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Which Jets?


aguita

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hello...

 

I want to know which jets should i be running with the mods that i have on sig...im looking to remove my airbox and put some pods..im running mostly @sea level or 800ft temp 80-90..my bike is ported by a guy that is very reputable here in my country and have one of the fastest shee around and has built fastest shees here ,He ade me the same port that he did on his bike with the same mods that i have..and he told me that he put some 240 mains on my bike!! i was like WTF 240! and he told me that he made the plug ch

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Well, I don't know much about jetting ported bikes, but if your running stock Mikuni carbs, I can tell you that is way way way way tooooooo low. I run 260s on my stockers with a full air box, FMFs, and no port job. I've heard of guys being up around 400 or so with porting, but I don't know the exact jet size. I can tell you that is too low, but I'm sure someone will chime in with some more help.

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He's got the airbox still on...340s are high unless he has full blown drag porting....

 

People often forget this simple fact about porting.

 

It bascially changes the way your engine pulls air and fuel into it. Often, a ported motor can pull more fuel from a smaller jet than a non-ported motor can. So...there is no rule of thumb that a "ported" motor needs a bigger jet....it's not true.

 

However...TX above did hit the key factor. It depends on port timings.

 

If this guy is a reputable builder, he said the plug chop looks fine...and it runs good to you...ride the bike.

 

"round here....same temps and elevation, with an airbox and no lid, average main jet on a stock port cylinder is 270 to 290...

 

If you're not sure, we can't tell you for sure. You need to learn how to do the plug chop yourself and be sure...

While I'll agree they sound a little small, if you showed me plugs that were colored properly by a plug chop, that'd be enough for me....

 

http://www.dfn.com/benkaren/plugchop.html

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