Hi all been for a blat out today on my mc21, it has the wire splice and airbox mod done, everything else is standard.
goes well starts well so thought i would just give it a quick plug chop just to see how things are
and found the plugs a bit lean, my question is in the summer i seem to remember them being ok
so am i right in thinking that as it's winter the air is denser which leans things off a bit?
so iv'e taped 1 hole up in the airbox and plugs look better, but bike doesn't go as well as i did, would you
leave it with 1 hole taped up for winter then remove tape in summer? or tape 1/2 hole, or remove all tape,
i don't think the it was that lean it was ready to seize,as iv'e been out a few times in this cold weather so would asume
if somthing was going to go wrong it would have already

any help/advice would be great thanks

Yes, cold/damp air will make the mixture leaner.
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Andy.
NSR-WORLD.COM

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Ideally you want to re-jet, and take advantage of the denser air to give you more power!

It is interesting to see that you are effectively thinking about changing the vacuum in the airbox (by adjusting the size of the airbox inlet area) to alter the mixture.
I have to admit that I have never really thought of having a "winter" airbox inlet area and a "summer" airbox inlet area.

Also, in case you don't know already:
The forum rules indicate that you are not supposed to talk about jetting specifics in the free forums.
You have to go to the "paid up" forums to talk about jetting specifics.

So if you do not get very specific answers here, well, now you know why.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

Many moons ago when I used an MC18 almost everyday I did the very same. We found that 4x 25mm holes worked best in the air box lid. However on long trips back in winter late at night I used to tape two holes up. Andy used to take the piss about having a night time setting.

Tank tape used to be able to be reused many times. Myself and Andy often used to stop half way home and pull the tanks off. Those where the days when neither of us used to leave the house without a jet kit.
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If I have to take the carbs off once more...

Those where the days when neither of us used to leave the house without a jet kit.

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"............should have bought a Honda"

My HRC jet kit is never more than 2 foot away from me! I even took it on holiday once!
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Andy.
NSR-WORLD.COM

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thanks for the replys, when i did the wire splice and airbox mod i re jetted so its going realy well
but i was just a bit worried about the colour of the plugs during winter months, so i taped 1 hole up in the airbox
and that sorted the plug colour out but it runs a bit numb now, so i suppose the best thing for me to do is
leave it taped up for the odd day that i do get out because of the weather then remove tape during summer
and do some more plug chop sessions, because even if i get it write now it will change in summer,
ps do you guys do all your jetting while out on the road ? that must take ages having to remove tank, carbs,
rejet then refit everything whats your best times?
no jetting specifics mentioned.

I have a set route I use, about 20 miles round which I know really well so can judge how the bike is running after any changes.

If you note down the summer setting, then go up a jet size or two until your plugs look good, you'll have a winter setting. Two jet changes a year really isn't very much!

Alternatively, you could just fit a detonation counter...

When I read posts like Dave's I wonder whether I should own an NSR.

Why wasn't I born with any mechanical aptitude?

I suppose thats why I have a 28, they don't need looking at as often. I must say my bike goes better on nice cold days.

1 more daft question, so as it is with the wire splice and airbox mod done and the 4 holes in airbox all open and plugs looking a bit lean,will taping up 1 hole in box make it run richer and SHOULD be ok for the winter? or am i waisting my time by doing that, and for best reults re jet??

Thanks

Can't really say if taping one or two holes would be right - only you could answer that, but if you closed offf sufficient holes such that the motor was getting the same amount of air as it was when the air was warmer, you'd be safe.

I'll assume you've heard of stochiometric ratio?
http://en.wikipedia.org/wiki/Air%E2%80%93fuel_ratio

Ultimately, that's what you're trying to achieve...

And Bully, of course you should have an NSR! If you jet on the safe side it'll be absolutely fine whatever the weather, it will simply run a little rich in the summer and not at it's best.

Well, for BEST results, you would keep all the air box vent holes open and rejet. I think everybody would agree with that, yes?
But at the end of the day, without REALLY knowing, I would suspect that the change in mixture due to seasonal or night time temperature is probably fairly minor and in the general scheme of things, not worth rejetting for. Having said that, I definitely re-jet the race bike when going to a track at altitude.

[ as an aside: going to a track at altitude always makes me think twice; at altitude the pressure drops, but almost always, the temperature drops as well. So should you richen it up, or lean it down? This is where the stoichiometric charts come into play I guess. I will leave this as a teaser ]

To know if you should block off one hole or two on the airbox really is a "try it and see" scenario. Where the "see" means looking at the plug after a plug chop.
It's getting down to the nitty gritty here, and it's more about what is practical to do in your mind.

When you are trying to sort the mixture out down to this level of detail, it is best done by fuel injection with feedback into the "computer" on airtemp, pressure, and probably a few other variables thrown in to the mix.

In all practicality,... for road use,... just jet it so that it is ever so slightly rich on a cold winter night (at sea level) and leave at that. Yes?
At the end of the day,.. I think we are best to let common sense prevail here.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

TuckerBag wrote:it's more about what is practical to do in your mind.

That's it in a nutshell really. Is it practical for you to reject a couple of times a year so you know you're getting the best from your engine? Or would you rather be safe no matter what, and just live with the fluffy top end you may or may not notice?
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Fluffy top end it is then, but you know what it's like when youve had a taste of what it Can go like,
it doesn't go bad its just doesnt quite rev as free to 10k and is smoother through the power, i like it when the power comes in it has a kick to it, but as it is with 1 hole taped up it still hits power but more smooth
Thanks for your help fellas