one from scratch or extend the std one. i opted for the former and although it aint to barry's (bb plastics genius) it should work nice. taken months of restarts ect and a lot of trial n error but volume has prob doubled usingh the tank as the lid and partially using the spars for the sides. still need to make ducting (one of the kr1 frame drawbacks-thick h/stock bracing). all because i had no carb/airbox rubbers to fit 35mm carbs! will use the std one as a backup if i need to. think a std box is only smallish, about 8-10l id imagine. not a bad airbox but on the limit already in terms of volume, any smaller and it could effect air hungry tuned bikes? maybe you could jet round it bung?

Yep that's the ones except I use either the Mikuni soleniod cut or plain 'dumb' powerjet kits from Allens.
Benefits are that with the needle/needle jet/main combination is fine when everything is within the design parameters.When you introduce(in this case) much more available air, either fueling on the needle/needle jet combination or on the main will be correct but not both.Blubbery mid if the main is correct and beautiful mid and it cutting out/jerking along on the main.Enter the PJ this when intake velocity is sufficient sucks fuel from the bowl dumps it into the front of the carb.Gives an extra circuit to tune, usually works >3/4 throttle.

TwoStroke Institute wrote:Yep that's the ones except I use either the Mikuni soleniod cut or plain 'dumb' powerjet kits from Allens.
Benefits are that with the needle/needle jet/main combination is fine when everything is within the design parameters.When you introduce(in this case) much more available air, either fueling on the needle/needle jet combination or on the main will be correct but not both.Blubbery mid if the main is correct and beautiful mid and it cutting out/jerking along on the main.Enter the PJ this when intake velocity is sufficient sucks fuel from the bowl dumps it into the front of the carb.Gives an extra circuit to tune, usually works >3/4 throttle.

So it works like an accelerater pump?

.

or theres this mod - not even practical on a KR tho...

http://tinyurl.com/ceetpf

...looks like a little needle valve to control how much additional fuel gets drawn through pipe nozzle by venturi effect.

NEXT question... when is someone going to fuel inject their KR?

a decent programmable EFI will do 8 or 12 cylinders to 15000rpm - but four should be enough - in pairs running sequentially. You'll have more flexibility in airbox design because you could run the throttle bodies true downdraught.

No need to wait for EFI as Smurph already has done it on an RZ 350 and a fellow here is close to completing his RZ 500.
LINK

No the power jet ONLY works when the choke air velocity is high enough, so it by passes the main jet.

Good description HERE of how a power jet works(calls the external fuel jets). Sums up what I was trying to get across above

TwoStroke Institute wrote:No need to wait for EFI as Smurph already has done it on an RZ 350 and a fellow here is close to completing his RZ 500.
LINK

No the power jet ONLY works when the choke air velocity is high enough, so it by passes the main jet.

Good description HERE of how a power jet works(calls the external fuel jets). Sums up what I was trying to get across above

Thats very interesting. Thanks for the link. By the look of them they are simular to what is on the PWK airstriker carbs?

What kind of size jet would be a good starting to start to tune in a pair of these on two PWK35mm carbs?

The link you posted the power jet has a screw and a needle so there is no jet as such, the Mikuni kits have a 100,80 and 65 PJ in the box. A 100 Mikuni PJ is equal to a 1.00mm hole so you can hav any jet size you want provided you can find the drill.
Jettting is usually 1/4 to 1/3 of the size of the main. Say 300 main no PJ then new main will be 225 and a 75PJ