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Light throttle return spring mod


jjmaine

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Jun 10, 2023
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Since I fitted my progressive quick turn throttle I've been wondering if the common spring mod done on the mt-07 would work because if you shorten the throw it makes your throttle turn that much harder. Basically, if you cut the throttle throw in half, it effectively doubles the spring rate and I have been noticing it on longer rides.

So I did the only logical thing, made a really low offer on an eBay Fz6r throttle body and bought a light spring from Spears Racing for the Mt-07 to test on it. They were asking $100 for this complete throttle body that came off a good running, low miles Fz6r but the took my offer of $40 so I figured why not. Lots of good parts on it, injectors, fuel rail, injector harness, fuel line etc....

Now to see if the spring works (it looks like it will) and the install on my bike. If it doesn't work, I planned on using the spring off this TB to send to a spring manufacturer to make me some lighter spring rate copies to try.

The crazy part. It cost me $53 to buy this spring from Spears after shipping lol. Tell me that's not ridiculous money for an 8" piece of wire bent in a circle. The things I do for you guys (mostly for myself) in the name of science!
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The Mt-07 spring doesn't work. It's a smaller diameter and clocked the wrong way so you have to "wind" it up too much to get the throttle wheel on and it hits coil bind.

I ended up re-bending the hook on the stock spring so it has less preload when installing the throttle cam. It used to require 180° of preload to fit the cam and now only requires 90°. I measured it vs stock on my "junk" throttle body and it is about 25% lighter.

Install is super easy, there's nothing to it. If anyone wants to modify their stock spring to get a lighter throttle let me know. I can make a more detailed post on what I did.
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Trying to follow your mod. It looks like you bent the hook around about 90 degrees, clockwise from the upper to lower picture. Was that the 'only' thing you ended up modifying? It looks like the bracket where the throttle cables are mounted is in the vice, does that 'remove' from the injector assembly easily, or do you need to pull the entire injector assembly from the bike to do the mod? Interested in a lighter spring rate, but not in pulling the bike half apart to do it. :)) (Old man wrist fatigue is an issue here).
 
Oh no, that throttle body was one I got off eBay so I could do some investigating without messing my bike up lol. On the bike, all the work is getting to the throttle cables and then just undo the 12mm nut and pull the wheel and spring off.

Then re-create the bend 90° back so the wheel has less preload when you re install it. I'll go out in the shop and take a few more photos and try to explain myself better. It's honestly so easy, it's easier to do it rather than explain it lol.
 
Oh no, that throttle body was one I got off eBay so I could do some investigating without messing my bike up lol. On the bike, all the work is getting to the throttle cables and then just undo the 12mm nut and pull the wheel and spring off.

Then re-create the bend 90° back so the wheel has less preload when you re install it. I'll go out in the shop and take a few more photos and try to explain myself better. It's honestly so easy, it's easier to do it rather than explain it lol.
Okay, thanks. I think I understand what you did. :)
 
All you need to do is hold the spring in place so the bottom tang is up against the post on the TB (like it will be when it's installed), mark the bottom of the spring with a sharpie and then bend a hook in that spot for the wheel to catch on (I just used 2 pair of needle nose pliers). Cut off the extra and you're done. Look at my photos above, one with the stock spring in position and the one after I bent a new hook.

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You could also just rotate the spring clockwise 90° so that the straight tang is resting on the lip of the TB. I didn't trust this method but it would achieve the same result.

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Look at this video, it's the same method to remove the spring on our bike.

 
Okay, thanks. I think I understand what you did. :)

Like I said before, I measured the difference in pull weight on the bench and the difference was about 25% but the n the bike it feels drastic and more like 50%. At least in my bike with a quick turn throttle. It should help with the fatigue a lot. Hope you try it and that it works for you!

Another thing to note. Our throttle bodies have a second spring so that even with the main spring removed, the butterflies snap back on their own so this mod is perfectly safe IMO.

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Thanks for the clear explanation, and the helpful video. I may see if I can order an 'extra' spring and give it a shot. If it works out, I will keep the modified version, if not, I can go back to the original spring. :) It looks pretty straight forward to modify the spring, and install it. :)
 
I don't think you can order just the spring but you can do what I do, lowball eBay sellers and see who bites and buy a complete TB for the spring.

I requested some quotes from spring companies to have some 50% lighter springs made as well. If they are cheap enough I'll order a few.

Here you go, offer em $20 and call it a day!😁. If these springs were available from Yamaha it would cost that much for the spring and shipping anyhow.

I have an extra spring but three of the companies I requested quotes from emailed me back saying they need me to mail in my "sample" before they can give me a quote on making some lighter springs. Otherwise I'd bend it same as mine and send it to you.

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Dude what the hell look at the quote! $262 per spring with a 5 week lead time. $457 per spring if I want them in a week! You can keep the 12" of music wire lol😆

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That's odd huh? My bike came with Oxford heated grips and i didn't notice that the throttle was stiffer. But, I did take them off pretty quick after I bought it, I just didn't like how fat the grips are. Like holding on to two Pringle cans lol.

Is yours sons Mt-07 throttle harder to turn with the R6 throttle?

The Fz6 guys (same throttle bodies except from r the bore size) just lift the spring tang over the post with a screwdriver to relieve tension on the spring a little. You could try that instead of modding your spring. Just trying to toss out ideas🤔
 


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