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Ricardo Silva
Joined: 27 Mar 2012
Posts: 3
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 Posted: Sat May 19, 2012 11:45 am Post subject: Is this normal? |
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Hello,
I'm Ricardo, I have a 2008 Intrepid Silverstone with a Rotax Max.
I use to run my kart at a track near my house here in Portugal.
The track is right in front of the beach.
Las week I was running a 170 jet, it was about 25ºc and beeing in front of the sea altitude is 0.
When using 170 jet the kart didn't rev that much, starting to stutter at about 11000 Rpm.
So, I swapped the jet to a 168 (which, according to the manual is for 35ºc) and the kart started to run fine, doing 13100 Rpm down the straight and no stutter at all.
Shouldn't it run better with the 170 ket?
By the way, the track where I run (I don't race) is Kartódromo do Cabo do Mundo, Portugal.
Cheers! |
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al nunley
Joined: 13 Nov 2006
Posts: 3027
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| Posted: Sat May 19, 2012 12:36 pm Post subject: Re: Is this normal? |
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| Ricardo Silva wrote: | Hello,
Las week I was running a 170 jet, it was about 25ºc and beeing in front of the sea altitude is 0.
When using 170 jet the kart didn't rev that much, starting to stutter at about 11000 Rpm.
So, I swapped the jet to a 168 (which, according to the manual is for 35ºc) and the kart started to run fine, doing 13100 Rpm down the straight and no stutter at all.
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“C” is only half the equation. What was the barometric pressure?
The two, together, constitute the “Air Density”, and that’s what will change your need for jetting. Up or down. Get an air density gauge and watch what it’s doing, the need for jetting changes will become much clearer.
Can you convert 170 to inches for me.
_________________
If the data does not support the theory, get a new theory. (Al Nunley)
All else being equal; Compression is the Holy Grail.
45 years, in and around karting |
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Ricardo Silva
Joined: 27 Mar 2012
Posts: 3
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| Posted: Sun May 20, 2012 7:24 am Post subject: |
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Hi, thank you for the reply.
I thought about the barometric pressure, I have to buy a gauge to see.
But when I have the gauge, how do I know which jet is best?
The manual only refers to temperature and altitude.
170 jet is 1,70mm, so converting through google, it gives me 0,0669 inches. |
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Bailey Murphy
Joined: 29 Sep 2010
Posts: 53
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| Posted: Sun May 20, 2012 8:30 am Post subject: |
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| Also if you are following what the book says it can cause a problem. The jets given in the book is what will keep your motor running for a long time 50+ hours and so on but its not the fastest. To give an example when the book says run a 158 jet im sometimes at 148 or when it said 170 i was at 155. If you want the max performance you run leaner than your book and look at the spark plug to tell when you go to lean. My motor still has 30+ hours and running strong so I have had no issues with it |
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Ricardo Silva
Joined: 27 Mar 2012
Posts: 3
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| Posted: Sun May 20, 2012 12:04 pm Post subject: |
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How do you tell by the spark plug that it is too rich or too lean?
My engine was rebuilt in january (new conrod, the old broke) and has about 6 hours now. |
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Bailey Murphy
Joined: 29 Sep 2010
Posts: 53
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| Posted: Sun May 20, 2012 5:49 pm Post subject: |
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| If you take it off and it has a dark color and wet its rich if its dry and looks burnt its lean you want to have it in the middle |
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John Savage
Joined: 30 Jan 2002
Posts: 1252
Location: United Kingdom (Great Britain), not USA state,
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