How about a re-jet without other mods...? - Sportbike Forum: Sportbike Motorcycle Forums
 
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post #1 of 5 (permalink) Old 10-04-2001, 01:32 PM Thread Starter
 
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How about a re-jet without other mods...?

Anyone re-jet without a pipe and or freer flowing air filter? Most seem to agree that the bikes come lean to meet epa so I would assume that just jetting it correctly would be beneficial. Part of the reason I ask is when changing plugs yesterday they were white as opposed to tan so I am guessing I am a bit on the lean side. This is with an unknown brand can and stock air filter.
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post #2 of 5 (permalink) Old 10-04-2001, 03:24 PM
 
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i suppose you could, but it wont help that much. your shoveling more gas in but it doesnt have anywhere to go. your stock exhaust is way too restrictive, it cant breathe. do them both at the same time and unleash the monster.
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post #3 of 5 (permalink) Old 10-04-2001, 03:48 PM
 
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Quote:
Originally posted by shannon muse
do them both at the same time and unleash the monster.
Definitely correct here. If you're gonna jet it, you need to be able to supply more air to the combustion chambers in order to compensate for the added fuel (enter: High flow air filter). Also, you need to have a freer flowing exhaust than your stock one. With the added air and fuel you're throwing in the cylinders, the gasses need to be able to exit freely.

As a side note: when you do all this, save the extra $$$ and buy a FULL exhaust system. Up until the '98/'99 class of bikes were released (R1, F4, etc...) the headers were not that great, and you'll notice a definite advantage over stock header pipes.
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post #4 of 5 (permalink) Old 10-04-2001, 07:39 PM
Dad
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Re: How about a re-jet without other mods...?

Quote:
Originally posted by RobG
Anyone re-jet without a pipe and or freer flowing air filter? Most seem to agree that the bikes come lean to meet epa so I would assume that just jetting it correctly would be beneficial. Part of the reason I ask is when changing plugs yesterday they were white as opposed to tan so I am guessing I am a bit on the lean side. This is with an unknown brand can and stock air filter.
Actually, yes you can. As you remarked, from around the mid '80's on, they come from the factory as lean as possible for emmissions. If you note almost all horsepower claims for pipes are the "pipe AND a jet kit". The "and a jet kit" part is probably more than half of the claimed increase. As with any daily driver, pipe or not, you shouldn't go more than a Stage 1. What I have done on my bikes and several friends bikes is just shim the mid-range needles between .015" and .020" which improves throttle response and mid range performance/driveability, which is where you're running 99% of the time anyway. My main incentive for doing this is that over the long haul, it's easier on exhaust valves and I put a lot of miles on my bikes. The improved performance is a welcomed by-product. If you went with a jet kit, you might achieve peak HP increases in the 2 to 5 HP range as well. Hope that helps. BTW, my bikes are bone stock in every other way, including the reflector on the mud flap.

If you would decide to screw with shimming, post again and I'll try to give you some pointers. My experience with this is primarily with Hondas, but the principles will cross apply.

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Last edited by Dad; 10-04-2001 at 07:54 PM.
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post #5 of 5 (permalink) Old 10-06-2001, 07:21 AM Thread Starter
 
Join Date: Jul 2001
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Thanks to all...

I was considering going a full pipe/jetting/filter but with all the costs involved maybe not. But what I would like is the bike to run at its full potential with just the slip on so maybe the shimming would be helpful. I will look into that, thanks Dad.
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