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Beef
 Post subject: Main Jet
PostPosted: 22 Jun 2011 18:01 
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Current ride: FUBAR...Enough said!
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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

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restone
 Post subject: Re: Main Jet
PostPosted: 22 Jun 2011 18:52 
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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

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chris(madrid)
 Post subject: Re: Main Jet
PostPosted: 22 Jun 2011 20:30 
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If it's that rich - you may need to lean out the midrange a bit too.

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Adam
 Post subject: Re: Main Jet
PostPosted: 22 Jun 2011 21:33 
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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.

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pash
 Post subject: Re: Main Jet
PostPosted: 22 Jun 2011 21:39 
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I would go little by little, no big jumps.

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Beef
 Post subject: Re: Main Jet
PostPosted: 22 Jun 2011 22:20 
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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.

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Beef
 Post subject: Re: Main Jet
PostPosted: 21 Jul 2011 17:12 
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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 :)

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pash
 Post subject: Re: Main Jet
PostPosted: 21 Jul 2011 17:45 
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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.

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Adam
 Post subject: Re: Main Jet
PostPosted: 21 Jul 2011 20:33 
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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

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Beef
 Post subject: Re: Main Jet
PostPosted: 22 Jul 2011 03:54 
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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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