I have just purchased a MC18 NSR set up for racing. Was wondering what best set up for filtration for carbs. It came with bare carbs with just an empty air-box sitting on the carbs with no lid on it! I have had to have carbs cleaned and checked by shop as they used to leak fuel everytime I run bike and turned off-leaked out of forward facing cylinder all over bottom of fairing and out onto concrete. Technician found the pilot jets were blocked and float levels in-correct. All back together now and no more leaks and runs better-starts better. I was looking at putting a pair of Uni pod filters on the bike to give it osme protection from sucking in rubbish. Would like to ultimately put these in a closed off air box and feed air from front of bike into air box-to force colder/ more dense air into engine. Someone suggested just have empty airbox (closed off) with a panthose hose stock material over the airbox intake.
What are your thoughts?

franky wrote:I have just purchased a MC18 NSR set up for racing. Was wondering what best set up for filtration for carbs. It came with bare carbs with just an empty air-box sitting on the carbs with no lid on it!

Define "best setup", best setup for what?

The best normal setup for top end power is either an HRC style air tray or just open carbs.

Open air box (i.e. no lid) is a bit of a cheap mans half way house, if you're bothered about keeping stuff out get an air filter (clearly the denser the foam is the more restrictive and the more effective at keeping bits out it will be) and the plate that stops it falling into the carbs (17212-KV3-000) and either a lid with a couple of 2.5cm holes in (the std air box is a restriction) or just use some wire to hold the air filter in place.

It'll make better midrange like that but you'll lose a bit at the top - presuming it's jetted spot on in each case and as it's an '18 that'll be 61-63 bhp which is pretty good.

We saw Andy's '21 pick up a horse just removing his pod filters last year so anything in the way at all is a bad thing when we're talking topend power.

Force feed air has been seen to work well on Bill Limb's '21 as long as the carbs are contained in the airbox, you really shouldn't even run the risk of pressurizing an airbox that does not contain the carbs as well unless you really know what you're doing.
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fontyyy wrote:[you really shouldn't even run the risk of pressurizing an airbox that does not contain the carbs as well unless you really know what you're doing.

I thought all that was required was to run some tubes from the air box to the float overflows therefore maintaining equal pressure either side of the main jet (although I may be wrong )
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If you dont like the way that i ride.....Stop trying to keep up!!!!!

Your right Mick
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If I have to take the carbs off once more...

StephenRC45 wrote:Your right Mick

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If you dont like the way that i ride.....Stop trying to keep up!!!!!

Thanks your advise-would rather gain some usable mid range and loose a tad on top end-only real problem on circuits with long straights and we don't have too many of those.
I have a new problem though-have purchased Uni-Pod filters to put on NSR but because carbs are side by side and restricted amount of room, I can't fit the two filters side by side-attached directly to carbs. Is there some kind of 2 into 1 adaptor you can get so you can fit a single pod filter? Even if had angled necks would be a bit cramped in their with two pod filters anyway- I would have thought-looking at it! Any suggestions?

Just cut part of the rubber mounting on the filter neck so that both filters can fit side by side. Thats what everyone else does and it works alright.
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If I have to take the carbs off once more...

would rather gain some usable mid range and loose a tad on top end-only real problem on circuits with long straights and we don't have too many of those.

??
I would only use midrange for street and on track when selecting a wrong gear, otherwise on track only use top power, never going below 8000rpm
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Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom

So long as you have a decent set of gears, otherwise you end up going below 7 now and again!
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I would only use midrange for street and on track when selecting a wrong gear, otherwise on track only use top power, never going below 8000rpm

You try riding around Llandow without going below 8k
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If I have to take the carbs off once more...

Yep, top end rubbish talk is just that, top end rubbish talk, it's like the reason (normally) 400's kick 250's round the park is not power, it's flexability, everyone who's rode a decent 250 will tell you it should kill a 400 but no one without Dani Pedrosa type skills can exploit that last 5%. Multiple gear changes in corners and dropping out of the power are where time is lost. My 400 makes 80% of it's peak torque (which is more than the average NSR ever makes) at 5000 rpm!

However I'm not talking about just losing power below 8000 by removing the air filter, I picked up 2 bhp at peak but lost everywhere below 10500 rpm, if you keep an NSR reving that high all the time, all power to ya.
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Just get a sheet of Unifilter and put it over the top of your airbox.

http://www.unifilter.com/online%20catalog/accessories.html
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Pressurise the airbox and pressurise the float bowls. Yep, that's a start. The it runs lean at the top because the pressure in the tank is now lower than the float bowl so the fuel won't flow.

Need to pressurize the tank as well to the same as float bowls and airbox.

Then as you're flat in sixth and slam the throttle shut for that first gear U-turn outside the chippy, the high pressure in the tank forces fuel into the float bowl, which is then forced up the pilot and bleeds into the engine in an overly rich condition, so when you rev up out of the U-turn and try to impress the scooter boys all you get is a load of fourstroking and a red face. You then realise that you should have fitted a pressure shut off solenoid between airbox and tank connected to the brake switch.

Ram air eh...piece of cake

Matt@TYGA wrote:Pressurise the airbox and pressurise the float bowls. Yep, that's a start. The it runs lean at the top because the pressure in the tank is now lower than the float bowl so the fuel won't flow.

Surely the 'majority' fuel flow is due to gravity (whilst recognizing that a blocked breather in the tank can reduce and finally stop fuel flow) - Is pressure in the tank really such an issue ?

Ram air is not as easy as it sounds, and yes, for the fuel to flow correctly all the areas have to be pressure equalised.

When I first fitted ram air to the NSR back in the Victorian era we had all sorts of issues. Lots of carb setting, even as far as different float heights, drilling holes in slides etc.

I had two years of messing with ram air on the NSR looking for the best set-up. Then a further couple of years messing with RS125 & 250 ram air in Japan.

You can't just seal up the stock airbox and expect it to work. Engines are complicated and fickle little buggers and they don't like being set up wrong.