View Full Version : Carb jets
01-02-2006, 09:56 PM
Im wondering what the normal step up in jets is?
After fitting my new pipe its got a flat spot or pause in between changes at high revs.
Ive read the dyno kit trouble shooting guide and it says its probly running lean in the top end.Id already guessed that.
Ive dropped the needle clips one slot and it made it a bit better
so main jets is next on the list.
Ive been told up in increments of five.
Any body got any ideas on what mains i should be running.
Got dyno kit in it already(not sure on mains)
Moded and de restricted air box
21/4in pipe into 21/2in hot dog and back to 21/4
your onto it Damo,if ya raised the needle an thingas got better then concentrate on ya mains.Cant help ya on stage 1 jet sizes due to that custom pipe and modified air box.only real way is to hit the dyno,its definately a cheaper way of diagnosis.but if ya have spare jets then try increasing in 5's,sounds like its not far off the money but a dyno read should only cost about $55 without tuning.
02-02-2006, 12:28 PM
you gotta tune from the main down. you need to get the main jet to within a couple of sizes of the final required size then go to needle jet then pilot jet
my advice is to hit the dyno to much fucking around otherwise.
and i am not a big fan of spending $60 on 4 main jets just to find out that you need to go the next size up.
ring around and find somone that has a large range of jets that they can keep trying and then you will only pay for the jets that leave in the bike.
02-02-2006, 08:26 PM
As Deano said tune from the main down .... I personally get the main close and then tune from the pilot circuit back up and then do a final main if it needs it ....depends a bit on the bike and what's been done
Try riding in 4th or up ... at about 3/4 plus of max revs ... then roll the throttle back about 1/8 turn ... it should slow slightly ... if it seems to accelerate than it's a sign ya lean...
Best place ta do it is a drag strip ... and check the weather conditions to allow a correction factor and keep going up in sizes untill ya MPH drops and then come back a size and then work out ya correction factor for "worst case scenario" conditions
Changing exhausts can affect low or high rpm depending on the difference in tuned length of the pipes ... but tend to have more effect on the top end and usually require a bit more fuel ..
A freer breathing aircleaner reduces your intake vacuum and usually requires an increase in the pilot curcuit to compensate...
Top end/ main jet is more airflow dependant than vacuum dependant...
The biggest problem with tuning a jap multi is the bloody time it takes to change the jets...
I LOVE fuel injection..... makes tunin so much easier
03-02-2006, 08:55 PM
Thanks boys ill try the bigger mains first and see how i go.
Theres no dynos close to me so its a chor to get to one ill let you know how i go.
08-02-2006, 09:38 PM
Ok boys working it out slowly.
I got it on a guys gas analizer and,
It was running to lean at idle way to rich in the middle of the range
and spot on at the top so,
came out 1/2 turn on pilots and went back up with needle clips by one.
Back to the gas analizer
Now its a little rich at idle but fuck all still rich in the middle
but getting better and still sweet at the top.
So the carbs will come out again and if all is well one more clip up on the
needle should see it just about wright.
Its already running heaps better.
09-02-2006, 01:41 AM
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