1983 XV920 single carb conversion issue (Location in U.S.?)

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1totofanusa
Posts: 4
Joined: Sun Apr 17, 2022 4:28 pm
Location: Sparks Nv
What Virago you Own: 2 1982 XV920's, 1983XV920, 1983 XV920MK, 1982 XJ750 Maxim.

1983 XV920 single carb conversion issue (Location in U.S.?)

Post by 1totofanusa » Wed May 04, 2022 10:51 pm

i have a 83 920 single carb converted, ive got it to run really good but it fouls the rear cyl. plug out within 20-30 miles of city/hwy miles evenly combined, i only run nonethanol fuel and E3 plugs, the front cyl is great. the xv has only 15,000 mi. on it. dont ask me why i chose to do single carb conv, i bought it that way, but i do have PLENTY of 82&83 xv920 spare parts, including 4-5 sets of the hitachi dual carbs.

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jsyzdek
Posts: 241
Joined: Mon Feb 17, 2020 5:31 pm
Location: Oakland CA
What Virago you Own: 1995 XV1100. My dad has a 1996 XV535. I also ride a 2008 SV650S and 2004 Yamaha TTR125. Currently restoring a 50cc Yamaha Champ moped

Re: 1983 XV920 single carb conversion issue

Post by jsyzdek » Wed May 04, 2022 11:18 pm

Regarding the carbs: someone recently posted here about solving the issue by modifying the exhaust. More specifically: making sure that the front and rear cylinder have the same length "pipe". The way the bike is stock, the front has a lot longer exhaust path than the rear. I don't remember the details of how he reworked the exhaust, but it wasn't just the muffler: it was quite a bit more involved.

On another note: I'm a Toto fan, too :)
Keep Calm and Ride On!

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ViragoJoe
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What Virago you Own: 1996 Virago Special XV1100SH

Re: 1983 XV920 single carb conversion issue

Post by ViragoJoe » Thu May 05, 2022 8:46 am

1totofanusa wrote:
Wed May 04, 2022 10:51 pm
i have a 83 920 single carb converted, ive got it to run really good but it fouls the rear cyl. plug out within 20-30 miles of city/hwy miles evenly combined, i only run nonethanol fuel and E3 plugs, the front cyl is great. the xv has only 15,000 mi. on it. dont ask me why i chose to do single carb conv, i bought it that way, but i do have PLENTY of 82&83 xv920 spare parts, including 4-5 sets of the hitachi dual carbs.
===========
toto,

single carb conversion - Why?

viewtopic.php?t=1416

If you have the Hitachi Dual Carbs. Go with them and save yourself a lot of heart burn trying to get the single carb to work properly.

There are to many variables. The type of carburetor being used. Manufacturer of the intake manifold. Slight bends in them make a difference. Not saying that it can't be accomplished. Some have, after a lot of tweaking and $$$ spent. I just don't have the time for it.

You can't correct a carburetor issue by changing the exhaust. You can't correct an exhaust problem by changing carburetion. Yamaha Engineers went with dual carburetion for a reason. If it ain't broken, don't try to improve on it!

Case in point:
When exhaust and/or carburetion are modified there are always consequences :!: Trying to get it to run perfectly as it did when it was new is going to turn into a turkey shoot at best to accomplish. Called hit or miss. Especially, without an expensive dynamometer. Like you will see in the attached video below:

Listen to what he says about Harmonic Reversion.

The problem with drag pipes on a street bike

https://www.youtube.com/watch?v=ezpM5rGpIx8

But again, it is your bike and you can do what you want. I would rather be riding than wrenching on my bike all the time.

Your call on this one.

I'm not a big fan of single carb conversion. Too much work involved to bother with it! And I'm not getting any younger.

If single carburetor conversions were easy you wouldn't be here.

Your Example: fouling Rear Spark Plug in 20-30 miles. Welcome to the world of Single Carb conversions. Isn't it great! Flooding the Rear cylinder with fuel, however, the front cylinder is just hunky dory!

Took a friend of mine 4 years to get it right with his setup.
ViragoJoe 🇺🇸
1996 XV1100SH Virago Special
"Never ride faster than your Guardian Angel can fly!!"
;)


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jsyzdek
Posts: 241
Joined: Mon Feb 17, 2020 5:31 pm
Location: Oakland CA
What Virago you Own: 1995 XV1100. My dad has a 1996 XV535. I also ride a 2008 SV650S and 2004 Yamaha TTR125. Currently restoring a 50cc Yamaha Champ moped

Re: 1983 XV920 single carb conversion issue (Location in U.S.?)

Post by jsyzdek » Thu May 05, 2022 11:37 am

My memory of the post from the gentleman from Florida was fuzzy. You're right: he modified the intake manifold to make it work. I kinda-sorta recall that he did something to the exhaust as well, but I'm not sure. That may have been a separate thing, nothing to do with the carb.
I think he stated then that when the restriction to air flow to both cylinders is the same, then they will work properly with the same mixture, thus making the single carb work via modification of the intake.

I agree: too much work for my liking.
Keep Calm and Ride On!

1totofanusa
Posts: 4
Joined: Sun Apr 17, 2022 4:28 pm
Location: Sparks Nv
What Virago you Own: 2 1982 XV920's, 1983XV920, 1983 XV920MK, 1982 XJ750 Maxim.

Re: 1983 XV920 single carb conversion issue (Location in U.S.?)

Post by 1totofanusa » Thu May 26, 2022 4:49 am

thank you all, going with the orig dual carbs opens synch issue that for ME is a headache at least. I went with a hotter NGK platinum plug in the rear cyl. it improved the miles before total foulout, about doubled it. i guess i can install the Dynojet kit and drop needle half a clip. im afrad if i downsize main jet it will run too lean in the front.

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