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post #1 of 11 Old 03-11-2012, 04:58 PM Thread Starter
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Carburetor tuning

I have a 1999 zr500 and its runs rich, the carbs are stock how can i make it more snappy?
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post #2 of 11 Old 03-12-2012, 12:58 PM
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You'll have to install smaller main jets. Search for threads on doing baseline jetting set ups. You may have noticed that the sled runs better the colder it is out, so if you tune it to run well in warmer temps, it could be too lean in colder temps and you could melt pistons. This is why it is important to know what jetting you need for the conditions of the day. The carbs use fixed jetting, so you have to compensate for varying conditions by manually changing the jetting.

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post #3 of 11 Old 03-12-2012, 08:10 PM
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Cats are jetted rich from the factory, I had to drop the jets on my 580 quite a bit to get it were it was running well. If you ride in a wide variety of temps and elevations it may be worth it to install a variable jetting system such as vari flow or dial a jet. There are a few on the market.

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post #4 of 11 Old 03-12-2012, 10:24 PM Thread Starter
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Im just a flatlander so elavation isnt a problem it has a 360 main jet now and my book says thats good for -40 to -20, i ride 10- 40 degress so im thinking like a 340 or a 330?
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post #5 of 11 Old 03-13-2012, 07:12 PM
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I dropped my 10 at a time, I ended up going from 350 to 320 but that was on a 580 yours is most likely going to be different. Personally I would go a bit at a time and keep checking your plugs and piston wash, Its a PITA but its better than burning down a piston. Was the main reason I bought an EFI cause I do some flatland sledding but also like to head to mountains once in a while.

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post #6 of 11 Old 03-14-2012, 03:25 PM
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Originally Posted by arcticrider500 View Post
Im just a flatlander so elavation isnt a problem it has a 360 main jet now and my book says thats good for -40 to -20, i ride 10- 40 degress so im thinking like a 340 or a 330?
You book should also tell you the recommendation for 10 - 40F. Each main jet is usually good for a range of about 25F. You would be an ideal candidate for the Holtzman Tempa-Flow. It automatically compensates for changes in temperature and works awesome. The factory jetting chart will also err on the side of being rich at all ranges, so learning how to tune the carbs and find a good baseline is always very important.

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post #7 of 11 Old 03-15-2012, 09:47 AM
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Get the vari-jet setup it saves a lot of time especially when temps change on the ride.
Also add 2-3 oz oil to gas tank when its real cold like -25+ but keep an eye on plug color.
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post #8 of 11 Old 03-15-2012, 11:07 AM Thread Starter
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Will i gain any gas mileage from these jet changes?
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post #9 of 11 Old 03-15-2012, 12:55 PM
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Yes, smaller jets = less gas consumption. It's like drinking a drink with a smaller straw. Takes longer. But keep in mind that the factory jets tend to be set to err on the side of being rich, to avoid a meltdown during the warranty period. The factory spec and even the manual suggestions are just a starting point. Then it's up to you to fine tune. You don't just want to go lean on a hunch or with the hope you'll get more zip. If you're already lean and you do that, you'll find yourself vacuuming your piston out of the lower casing in no time.

If you have EGT sensors, that helps. Should run between 900-1200 degrees farenheit. Colder and you're likely rich, hotter and you're likely lean. Plugs tell you a lot too. But the key is in the piston wash. A properly tuned motor will have burnt carbon on the head of the piston on all but the outer half inch circumference. If it is all black, the piston is getting too hot and you're running lean. If it is clean on more than the outer half inch of the piston, its running too cold and that means you're running too rich. There is a thread on here with photos of each condition (rich/proper/lean). Very helpful. Search "piston wash" or check my posts to find it. Use a bore light in the spark plug hole with the piston at BDC to view the piston crown, or pull the head off. I suggest that you buy a bore light or make one. I bought an incandescent LED at Radio Shack for 79 cents and soldered wires to it with heat shrink for insulation and ran the wires to a battery pack with 2 AA batteries. Sink the light into the spark plug hole and take a peek.
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post #10 of 11 Old 03-18-2012, 01:10 AM
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Will i gain any gas mileage from these jet changes?
When your carbs are well tuned you will get many benefits, the best being that the engine will make it's maximum power and use the least fuel. Don't concern yourself with EGT gauges. EGT gauges are only for monitoring a known condition and should not be used for tuning an otherwise unknown set up. You have to tune your carbs by reading the spark plugs and piston wash and only after you have done that are EGT readings of any real value. Every sled is going to have it's own ideal EGT numbers because the probe placement and gauge are different in every installation. You should not try to tune to a number until you know what that number is for your own particular installation.

Do a baseline jetting set up, calculate the main jets needed for -30C (-25F) and install a Tempa-Flow and then forget about changing jets ever again.

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