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xv920 hitachi -> mikuni carbs

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xv920 hitachi -> mikuni carbs

PostAuthor: Kabutto » Sat Jan 04, 2020 3:36 pm

Hi !
So I'm looking for some advice, perhaps people have already done something this (and i searched the forums, didn't find exact information).

At the moment my 1981 xv920 has the original exhaust system, and original hitachi hsc40 ( i believe) carbs. They are a nightmare. Syncing was very difficult, and even then still not perfect. Both carbs have the mixture screws all the way out (not like they do much in the first place), and the bike stutters at very low RPM.

I was looking into replacing them with something better, and came across these kits
https://www.dimecitycycles.com/mikuni-v ... ml#fitment

I believe they are vm34s? Does anyone have experience with these carbs? Is it possible to sync them (since they are two completely separate carbs) ? They would have 2 chokes, is it possible to convert both to a cable operated choke of the handlebars? Any info is appreciated.
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Re: xv920 hitachi -> mikuni carbs

PostAuthor: nanno » Sat Jan 04, 2020 5:08 pm

Go for twin VM38s and read up on the power-adder section here in the forum. I did a rather extensive writeup on how to set them up and how to jet them.

Also my post where I am showing off my work should have some links to my blog with some step-by-step-guide on how to convert to VM38s or if you prefer TM38 flatslides.

Hope this helps
Greg
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

*Look to my profile for a link to my blog*
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Re: xv920 hitachi -> mikuni carbs

PostAuthor: Kabutto » Sun Jan 05, 2020 3:31 pm

I found the links to your blog's write up about the vm38's, but not the power-adder ? No wonder I can't find much info on the forums, when its hard to even find a specific thing.

Why do you recommend vm38 as opposed to 34s ?

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Re: xv920 hitachi -> mikuni carbs

PostAuthor: nanno » Sun Jan 05, 2020 5:19 pm

VM34s are too small and you restrict your top-end for no gains on the bottom. Strictly speaking VM38s are a bit on the small side as well, but the VM40 was shelved by Mikuni a few years ago. That being said, that's complaining on a very high level.

There's also a post by me on TM38s*, which do work even better on top, but in about a year of testing I haven't found the perfect needle and needle-jet combination to give the same midrange performance as the VM38 roundslides.

*plus again, a rather extensive writeup on my blog on the same matter
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

*Look to my profile for a link to my blog*
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1984 XT500 4Valve (Austrian Tax saving edition)
1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male

Re: xv920 hitachi -> mikuni carbs

PostAuthor: Kabutto » Mon Jan 06, 2020 11:27 am

That is interesting !

I wonder why the specifically made kit includes vm34s and not bigger carbs then.

I read somewhere that a somewhat smaller mechanical carb flows the same as a bigger CV carb.

How's the low down performance of VM38? I ride in the city mostly, so almost never WOT.

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Re: xv920 hitachi -> mikuni carbs

PostAuthor: nanno » Mon Jan 06, 2020 1:05 pm

The VM34 fits with the rear carb-to-frame rubber elbows. I suppose that's why they went with it.

VM38: very, very good down low. You will wonder how they could kill so much power with the CV carbs, after you installed them and dialed them in.
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

*Look to my profile for a link to my blog*
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Bike year & model: 1981 Yamaha TR1
1982 Yamaha TR1 Turbo
1977 XS 750 Sidecar
1984 XT500 4Valve (Austrian Tax saving edition)
1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male



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