YZ85 reed valves.....are they worth the effort?

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busa1300
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YZ85 reed valves.....are they worth the effort?

#1 Post by busa1300 » Wed Jan 02, 2019 11:38 pm

Original Yamaha YZ85 reed valves.
Are they worth the effort in grinding intake area to make them fit?
Is there a noticeable increase in power anywhere in the powerband?
I am planning on having TSA (if he can build them soon) or Jolly Moto pipes and a Zeel ignition....stock carbs.
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Re: YZ85 reed valves.....are they worth the effort?

#2 Post by tacky1 » Thu Jan 03, 2019 1:35 am

I did the mod on both my bikes, But I'm running PWK28s and BT pipes, heavy porting and Gus heads etc on one and Mikuni 34mm, Toomey pipes, heavy porting and Gus heads on the other, I dont know if they make a difference without all the mods, But more air cant be a bad thing... Just take a look at the size of the reed blocks on an RGV250 or any modern two stroke dirt bike, They are bloody huge compared to our little cages, Im sure they made them bigger for a reason
1985 RZv500
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Jeff B
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Re: YZ85 reed valves.....are they worth the effort?

#3 Post by Jeff B » Thu Jan 03, 2019 3:21 pm

Are they worth the effort in grinding intake area to make them fit?

I'd be surprised if anyone has done this mod with stock carbs. I'm sure it would offer some gains, but the more air you feed the reeds the more gains you'll see from the reeds.

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busa1300
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Re: YZ85 reed valves.....are they worth the effort?

#4 Post by busa1300 » Thu Jan 03, 2019 6:01 pm

Talking about the difference between a RGV reed and a RZV reed....
I guess this is why the RGV VJ21 was the first production bike to make 200HP per liter...with 34 Mikuni's

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And as far as stock carbs go....has anyone bored out the 26 Mikuni's to anything larger?
Would a 28 bore be possible?
Seems an easier route than completely different carbs/cables/airbox....?

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Re: YZ85 reed valves.....are they worth the effort?

#5 Post by BigGuy » Thu Jan 03, 2019 6:33 pm

I looked into boring the stock carbs a while back. It can be done but from what I understand the bore has to be cut in an oval. If you just plow through with a bigger round hole air will get by the slides. Also from what I figured you could basically go up to the equivalent of 27.5 mm.
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Re: YZ85 reed valves.....are they worth the effort?

#6 Post by tacky1 » Fri Jan 04, 2019 12:35 am

Yep, I looked into it years ago, It would have to be oval, Something to do with the slide, Its exactly the width of the carb (26mm) and no room to bore a genuine 28mm...
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Re: YZ85 reed valves.....are they worth the effort?

#7 Post by mgtj59 » Wed Jan 09, 2019 3:32 pm

there is a recommendation of Erlenbach Racing (see http://erlenbachracing.co/reedcages%20mods.htm)

I am doing this upgrade actually with my second bike for the race track. I am curious about the result.

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Re: YZ85 reed valves.....are they worth the effort?

#8 Post by busa1300 » Sat Jan 19, 2019 1:21 pm

I picked up a YZ85 reed just to have a look
Cutting into the ports to make them fit is more invasive than I really want for this bike.
But what are the possibilities of cutting the center divider out of the RZV reed?
And the differences between the steel limiters for the reeds...?
Do fiber reed petals need a different contour to limit movement than the steel reed petals...?
Does the shape effect power delivery in a particular way?

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78 GS1000E
80 KD80
82 Katana
84 RZ350
84 RZV500R
86 GSXR1100
86 1100 sportster
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Re: YZ85 reed valves.....are they worth the effort?

#9 Post by Ron57 » Sun Jan 20, 2019 2:12 am

Hi, I tried these out with YZ85 reed petals the rz500 has a Phase 1tune JL pipes And 28mm carbs, couldn't tell the difference
between these and TSI modified reeds.
Cheers Ron.
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Re: YZ85 reed valves.....are they worth the effort?

#10 Post by Jeff B » Tue Jan 22, 2019 3:12 pm

I'm running TDR fiber reeds in TSI modified cages. This was a popular mod 15 years ago. I believe the reeds I'm using are actually designed and sold for the RD400.

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Re: YZ85 reed valves.....are they worth the effort?

#11 Post by silverstrom » Tue Jan 22, 2019 8:45 pm

Speak directly with Tony Doukas. I sent him my TZR reeds and gages and he was happy to help and discuss things.

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Re: YZ85 reed valves.....are they worth the effort?

#12 Post by ncr160 » Tue Feb 12, 2019 3:44 am

hi that cost a little bit but VForce V3 reed valves are a good solution with just a litlle griding. Is this the best Price/HP result ? Idon't know

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Re: YZ85 reed valves.....are they worth the effort?

#13 Post by busa1300 » Sun Feb 17, 2019 8:28 am

Has anyone here tried these valves, or has thoughts on what may be good or bad with them?
At this point, I am looking for minor improvements over the the original 35 year old reeds.
After I get the engine broke in to some degree and see how well it runs, I may then go to modified cages along with better reeds.
Looking for a simple upgrade, but no experience with this theory.

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78 GS1000E
80 KD80
82 Katana
84 RZ350
84 RZV500R
86 GSXR1100
86 1100 sportster
88 FZR1000
89 RGV250 VJ21 SP
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91 TZR250 3XV2 SP
96 RGV250 VJ23 T SP
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Re: YZ85 reed valves.....are they worth the effort?

#14 Post by JonW » Sun Feb 17, 2019 7:26 pm

Its considered by many that the dual stage reeds never open stage 2. What you feel is ok as the torque of the smaller reed opening as that opens no problem, but then it never realises its full top end potential as the intake is made smaller by the 2nd stage not opening.

Id love to see a back to back test of these against a full single reed petal and Im sure its been done, I do feel it shouldnt work, but one can never be sure without testing of course.
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Re: YZ85 reed valves.....are they worth the effort?

#15 Post by silverstrom » Sun Feb 17, 2019 10:01 pm

I think dual stage should be avoided for the reason Jon gives. It has been tested over the years with more downside than upside. I also I think anything made by Boyesen should be avoided. There are better choices.

And consider this: the reed you need will depend on how you plan to use the engine. There is no one size fits all. Once you know your engine requirements you can choose the correct tension and material. The wrong choice will have consequences. I learned that when mine self destructed after 1 hour of use.

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