www.zxrworld.co.uk

Evening all,

Having searched through all 159 posts wherein jetting and shim are mentioned I've lost the will to live as I can't find what I remember seeing before in a post somewhere.

I'm trying to find the one where zimm mentions the setup he runs in his H model.

I have an 1990 H2 Jap import, 32mm carbs, 98 mains and standard, unadjustable needles, standard air filter and standard exhaust/silencer.

I've meticulously set the fuel heights the same, balanced the carbs and generally tuned it up. I have a flat spot between around 5-7k. Now, what I'm looking for is I recall zimm saying he has an H model and I seem to remember him saying that he has 102 jets in and shims the needles .5mm or so?? Is this correct?? zimm, do you remember that post? Might this setup work for me or ought I to get a set of 100s to try as well. I know each setup is different for each bike but wondered if this will get me in the ballpark, so to speak?

Thanks,

Mick.

hmm ...

what are the markings on your needles ?.. there are loads ..

i've had good results with the N77C H1 needles but dont know if the H2's differ.. also the jets i use are longer than the stock keihins, so i drop the fuel level (increase float height) by 1mm or so to compensate and lean out the midrange (12-13mm float height, 11-12mm with stock jets)

i wouldnt put bigger main jets in with a standard exhaust, #98's should be ok, and the mains dont have much say over the midrange anyway.

as you say though, all bikes are different.. try shimming the needles half a mm or so (richer) ..it can only make it better, or worse and if thats the case at least you KNOW it was rich to start with and can look at ways of getting more air in (new/performance air filter?) and maybe take the shims back out.

one final thing .. valve clearances can play havoc with midrange/flatspots/hot starting/cold starting.. if they havent been checked in living memory get them set first. 0.15mm in, 0.20 ex.

Zimm, thanks for that. My needles are marked N77C.

I just thought I had read a post where you said with Standard exhaust and filter you ran 100/102s. ???

I will try the shimming and see what difference it makes. Must say with the 98s in, after the flat spot it pulls well.

Mick.

' Mains dont have much to say over midrange anyway' Hmmm how far from the truth can that statement be??? Mains have 'a say' right from tickover to full throttle....just to prove it....try fitting a set of 130 mains and then see if you need the choke to start the engine?? 100% certain you wont. And regarding the jet length 'Zimm' if its within the float bowl and its flow isnt obstructed it doesnt matter one bit how long it is....we use either the standard or the hex fcr jets in both cv's and flatslides and dont go to float height juggling malarky...Carburetors what a simple piece of equipment when you understand them and how frustrating when you dont.

Trick question...........................and not a word from you roger


Can anyone tell me what the number of a main jet actually means like what does the 98 or what ever stand for ?????

hmm .. guess my language wasn't particularly clear ..

a flatspot between 5k and 7k (assuming that the bike pulls well at the topend) is most likely a needle issue rather than a main jet size issue

changing mains obviously affects the a/f all the way through the range, but it'll move the whole curve "as one" rather than introduce/fill in a "flatspot"

as for the jet length/float height thing ... it works for me ... the differences are small, and only really affect the low-midrange throttle response not particularly important or noticeable on a racebike.

cargo,

#98 jets = 0.98mm