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2018 Kawasaki Ninja 400
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Discussion Starter · #1 · (Edited)
Many of you have probably heard of, or even done the Yamaha R6 Throttle Tube Mod for the N400. You can purchase it here with grip pre-installed:

Short Throw Throttle w/ Grip for Yamaha, Kawasaki (OEM R6 Throttle Tube)

Norton Motorsports has a very detailed write-up with photo going over whats required to install this mod. You can read it here:

How to install an R6 throttle tube in the Kawasaki Ninja 400 / Z400

As always, when installing a race or short throw throttle tube, it's always highly recommended to install a soft pull spring at the same time. "The shorter you make the throttle throw, the harder it is to twist the throttle, since the force necessary to twist the throttle increases 1:1 as the distance decreases. So if you cut the throttle throw in half with a race throttle system, the force to pull the throttle is doubled and it starts to be annoyingly difficult to twist the throttle and your grips will start to spin." - Norton Motorsports

You can purchase the soft pull spring here:

Norton Racing Soft Pull Throttle Return Spring – Kawasaki Ninja 400 / Z400

I did the R6 throttle tube the moment I bought the bike before I ever rode my N400, since I had it on my R3 as well. I bought the soft pull spring a short time later though, and jsut got around to finally installing it (I've been riding my R3 more over the last year), and as such ran into common issues that people ask me about all the time, and I took the time to thoroughly go throw and fix them.

Many have ran into issues where even after filing and modifying the OEM housing and adjusting cables as much as possible, the throttle still is crunchy or sticks. The obvious answer is of course, pull it apart and file more until it no longer is crunchy or sticks. The next answer is of course clean and lube your throttle cables. If that still doesn't help, be sure your handlebar is clean, and you can apply a thin (by thin, I mean use a paper towel or shop towel to apply) film of grease on the handlebar under the throttle to ensure the tube itself rotates freely and smoothly.

However, some may still run into issues, and I'm here to address some that I found while installing my soft pull spring.

1. Cable Guide/Tensioner is Contacting the Tube. It's possible that the cable tensioner guide (the farthest forward cable, installed last on reassembly, has the housing side tensioner) may in fact be coming in contact at times with the throttle tube itself. I cut the guide/tensioner shorter (the bit that sits inside the housing) and filed it down to be smooth. I filed mine more so the cut portion was flat after these photos, but for illustration here's the piece I'm talking about.

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2. Throttle Tube Contacting the Sides of the OEM Housing. If you try rotating the throttle inside the housing before reassembly, you may notice the tube contacting the sides of the OEM housing, if this is the case, remove the tube, and either file or sand with a fine tooth or grit the sides of the throttle tube until it no longer contacts the inside of the housing when rotated with cables attached. Be careful, as you don't want to remove too much material, you can also slightly sand or file the sides of the OEM housing to also create clearance. It's important that every surface be smooth though so it isn't crunchy and slides easily. You can again apply a very thin film of grease with a shop towel or even cable lube to assist in smooth operation on these surfaces.

3. When Reassembling Don't Over Tighten the OEM Housing Screws. This may seem simple, but it's something often done. When reassembling, tighten the top screw first using a JIS screwdriver (It's a Japanese Motorcycle, keep rounding out screws on your bike? Get a JIS Screwdriver set. This is the one I've used for years, and have two sets of: Hozan JIS-5 JIS Screwdriver Set (NEW 3rd Gen.) ), then when you tighten the second screw (lower screw) go until the throttle catches when twisted, then back off slowly until it doesn't. If you've already followed the write up, and everything above, it shouldn't need more than a quarter to a half turn out before the throttle returns (provided the cables are tensioned correctly). This will still be more than enough to hold the housing in place firmly, and will prevent any binding on the housing.

4. Cable Routing and Tensioning. This one should have already been addressed long before this point, so if you haven't addressed this, it's on you completely. However, it's the most common issue, so I'm hammering this one till it's dead. Make sure your cables are routed correctly, no kinks or sharp curves, free and clear especially from full handlebar lock both left and right. If you have aftermarket clip-ons like I do, routing may need changed or adjusted. Tensioning will always change with this mod, wether you have OEM or aftermarket handlebars. Think you set tension correctly but still not working? Go to either extreme on both tensioners! This means 4 different configurations (maxed out tension positions). Then find where it needs to sit on both. You always adjust the throttle body side tensioner first, then the housing side tensioner.

5. I've Done Everthing in the Write up, and Above, Still Catches When Reassembled! If you've reached this point and are still having issues, go over and double, or triple check everything again, because chances are you missed something, or didn't tension or route correctly, or didn't file enough. If you've gone through all of this multiple times, then take it to shop and have them do it.


Hope this helps those out there who are having issues with the Yamaha R6 Throttle Tube Mod.
 

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One engine, 2 wheels, reformed squid rider 😂🐙
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So to be a bit more specific on the soft return spring is this also recommended for the R6 mod or no?

I ask because I e done the mod and the spring tension still seems fine and probably not warranting the need for the softer spring.

I would think if an actual race throttle tube, not the R6 tube were to be used then the soft spring would be an ideal accessory for the race tube mod. Yes?

Just trying to clarify this so there's no confusion and excellent post for sure. 🤙
Yup I read the when thing. 🤓
 

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2018 Kawasaki Ninja 400
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Discussion Starter · #4 ·
So to be a bit more specific on the soft return spring is this also recommended for the R6 mod or no?

I ask because I e done the mod and the spring tension still seems fine and probably not warranting the need for the softer spring.

I would think if an actual race throttle tube, not the R6 tube were to be used then the soft spring would be an ideal accessory for the race tube mod. Yes?

Just trying to clarify this so there's no confusion and excellent post for sure. 🤙
Yup I read the when thing. 🤓
It's highly recommended still, and I did it on my R3 and its vastly helped to the point that whenever I rode my N400 my throttle control would always get thrown off since they're geared the same. The main advantage of course though is endurance, as it requires less effort to turn, which was why I did it on my R3 originally. Used to be the 400 was my track bike and the R3 was my street bike. I would go on group rides with the local R3s, and since it was an hour to the ride destination and then ride for hours, then ride back an hour home late at night usually, I'd have a bit of arm pump and my wrist would be sore from just holding the throttle open all day basically (LA area, just lane splitting at top speed basically to get to Malibu and back lol). So I swapped it out to the soft pull spring, and it vastly helped endurance, and I was able to precisely control the throttle on tighter turns at the track and in Malibu. So when the R3 became my track only bike after crashing my first N400, it was ready for the Kart tracks where I practice already, and really helps there.
 

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It's highly recommended still, So I swapped it out to the soft pull spring, and it vastly helped endurance, and I was able to precisely control the throttle on tighter turns at the track and in Malibu.
This is the answer I was looking to hear from you and good explanation on 'precisely controlled'.

Smoothness is key on the track especially the corners and something I'm working on everytime I ride.

I may try this next time I r got the bike torn down and see how this works. 👍
Thanks for the information sir. 🙏🤙
 

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Excellent write up @NinjaBraap, you laid out the proper instructions and problems that may arise. I did the R6 throttle mod in 2019 and love it. I also did it on 2 different N300s that I had. IMO, it’s a must have on these bikes. It’s an excellent bang for your buck!!!
 

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I bought the Spears spring as it was cheaper, had an actual figure of 20% less tension than the OEM which is not mentioned on Norton's site, and I'm not partial to Norton or Spears as they both are quality suppliers of our beloved bikes.

I rock their stickers on my bike as they both are my favorite sellers as is STG. 😁
 

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Great writeup. Mine is OK but I'll see if I can improve it with some of these tips when I go to install the soft pull spring. Currently on its way from STG.

The throw is much better compared to stock, but the soft pull spring is definitely needed.

This is the Motion Pro R6 (2006+) throttle tube (left) VS the stock Ninja 400 (right).

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Just got my spring installed. Huge difference!

Throttle still feels a bit 'woody' and not buttery smooth. Perhaps I need to do some sanding and cut the cable guide/tube.

Edit: Did the sanding - first a rough sand with a medium sanding sponge, then then wet/dry with 1200. A little bit of grease on the cables where they sit in the housing. Cables lubed with Motion Pro lube and luber. Cut the guide with a Stanley knife about 1cm-ish. Stock cable routing. Much better. Not perfect but maybe thats as good as she gets (I probably have unrealistic expectations).

Overall the soft pull spring is 100% worth it! Night and day difference.

Thanks for the tips.
 

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Just got my spring installed. Huge difference!

Throttle still feels a bit 'woody' and not buttery smooth. Perhaps I need to do some sanding and cut the cable guide/tube.

Edit: Did the sanding - first a rough sand with a medium sanding sponge, then then wet/dry with 1200. A little bit of grease on the cables where they sit in the housing. Cables lubed with Motion Pro lube and luber. Cut the guide with a Stanley knife about 1cm-ish. Stock cable routing. Much better. Not perfect but maybe thats as good as she gets (I probably have unrealistic expectations).

Overall the soft pull spring is 100% worth it! Night and day difference.

Thanks for the tips.
Does the throttle snap back freely? It should, if not you have more trimming too do !
 

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You could maybe trim/cut the R6 throttle tube, but nobody in this threat is suggesting it. You can sand the sides if you think its necessary.

As Mr. Brraap said above, you want to cut the cable guide (that's attached to the throttle cable).

The (2006+) R6 throttle tube is bigger than the stock one, so it makes contact with the inside of the stock Ninja throttle housing, as well as the cable guide (in the picture below).



I found it necessary to Dremel out the inside of the throttle housing where the throttle tube's cam hits.

To see it for yourself: Put the back half of the throttle housing on the R6 throttle tube and rotate it as if you were using the throttle, then watch where it makes contact inside the housing - underneath and to the back. Those are the areas you want to make some clearance.

There is a thread with a picture somewhere that I found. I'll see if I can find it again.

I also used some 3M PTFE tape on everything and that took it to the next level. Besides the cable drag it's about as good as it'll ever get.
 

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Discussion Starter · #15 ·
When y'all talk about trimming do you mean trimming all around the perimeter, or just the red area to make it look more like stock, or just the blue to make it more like stock? Thanks View attachment 26935
You can lightly sand or file with a fine grit (800 minimum 2000 max) on the area of the red section, all the way around. The sides of the stops you obviously don't want to touch, and also don't take too much material off any one side. You can also sand the flat surface of the entire face (flat area facing the camera in the photo) to reduce the overall thickness inside the house, which will grant more clearance. However if it works just fine, don't sand anything! Sanding/Filing is basically a last resort. Try lubing everything first, and ensure you have filed the housing bits enough first.
 

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Anyone find an alternative to the $45 soft spring?!! That is pretty outrageous pricing for a friggin spring! What about notching the cam so the OEM is further back and not as tight? Any other hacks? Maybe make one from a kit like this?
Here are 200 springs for $7.99 (4 cents each!), hard for me to swallow $45 for one, over 100X the price!! I realize that $60 for this great upgrade is a good deal BUT, I would not pay $50 for a Q-tip that might fix something either.
 

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Ah the price is a bit steep for a spring but well worth it when installed. 👍

I just got done installing mine and man it's a game changer for smoother throttle pull and may help with better throttle control as well.

I'll be adding to this thread with another how to for the spring mod featuring an alternative way to do this.
Pictures will be detailed and may offer some an easier way.

I'll have it up in a day or two. 🤙
 

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Anyone find an alternative to the $45 soft spring?!! That is pretty outrageous pricing for a friggin spring! What about notching the cam so the OEM is further back and not as tight? Any other hacks? Maybe make one from a kit like this?
Here are 200 springs for $7.99 (4 cents each!), hard for me to swallow $45 for one, over 100X the price!! I realize that $60 for this great upgrade is a good deal BUT, I would not pay $50 for a Q-tip that might fix something either.
A larger diameter grip gives you more leverage over the spring.
I put the Motion Pro tube on my bike with a set of Renthal medium(gray)grips.
My hands were more fatigued at the track than with the stock grips/throttle tube.
I switched to ProGrip 722 foam superbike grips because they were larger in diameter.
It gives more leverage against the spring and makes it easier to be smooth.
The larger diameter is easier on my hands and reduces vibration a lot. I wish the foam were more "tacky".
 
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