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XR 600 Jetting

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Hi All

Looking for a little advise, I'm running a stock engine, Twin Air filter (snorkel removed) and a race can, jetting is at main 155 and pilot 68 and air screw at 2 1/2 turns as Scott Summers tips.

I would like to open the top of the air box up to let more air in, most of my riding is between 350 - 600 meters, what would be the correct jetting for the mods and the altitude.

Thanks for any help.

I have posted in intake , but no joy as yet.

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Your pilot is likely too big and the main too small. There is no proven jetting recipe for every parts/altitude/temperature/fuel combination. We can get you close, but getting it perfect will be up to you. I would guesstimate a 62-65 pilot and a 158-162 main being a better it. How is the plug coloring?

Don't hack up your airbox; it's not necessary. The "little" trapezoidal opening in the top already has about the same flow area of an 88mm tube...which is roughly 480% of the carb's flow area. It's not a restriction.

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Hi Head Truma.

Thank you for your advise, plug colours looked good, but I'm changing the plug tomorrow, so will double check.

Thanks again Andrew

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Hi All

On my XR on the main jst is a plastic sort of inverted cup that slips up over the main jet ( don't know what it's called, sort of a baffle ) what does it do and does it need to be in the carb, the reason I'm asking is every time I clean the carb it is laying in the bottom of the float bowl, does the float bowl hold it in place when riding, or is it just floating around in the bowl when I'm riding, doesn't seem to be causing a problem, just want to check.

Thanks Andrew

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It's a slosh baffle, there to prevent air bulbbles from entering the jet.

As far as the correct jet, as said, you can get close using what works for others. You can also learn to do it by feel, or on a dyno with an O2 sensor.

Jets-R-Us has a great section on their website on doing it by feel. On the pilot, go bigger until you can trun the mix screw all the way in and the bike still idles ok, then the jet is too big. It should stumble/stall if you close that screw. Go down one size - your mix screw should need be set 1/2 tp 1 turn out.

The main jet, you basically keep going up sizes and see how it feels under FULL throttle. As the mix gets richer, you will notice the larger jets actually make the bike run worse - this would be due to a rich mixture. When your bike loses top end or skips at full throttle, your jet is too big and you go down a size.

Unless you see the results on a sensor or a DYNO, it takes a bit of trial and error. You'll get extremely fast at changing the jets as well, under 5 minutes by your 3rd time probably.

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@Sage: out of interest, is your bike a Euro model? I've never been sure if there was a slight variation for European emmissions nonsense. My XR600R is a Euro one, and came absolutely stock and had been dealer serviced. It was mega lean on the main jet, a 148 I think. It felt awful to ride. 160 main now, fine / maybe a touch rich.

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Hi Caravan Monster.

Not sure if it's a European model, it came with a 152 main jet.

Starts and goes well, the one thing I was hoping to get a little better was when you really snap the throttle open, sometime gives a little cough, I know they don't come with the most upto date cards, just wondering if getting the jetting sorted out, might sort this?

Nice to see a fellow UK owner out there.

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European XR600 have a large dipping headlight / horn / bulky tail light / proper switchgear as standard (same as US market 650L, I think). I'm afraid the cough, or indeed stall, when you snap the throttle open is normal, they all do it. I only notice it riding on tarmac and can live with it. What sort of riding are you using it for? I use mine for greenlaning, hence am happy with the standard air filter and silencer because low / mid throttle response is most useful. We don't get as much opportunity for wide open throttle off road as some of the US and Aussie guys get on the terrain they can access.

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Hi.

Mine's a European then.

We do, well sort of green laneing, as a friend of mine say, high speed green laning:thumbsup::thumbsup:

The cough isn't a big problem, but a couple of weeks ago we went over some local moorland, still a bit of snow about, I was going quite quickly and came on a ditch fillled with snow, GAS IT was my first thought, just at that moment a cough, cleared it OK, but nearly had to clear my pants as well !!

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