Is it worth it convert from 2 carbs to 1?

I think everyone knows that a V-Star 650 is a great bike that's reliable, honest, and a wonderful choice for a first motorcycle. I know my 2004 V-Star 650 Classic has been all those things for me

That said, it's not perfect. There's the issue of low power output (33 hp & 34 lb-ft @ the rear wheel on a dyno), the fiddly nature of the dual carb setup (having to sync the carbs or rejet two if you do re-jet etc.), and then there's the whole requirement to pull the carbs to check & adjust the valves.

I found a place that does a single carb conversion kit - KJS Motorcycle Works. It looks like it would cost me about $700 with accessory parts and shipping. They supply the intake manifold, carb, etc. and you install it. I don't think I'd have much if any problem doing the work myself. It looks like it makes a bit more horsepower, a bit more torque, and would be a hell of a lot simpler to deal with I can tell from some of the pics that the carb wouldn't have to be removed to deal with the valves

Here's a few pics from their website:


System installed on a V-Star 650


Another view of an installed unit


V-Star 650 parts left over after installing the single carb conversion

I have to be very careful with what little money I have and I'd probably have to save up for a year or so to do this. I'm already thinking about selling all those leftover parts to recoup some of the cost. I just don't have enough experience with motorcycles and modifications to determine whether or not this is worth the time, cost, and effort. I figure the inmates around here probably have more of a clue than I do

So, what does everyone think about this?

Thanks in advance

How much is "a bit more horsepower and torque"? The reason I ask is that you may be able to get a better bang for your buck by doing a couple of other things.

But first, I am curious as to what you actually hope to achieve by doing this mod, is it ease of maintenance, gains in power (how much do you really think this will net?)

1. If you are overweight at all, losing 20 - 30 lbs would be like getting an increase in HP and Torque, with the added benefit of being more healthy. If you are in great shape, ignore that suggestion.

2. There are ways to lighten the bike up to achieve the same as number 1 if you are already a lean, mean riding machine.

3. A lot of the increases in power certain manufacturers claim just never end up materializing, so I would try to talk to some people that have done the mod. What does this do to fuel consumption? Does performance increase at the sacrifice of economy? If this is the case and you need to watch your $$$ closely, then this might not be the right mod.

4. Jetting the bike properly and getting the correct A/F could be much less expensive than trying to redo the design of the carb setup, and get some decent results. Again, you are in danger of sacrificing economy for performance.

5. I am not sure how much money you will recoup form the takeoff parts. I would see what the salvage shops that list their items on ebay get before you are surprised by what the market might bring for the takeoffs.

I like working on my bike, I have done some things that have made it better, and also spent money that I probably could have saved or spent on something that would have yielded a better result, so my advice would be to just make sure you ask enough of the right questions before spending your hard earned $$$ on a mod that may not live up to your expectations.

I learned a few lessons the hard way (and sometimes expensive way), so hopefully you can avoid that. Good luck!!

Thanks for the reply! I'm looking to simplify maintenance and future mods such as changes in jetting. Jetting can be changed on the stock 20mm Mikunis while installed, but it's a royal pain and you have to do it all twice since there's two of 'em. Getting to the valves for check/adjust now requires removing the seat, speedometer, gas tank, intake manifold, and carbs. It's a royal pain and if I don't have the time, energy, space, etc, it's about 4.5 hours of shop time. At today's shop rates, that's between $350 to $500 in labor alone

I've also meant to open up the intake and exhaust, but I haven't wanted to deal with the jetting changes on the current carbs. It would be pretty easy to get it all corrected with this mod as well. If it gives me a few extra HP & lb-ft of torque, so much the better! Gaining 3 HP or 3 lb-ft of torque would be about a 9% gain

I love the idea. But not at that price. I was going to convert my former four cylinder Goldwing to a single carb, from four separate carbs. If any engine was ever designed perfectly for a single carb, it's the Goldwing four. A guy on one of the GW forums was making and selling the manifolds, and had everything worked out. His ran great in the video. But by the time you added up all the parts, including an automotive Weber carb, it was going to be over $1000. The bike was running ok, so I left it alone. Sometimes I wish I had went ahead and done it. A chance to perfect something that Honda got so close.

Motorcycle manufacturers need to learn a lot about simplicity. The pre '99 Honda VLX600 Shadow had 2 carbs. The '99 and later had just one. They ran exactly the same, except when the 2 carbs on the earlier model messed up. My former Rebel 250 was a twin with a single carb, and ran fine. The Japanese seem to seriously over complicate things just because they enjoy it.

I had a 650 and don't recall having to take the carbs off to do the valves .I did rejet and do a air box mod. All in all I think while it was a pain in the butt at some stages it never justified a radical "fix". Enjoy the time with your bike and take your time, a annual maintenance shouldn't take more then a half a day. Sometimes I miss that bike for light weight and easy handling.

If you're planning on keeping the bike, do it.

I admit I don't know much about the metric cruisers. That single carb setup looks like the HDs I'm more familiar with and makes me wonder V-star didn't put a single on in the first place.

Regardless a 3hp/tq increase likely would be felt seat of the pants.

Once properly jetted how often do you to make changes and what is the valve adjustment interval....how many times/year do need to adjust them.

Of course I'm biased but gotta love the simplicity of the HD cruisers....no valve adjustments ever and can pull the bowl and top off carb to change jets or needle valve without even removing the carb from the bike.


If it was mine, I'd leave it as it because sooner rather than later I'd sell it and a mod like that will likely reduce resale value unless you reinstall stock carbs and can't do if you sell the take off parts.

Also looks like the carb hangs off the side pretty far, how much farther does it stick
out once you install the air filter, will it affect right legroom/clearance.

JerryH - Yeah, I can agree with the need for simplicity. My V-Star not only has a pair of carburetors, but it also has four electric carb heaters that use too much electricity when the outside air temp is below 50 degrees The easy riding does help to make up for that though!

natez1 - It does have easy handling and many other good qualities That said, everything I've seen says you have to remove the carbs. Click here for a pretty good walk through on the procedure. I'd like to have the time to spend a half a day or more working on a vehicle, but I just don't with my job and daughter. I barely have time to ride as it is.

Thanks for that straight forward answer

You know, those are good questions! I don't know how often I'd rejet, but I'm quite a tinkerer at times. I might want to try swapping out the exhaust for example. The recommended valve check interval is 4,000 miles. I let it go 9,000 because of the cost and it was OK, but I'd rather check when I should.in case you missed it, here's a link to the procedure for a valve check & adjustment: is here.

That's also a good question about the distance the carb sticks out. I'll have to think about that...

Thanks again, everyone - I really do appreciate it! One other question to include - Can anyone think of any benefits to going single carb aside from simplicity? Can anyone explain the advantage of staying dual carb?

Have a great night, everyone!!!

My 2006 Honda VT750DC Shadow Spirit has the stock dual carb set-up ... in 2007 Honda offered both the VT750DC AND the new VT750C2 Spirit ... the C2 came with a single carb, same motor, different frame and slightly different styling to the previous version of the 750 Spirit ... in 2010, the C2 Spirit went EFI ...

Can't speak to the advantages/dis-advantages of the single carb vs dual carb other than single carb is obviously simplifies any req'd maintenance ... in the case of the DC Spirit and the C2 Spirit; don't know for sure, but I'd say a near-direct swap of the C2's single carb to the DC is possible ...

BTW, the 750 Shadow Spirit is running approx. 43-45HP for roughly same weight as the V-Star 650 ... sell the Star and buy a Shadow!

Thanks for the reply! I'm tempted to sell the V-Star for something with hydraulic valves & EFI, but I can't do a straight across trade & it will take quite some time to save up the difference.

Is that 43-45 HP for the shadow at the crank or the rear wheel? I ask because my HP & torque figures were at the rear wheel courtesy of Dynojet:



Looks like the Shadow is better no matter what

There are too many other bikes out there to try to build this into what you really want IMO. Drop that $, that you will never get back, for those gains? No way. I bet you could get the same results by deleting the airbox and all its hardware/supporting BS, put a set of K&Ns on it and spend a day jetting it. Under $100.

As far as I'm concerned, I am not a motorcycle engineer or designer, my bike was likely built by someone vastly more qualified than me. There are far more factors to consider than just if it will make more power. Most of the stuff that we get, when in it's in development likely made way more power than the production version of bikes we get. They will de-tune somewhat for reliability and ride ability.
Rideability and things like throttle response are far more important than overall power, I think.
But if it's one of those projects just to see if you can do it and to see what might happen, than have at it.

If it's your first bike, then you're going to eventually want to try something else. So I woudln't dump money into it.

I think you should test ride a Bolt.

I'd save up all the money you can this year , enjoy and ride your bike. Then clean it up, sell it and buy a sportster that already has a carb and never needs the valves adjusted.

Having been involved in automotive development for many years and briefly involved on the motorcycle side, I can say I've never seen a project that had way more power in development than it will have in production. I've seen a few the other way around though.

If a bike comes with two carbs, someone will want to convert it to one. If it comes with one, someone will want to convert it to two. It's up to you if it's worth it. Worth it to me? No. How much time do you spend rejetting carbs and adjusting valves anyway?

Unless you're really good at tuning bikes, have the equipment and lots of time, I wouldn't mess with it. It's way too much money to sink into that bike - you'll never get your money out of it. It will actually decrease the value of the bike because it's not stock. I would sell the bike, take that money plus the money for the kit and get something that's set up the way you really want.

I would even accept some loss of performance on a cruiser for the simplicity of a single carb. You think adjusting the valves on a V-Star 650 is bad, it can't be any worse than doing it on a Ninja 250 or Ninja 500. You have to practically disassemble the entire bike to get the cam cover off. And despite these being twins, they still have 8 valves, and a couple of them are almost impossible to get to because the frame is in the way. A 16 valve sport bike is far worse, and some, like the Honda VFR VTEC setup are such a nightmare they take 6 hours for a dealer to do. That's almost $700 in labor, shop supplies, and taxes to have the valves done. On the Yamaha Majesty scooter, the entire engine and drivetrain have to come out, and to get that out, all the bodywork must be removed.


One of my most important criteria for buying a bike is the maintenance. It takes about 3 hours to do the valves on a Honda PCX150, and it is supposed to be done every 2500 miles. Before actually buying a bike, I make sure tha maintenance is withing reason. If not, I don't buy it, no matter how much I might want it.

I'm interested in converting my GL1000 4 carbs into 1:



Not a bad deal if you don't have to sync the 4 carbs anymore.

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I'm surprised you are not riding an airhead BMW then. Don't know if maintenance can get any simpler than that

That's one thing great about the Nighthawk and other bikes with hydraulic lifters - no valve adjustments. I've been tempted to buy a VFR numerous times but then think about the maintenance and back off. Even though the Nighthawk has four carbs, checking the sync once every 8k miles is no big deal once you've done it.