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Single carb setup tuning

P901 Single carb intake, FLAASH Cams, Super Charger, NOS.......
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Single carb setup tuning

PostAuthor: Basscat » Wed May 20, 2020 1:05 pm

By luck I got a VX700 86 virago with a single carb setup. The last owner toke of the old Hitati's and installed a
manifold with a Mikuni vm30-83 with factory jet setup
Main Jet: 4/042-250
Pilot Jet: VM22/210-40
Needle Jet: P-5 (159)
Throttle Valve: 2.5 (VM34/110)
Main Air Jet: 2.0 (BS30/97)
Needle Valve: 3.3 (VM34/39)
- K&N air intake filter
- Stock exhaust

The last owner didn't have the chance to finish it due to other priorities.

So this is my starting point and want to continue the project.
It was a good running bike, with some carb problems on the back cilinder.
Valves compression are with in specs and I have sparks on the plugs

Question
Before I start with the tuning is the factory jets set good enough to get dailed in or has any one
a other setup as a good starting point?

Btw excuse my English

Regards Bob
Last edited by Jake on Wed May 20, 2020 1:57 pm, edited 1 time in total.
Reason: Moved from XV700 to Single Carb / Power Adder

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Re: Single carb setup tuning

PostAuthor: Flyingdog » Thu May 21, 2020 1:38 am

Personally, I have no experience in single carb conversions..nor would I ever do it. Too me, there's really no gain, except some bottom end grunt. But ya don't stay down there for very long. If our Viragos would be better off with a single, Yamaha would have done it. Gotta remember..that 700 started life with "twin 40mm" carbs. But, I'd never discourage anyone from what they wanted to try. With that being said..mainly wanted to say:
:VTF:

I'm sure someone will jump in and give ya some info for you to work with. Just from what I've read over the years, that size carb is just too small. Even for a 700. Specially if the rear cylinder intake runner is quite abit longer than the front. Best one can hope for is striking that crucial balance (A/F) between the two (cylinders). Specially, since you only have "one" mouth feeding the two. As I'm sure your aware of. Good luck with your endeavor. :cl:
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Re: Single carb setup tuning

PostAuthor: bstig60 » Thu May 21, 2020 4:49 pm

:VTF:


a 30mm carb doesn't do a very good job at replacing two 40mm carbs no matter what your jetting is!
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Re: Single carb setup tuning

PostAuthor: Basscat » Sat May 23, 2020 10:31 am

https://www.youtube.com/watch?v=YflaLENNRaY&t=264s

Is possible conform this canadian guy

:thanks:

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Re: Single carb setup tuning

PostAuthor: mark75 » Sat May 23, 2020 5:36 pm

I started out with a DIY P-901 on my '86-700 with old Hitachi carbs.
the old Hitachi proved problematic.
finally settling with raising the needle with (2) #4 washers {which would be about the equivalent as in the video}

Eventually ended-up with a new KJS system that Ken sent with a new Mikuni that was already pretty-much-all-set-up.
{although expensive, all I had to adjust was the idle}
Ken has since retired and sold the biz - hopefully the new guy is as dedicated and respectable as Ken was.

if I was to do it all over, I would just replace the Hitachis for 2 new Mikunis ...
"Over the Mountains of the Moon,
Down the Valley of the Shadow,
Ride, boldly ride" ... E.A. Poe


Time flies >>> whether you're having fun __ :bike: or not :fan: ---

Any day above ground is a good day.
so Laissez les bon temps roulez. just roll safely --- Semper Vigilans...always watchful

"I hear and I forget, I see and I remember, I do and I understand." ... Confucius*

If you don't read the news you are not informed.
If you read the news you are misinformed.
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Re: Single carb setup tuning

PostAuthor: Basscat » Sun May 24, 2020 7:37 am

mark75 wrote:
if I was to do it all over, I would just replace the Hitachis for 2 new Mikunis ...


Mark can you give the type of the carb for replacement of the two Hitachi's?

Regards Bob

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Re: Single carb setup tuning

PostAuthor: mark75 » Sun May 24, 2020 3:25 pm

something like this >>> http://www.nichecycle.com/ncs/mikuni/ca ... retor.html

tho personally I prefer the round slide ones (just because that's what I'm used to)
>>> https://www.dimecitycycles.com/vintage- ... 1-024.html

however, I have heard of guys putting all kinds of carbs on their mono, even an old VW carb. so it's all in what you think ...
"Over the Mountains of the Moon,
Down the Valley of the Shadow,
Ride, boldly ride" ... E.A. Poe


Time flies >>> whether you're having fun __ :bike: or not :fan: ---

Any day above ground is a good day.
so Laissez les bon temps roulez. just roll safely --- Semper Vigilans...always watchful

"I hear and I forget, I see and I remember, I do and I understand." ... Confucius*

If you don't read the news you are not informed.
If you read the news you are misinformed.
... Mark Twain


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The views, opinions, and experiences expressed in this post are mine and may not necessarily represent views and opinions of other VTF members, so feel free to agree, disagree, or ignore them.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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Re: Single carb setup tuning

PostAuthor: nanno » Tue May 26, 2020 6:12 am

mark75 wrote:something like this >>> http://www.nichecycle.com/ncs/mikuni/ca ... retor.html

tho personally I prefer the round slide ones (just because that's what I'm used to)
>>> https://www.dimecitycycles.com/vintage- ... 1-024.html

however, I have heard of guys putting all kinds of carbs on their mono, even an old VW carb. so it's all in what you think ...


Except for going with something more like 38mm carbs unless you're afraid of your engine actually making power. :cl:
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: Single carb setup tuning

PostAuthor: Basscat » Tue May 26, 2020 3:01 pm

:thanks:

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