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Carbs and Fuel System
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Thread: Good single carb conversion option? Reply to Thread
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  Topic Review (Newest First)
02-23-2018 06:02 PM
Birga I did some checking on something similar for fuel injecting my 750. The VN 900 uses a twin 34mm throttle body and a split manifold from it to the intake ports, now the 900s ports are nearly directly across from each other. But, if you rotate the manifold up and sideways it should now be facing upward between the cylinders, and have a outlet pointed to each of the 750 ports. A bit of plumbing and you now have an intake manifold with near equal length runners to each head.
I was thinking for a FI setup to put the throttle body at the from of the bike between the ears and duct it back to the intake. The rest of the system could be taken from a Kawa Brute Force 750 FI setup.

However this is about a single carb solution. I haven't checked the spacing, but you might fit a downdraft carb under the tank with an adapter to the VN 900s intake. or turn it and stick a more normal sidedraft carb out somewhere else.
02-23-2018 03:33 PM
DenverDiesel As mentioned before, equalization would be a big hurdle. Since the ports are pointing different directions, one port would have a ~120* bend to meet with the other.
02-23-2018 12:58 PM
Goofyfoot2001 I now own a 1995 1200 sportster and I think the cv carb off that would work PERFECTLY for a vn750. The only real issue is the intake pipe configuration. You figure that out and there isn't much else to it. Mine is mounted on the intake so there isn't even a screw to turn. Throttle should be fine too.

Maybe some custom boots that would fit to these somehow.

02-23-2018 11:45 AM
lugnut1009 Got the factory carbs back on the 99 last night. I'd like to meet the brilliant engineer that designed the carb placement on these bikes, that's ridiculous! And I did it without the air tank thing in the way, it shouldn't be that hard.

It did get me to thinking however, what if instead of a single carb, you used 2 smaller carbs and mounted them on a 90. One on each side, maybe even build a small bracket for each one to help support it. Would just be nice to have something different and at the same time be able to find parts readily available. Just another idea....

** EDIT: I was typing through my thoughts without searching the forum first. Looks like this has been discussed in years past. **
02-21-2018 06:36 PM
lugnut1009 I am just trying to gather info, sounded like a good idea. Not that I will definitely go this route, but never know. Iím not scared to try it though!
02-21-2018 05:11 PM
Spockster The rear cylinder may tend to run hotter.

How about a down-draft carb, might possibly make the manifold simpler, more compact.
02-21-2018 03:50 PM
ubertalldude Yeah, good point, any used carbs would need to be cleaned extensively (ultrasonic or chem-dip) and probably have the float bowl & jet cover o-rings replaced, then reassembled properly. It's not a bad job at all, but those o-rings new cost ~$45 for all 4 of 'em. Ultimately, getting it running correctly would be easiest with the factory carbs I would reckon, but will wind up being a touch more expensive. Getting it running at all with a single-carb conversion will be a TON of experimentation and time invested, but likely not so much on the cost.

Ultimately, it'll be up to the OP which route he takes. If it were me? I'd get one of them running with factory carbs, then try to test out a single carb setup on the second bike. If it took well and was inexpensive, convert the first bike and sell the refurbished carbs!
02-21-2018 03:22 PM
Hexadecimus
Quote:
Originally Posted by lugnut1009 View Post
I did, can't find much useful information. Most threads had ideas or even a picture or two but nothing that said how well it worked or how it did over time... Most of those members have been inactive for years too. Just wanted to know if anybody has seen one that lasted and looked decent. I don't mind fabbing up the intake, and will probably buy one when the time comes and OEM part prices greatly exceed a new Mikuni carb, if not already...
Keep in mind that a used one will need to be fully disassembled to check it, maybe cleaned, maybe new parts, maybe ultrasonic cleaning if it's really bad. A new Mikuni is ready to go, might not even need jets changed if you're lucky. TONS of folks swapping in that carb, so it should be easy to find a 700-800 cc example to start jetting from.
02-21-2018 03:19 PM
ubertalldude saw a youtube video of a guy who said the rear cylinder runs too rich with the single-carb setup he built, and would run OK for a while but eventually foul the plugs really badly. That explains why the slide needles are different from the front and rear carbs...

It seems like there's no one procedure out there, and there will have to be extensive custom fabrication and test fitting, then a lot of re-jetting/resetting the needle height, etc. on the single carb to get it to run right. Unfortunately, doesn't seem like anybody here currently has that setup, and even if they did, we can't even figure out whether or not you should re-jet with an earshave or not, much less figure what jets would go in a single-carb custom setup.

You'll have to go boldly forward with some custom fabrication and carb tuning experimentation, or just buy used carbs off ebay.
02-21-2018 02:16 PM
lugnut1009
Quote:
Originally Posted by Sparkys73150 View Post
Search," VN750 single carb". I think You'll get the info there.
I did, can't find much useful information. Most threads had ideas or even a picture or two but nothing that said how well it worked or how it did over time... Most of those members have been inactive for years too. Just wanted to know if anybody has seen one that lasted and looked decent. I don't mind fabbing up the intake, and will probably buy one when the time comes and OEM part prices greatly exceed a new Mikuni carb, if not already...
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