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Main Jet
https://ukbeg.com/forum/viewtopic.php?f=8&t=11411		 Page 1 of 1
Author:  Beef [ 22 Jun 2011 18:01 ]
Post subject:  Main Jet
I need to downsize the main jet, Pash deems FUBAR is running 17% richer out here in Canada due to elevation.

I have a 162.5 main jet in currently, do I downsize big to say 152 or small to say 160?

I have no idea how much difference you get from jet to jet.

I don't get much time with my bike, so I am hoping to swap once and be as near as dammit!

ANY advice please
Author:  restone [ 22 Jun 2011 18:52 ]
Post subject:  Re: Main Jet
I'd try 155 do a plug chop then go up to 160 if plug looks a bit pale (lean).
If you've got a mikuni its really easy 17mm spanner whip drain plug off bottom of carb, stick something under to catch the fuel, flat head spanner to change the jet, then reverse, be gentle the jet is soft brass ;) :yup:
I've got both sizes spare if you want em.
Rich
Author:  chris(madrid) [ 22 Jun 2011 20:30 ]
Post subject:  Re: Main Jet
If it's that rich - you may need to lean out the midrange a bit too.
Author:  Adam [ 22 Jun 2011 21:33 ]
Post subject:  Re: Main Jet
chris(madrid) wrote:
If it's that rich - you may need to lean out the midrange a bit too.



Aye, that's where I'd look at too.
Author:  pash [ 22 Jun 2011 21:39 ]
Post subject:  Re: Main Jet
I would go little by little, no big jumps.
Author:  Beef [ 22 Jun 2011 22:20 ]
Post subject:  Re: Main Jet
I dropped the needle 2 rungs and mid range seems good.
Will try 155 and see what it's like.......didn't realise you could get at the main jet through the drain plug-I've been taking the carb off each time :!: :roll: lOl lOl
I have a 155, 157 and 160.
Author:  Beef [ 21 Jul 2011 17:12 ]
Post subject:  Re: Main Jet
OK.....now I have a selection of main jets to try, when I downsize, will that mean I will need to raise the needle again, or should it be ok?

Any advice from anyone who's set up a carb before would be appreciated :)
Author:  pash [ 21 Jul 2011 17:45 ]
Post subject:  Re: Main Jet
The raising and lowering of the needle only affects the mixture where the tapered portion is in the orifice of the emulsion tube. This is at around 1/2 to 3/4 throttle. Main jet controls 3/4 to full throttle... Since the emulsion tube is fed by the main jet, reducing the main jet size will have a small effect on the region influenced by the taper.

In summary, put the needle back to the middle position, get it running right at wide open throttle, then address the needle again.

Surely there are some local Buell riders who can tell you what they are running.
Author:  Adam [ 21 Jul 2011 20:33 ]
Post subject:  Re: Main Jet
pash wrote:
The raising and lowering of the needle only affects the mixture where the tapered portion is in the orifice of the emulsion tube. This is at around 1/2 to 3/4 throttle. Main jet controls 3/4 to full throttle... Since the emulsion tube is fed by the main jet, reducing the main jet size will have a small effect on the region influenced by the taper.

In summary, put the needle back to the middle position, get it running right at wide open throttle, then address the needle again.

Surely there are some local Buell riders who can tell you what they are running.



Yep. On reflection, that seems like very sound advice. I was going at it arse about face lOl
Author:  Beef [ 22 Jul 2011 03:54 ]
Post subject:  Re: Main Jet
pash wrote:
Since the emulsion tube is fed by the main jet, reducing the main jet size will have a small effect on the region influenced by the taper.


Thanks Pash, that was they key bit I was unsure of :yup:
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