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Yoshi RS-2 jetting

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I was reading the installation instructions for the Yoshimura RS-2 exhaust system.

The instructions recommend cutting a large hole in the airbox (3.625” x 4.5”).

This is quite a bit larger than the recommended 3x3 mod.

I'm guessing this is so you don't have to change the stock needle.

*Edit* Yoshi instructions recommend a 145 mj.

Just cut the hole and bolt the exhaust.

 

Who here has cut the larger hole vs the 3x3 hole using the Yoshimura RS-2 exhaust?

What's better?

Edited by Stuwy123

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I was reading the installation instructions for the Yoshimura RS-2 exhaust system.

The instructions recommend cutting a large hole in the airbox (3.625” x 4.5”).

This is quite a bit larger than the recommended 3x3 mod.

I'm guessing this is so you don't have to change the stock jets or needle.

Just cut the hole and bolt the exhaust.

 

Who here has cut the larger hole vs the 3x3 hole using the Yoshimura RS-2 exhaust?

What's better?

I would think either way, you would need to adjust the jetting. I have the 3x3 mod and followed the needles/settings as recommended in the JDJetting instructions and it purrs just fine. I'm not sure making a bigger hole will have any positive impact. There was a just another thread about larger airbox holes this past week...check it out.

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I was reading the installation instructions for the Yoshimura RS-2 exhaust system.

The instructions recommend cutting a large hole in the airbox (3.625” x 4.5”).

This is quite a bit larger than the recommended 3x3 mod.

I'm guessing this is so you don't have to change the stock jets or needle.

Just cut the hole and bolt the exhaust.

 

Who here has cut the larger hole vs the 3x3 hole using the Yoshimura RS-2 exhaust?

What's better?

 

The exhaust makes the jetting leaner, the whole cut in the airbox makes the jetting leaner as well, so doing this would make the jetting VERY lean.

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Do the 3x3 if you want to have accurate jetting recommendations from JD or TT members.  Mine is 11sq.in. and I had to jet it a bit richer than the base-line suggestions.

Edited by billdirt1
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I was reading the installation instructions for the Yoshimura RS-2 exhaust system.

The instructions recommend cutting a large hole in the airbox (3.625” x 4.5”).

This is quite a bit larger than the recommended 3x3 mod.

I'm guessing this is so you don't have to change the stock jets or needle.

Just cut the hole and bolt the exhaust.

 

Who here has cut the larger hole vs the 3x3 hole using the Yoshimura RS-2 exhaust?

What's better?

The bits and pieces that come with the exhaust includes a little plastic washer that you are supposed to place on to the stock needle. From memory, you do need to replace some jets as well (not provided) a 25 PJ and and 145 MJ I think it is. Then you cut the hole in the airbox to the dimensions as you have described.

 

If this was better than a JD jet kit and 3x3 hole, everyone would be doing it. 

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I agree that straying from the standard 3x3 hole will throw off the jetting.

I have a jet kit and have been messing with the jetting on my stock bike for a couple weeks.

I've had the carb off 5 times, got it almost down to an art. Haha.

Trying to get the best settings for my bike and atmospheric conditions.

 

Has anyone gone with the recommended larger hole?

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It's a pointless exercise making the intake larger than 3" x 3" on a stock engine..It just doesn't need any more air for optimum performance..

You can make the air opening any size you want, but you would be on your own with jetting it correctly...

You guessed wrong in your opening post..more air with the stock needle and open pipe will be creating an extreme lean condition...

i don't where Yoshimura are getting there jetting data from ,but they need to take a step back and do some homework..

 

Use the JD jet kit...

160 main jet (open pipe) 155 mj (with quiet insert)

Blue needle clip 4

Stock 22.5 pj with ext. fuel screw/ 25 pj with stock fuel screw

2.75 turns

Edited by Craigo 485sm
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I'm just relaying what the instructions for the yoshimura RS-2.

Read 'em for yourself:

http://www.yoshimura-rd.com/images/2166503.pdf

145 mj and shim the stock needle with a 3.625” x 4.5” hole in the top of the airbox.

 

It must work or they wouldn't tell you to do it.

 

The 145mj is larger than stock and shimming the needle will make it run richer.

The open pipe makes it run leaner and so does the larger airbox opening.

The logic seems sound.

 

I'm at 3300ft ASL, cool temps., I run a 150 mj, blue needle, can't remember the clip position, 22.5 pj and 2.5 turns out~ish.

Stock, 3x3 and bored exhaust tip. Best tune so far. Tried and trued.

 

Madchild is running the larger yoshi recommended size with the same setup.

I'll report back after a couple test rides/drag races.

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My first drz came with a full RS3 installed and bone stock jetting. The bike had noticeably more snap than stock, but it ran really lean. It backfired and surged like crazy. I think Yoshi is simply providing the minimalist and cheapest steps to jet the bike so that it won't be overly lean once the pipe is installed. It is in their interest for the bike to "run better" than stock once installed. I'd still put my money on the JD kit since it includes a custom tapered needle designed around the 3x3.

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I have no idea why everyone thinks making the hole a different size really has much affect at all. My air box, has a much larger than 3x3, and I still found the correct jetting to be way too rich for my bike. Sure the recommended jetting resulted in a bike that ran, but it wasn't ideal. Your engine is only going to draw in the amount of air it needs, making the opening larger isn't going to force more air into your engine.

 

You should be using recommended jetting specs as a starting point, and not just assume they are correct or ideal.

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Your altitude and humidity will have a greater affect on the bike's performance for the same jetting.

The recommended jetting is just a baseline to get everything working to an acceptable level. The fine tuning is up to you.

In theory, the engine will draw as much air as it needs to a point. It reality when you have the airbox door off, the required jetting is way different. Getting consistent air to airbox/engine is key. Hence why everyone says to not drill out the airbox door.

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I'm just relaying what the instructions for the yoshimura RS-2.

Read 'em for yourself:

http://www.yoshimura-rd.com/images/2166503.pdf

145 mj and shim the stock needle with a 3.625” x 4.5” hole in the top of the airbox.

 

It must work or they wouldn't tell you to do it.

 

The 145mj is larger than stock and shimming the needle will make it run richer.

The open pipe makes it run leaner and so does the larger airbox opening.

The logic seems sound.

 

I'm at 3300ft ASL, cool temps., I run a 150 mj, blue needle, can't remember the clip position, 22.5 pj and 2.5 turns out~ish.

Stock, 3x3 and bored exhaust tip. Best tune so far. Tried and trued.

 

Madchild is running the larger yoshi recommended size with the same setup.

I'll report back after a couple test rides/drag races.

 

For your altitude.. the 150 main jet will be good, though I would run with the red needle , clip 4 for mostly above 3,000 ft with the stock exhaust...

that end cap has only minimal effect to improving gas flow...

 

shimming the stock needle doesn't change the fuel curve 

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I'm running the exact Yoshi recommended setup. Hole size, 145 main jet and their shim on the stock needle. My bike runs awesome.

Jeremy also has it jetted this was (except for a 146 main) and his runs great too although I'm not sure on his 3x3 hole size. He dyno'd his bike last Friday too. 34hp at the wheel (on a motor with 40k very very hard kilometres on it)

Edited by madchild
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I'm running the exact Yoshi recommended setup. Hole size, 145 main jet and their shim on the stock needle. My bike runs awesome.

Jeremy also has it jetted this was (except for a 146 main) and his runs great too although I'm not sure on his 3x3 hole size. He dyno'd his bike last Friday too. 34hp at the wheel (on a motor with 40k very very hard kilometres on it)

 

can he post the dyno chart with A/F reading, before and after...?

a dyno reading is only as relevant as the base line run done when it was completely stock or "as received"

 

Edited by Craigo 485sm

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