TOPIC:

Hi all,

I have converted my bike from injection to carbs, and now at least it runs... The question is what size on the main jet I should use. Right now I am using 127,5. The carbs are from a z1000j with a cv-thingy on the side, have separate pods and the exhaust is stock.

What happens is that at full throttle, when reaching approximatley 6000 rpm the bike bogs, or "protests", and only reluctantly continues to accelerate... Could this be resolved by going up to 130 or 132.5? It doesn't run great on low- and mid-range but no sputtering or bogging at least...

Tips or knowledge would be greatly appreciated..!

145 ~ 160 mains 165 when you get the header pipe
lift the needle too it'll help mid range

145 to 160... phew, sounds like it will cost a few bucks (or kronor, since i'm a swede..)to get my precious running decently... And thanks for the mid-range tip! By the way, "Header pipe" = Aftermarket 4-1 exhaust?

kawaduce wrote:

"Header pipe" = Aftermarket 4-1 exhaust?

yes

do you have micro drill bits? drill them a little larger at a time but remember to file the number off of it so you won't forget it is modified. if not I have extras that I can ship to you u.s.p.s. they have very reasonable rates. trade for homebrew stein or cool smoking pipe something sweedish and cool? Idunno??

header is slang for a 4-1 pipe

pods create a intake velocity glut that is noticable just off of idle. as rpm's rise and the needles kick in it goes away.

I will go to my shop and measure a jet and give you a measurement for presicion hole size

trippivot wrote:

pods create a intake velocity glut

Might have a language problem here... What is a "velocity glut"?

And yes trippivot, measurements sounds supreme! If we later end up in any kind of transaction-situation, I am certain I can dig up something swedish that have some coolfactor... Polarbear tooth, maybe?

Those are BS34s and may not have adjustable jet needles but the jet needles generally don't need to be shimmed so #140 main jets and #42.5 pilot jets. If you are using the stock #37.5 pilot jets, the bike is likely difficult to start. On my test bikes, using the stock #127.5 pilot jets, I can pull about 5K rpm, with #132.5 main jets, I can pull about 6K rpm, with #135 main jets about 7.5k rpm, with #137.5 main jets, I can pull redline but still not quite enough and with #140 mains, will pull cleanly to redline. I like using the leanest main jets that will allow me to pull cleanly to redline as it makes tuning of other circuits easiest. You can get away with #40 pilots and I would recommend them if your spark isn't great as you MIGHT foul plugs at idle with #42.5s unless your spark is good.

Post edited by: wiredgeorge, at: 2006/07/10 09:17

Thanks for the advice, WG! Will start on 140 and go from there (found a set of 140's hidden away in my garage, not Mikuni original though).

I do have adjustable jet needles, might it be a good idea to follow trippivots advice and lower the clip?

When I rode the bike to work this morning it suddenly started to "backfire" or "cough" in the carbs..??!! Possible air leak or jettingproblem?? The airmix screws are 2 turns out. It disappeared when the enginge had warmed up...

Well, lots of new questions... should maybe start a new thread...

This link is from the "link" section listed under "SITE FUNCTIONS" and is good reading. It's helped out a lot of people here, myself included.

www.factorypro.com/tech/carbtune,CV,high_rpm_engines.html

If you have adjustable jet needles, raise them by lowering the clip to the 4th slot. You will then be able to use #40 pilot jets and might avoid flat spots. Most BS series carbs have non adjustable jet needles and rather than shim, I prefer to go up two sizes for the pilot jets which helps reduce the possibility of a flat spot. The Factory Pro advice for main and jet needle settings is very sound but their advice to muck with the fuel level for TUNING isn't what I personally would recommend. I recommend you set the fuel level at the factory specified level and leave it alone and not consider it carb tuning. I would also like to point out that they don't include pilot jets in their jet kits so have you twisting away on a mixture screw using pilot jets that WILL BE TOO SMALL if you are using pod air filters. It is IMPOSSIBLE to tune BS series carbs so the bike will start easily and warm up quick if you don't go with bigger pilot jets when swapping out the stock airbox for pods. Also, their advice on setting the main jet relies basically on trial and error. I have done enough trial and error on main jet settings for the BS series and my recommendations are basically made from my personal observations. I test with stock engines so if you have a highly modified engine and use a high flow petcock, you MAY need larger main jets than my recommended #140 but that size will get you REAL CLOSE if you have a fairly stock 750/900/1000/j style 1000.

CoreyClough wrote:
www.factorypro.com/tech/carbtune,CV,high_rpm_engines.html [/quote]

Yepp...have read it, and has been of help!

And WG, what can I say but deepest respect for your knowledge and willingness to share! My bike is pure stock except the pods. And I would prefer not to have pods, but I don't want to ruin the "stock-box" I have by carving in it if I one day decide to re-install the fuel injection (missing too many parts right now). Thinking a z1000j airbox might fit? Well, when I can get my hands on one I will find out !

Once again, thanks all!