OK i now see why we were on totally diff idea’s if it was me forget using the gas tank for charcoal or water , leave the tank for petrol and leave the carbs in place , then go look at Matt Ryders Ammo can gasifier . this would be the best way to go if you want a downdraft and a range and if its short on range just hop off and top up the gasifier in seconds , as Cody says you don’t want to risk yer crown jewels for a few miles of free motoring or anything else come to think of it .
Dave
Do those bikes have an electric starter? I wouldn’t want to have to start up on wood gas with a kick starter. You will also need a battery operated suction blower like Tone uses on his tractor, to get workable gas until the engine can take over. You may be able to get a 140 mile range if you had the gasifier beneath about a six foot tall, one foot diameter hopper strapped to an 60’s style sissy bar. Even that would probably not be enough.
While I did suggest using the fuel tank as a water tank, I know how delicate the one way bearings on these Kawasaki engines can be. I had to replace them twice on my Vulcan 500. Not fun.
Starting on gasoline would be easiest and then switch over to charcoal. Then you could use the engine as a way to prime the gasifier, on an updraft charcoal system this isn’t an issue. I never used a blower for the updraft on my Mazda.
If I crunched some numbers and used propane tank bodies for the gasifier, a reasonably tall system you might get away with 15 gallons or 3 20lb tanks welded together. Or use an old air compressor tank around the same diameter.
Assuming you start to get hot gas after it goes half empty with an average 6lbs per 5 gallons density of fuel(my average), that’s 18lbs of charcoal filled to the brim, 9lbs per refill if it goes half empty.
With my Mazda that would take me 18 miles. Let’s assume you manage double that economy with the Ninja 250, that’s 36 miles of combined economy driving in a town. My Mazda got 2~ miles city driving per pound of charcoal.
With 4x that efficiency you’re looking at 36 miles before needing to put another 7.5 gallons or 9lbs of charcoal back in.
I ran a mixture of wood species in my charcoal, you might be able to get a better density if you only use dense hardwood for the charcoal stock. But then it’s only percentages of gain that I personally consider diminishing returns in the search for wood to burn. If you can source a lot of hardwood then it would be worth it.
To put into perspective how tall 15 gallons at a 12" diameter tank would be you’re looking at something about 3 feet tall minimum. 20lb tanks are 1ft by ft.
The rectangular ammo cans are a good candidate, and you could extend the hopper horizontally so as you lean in the turns it will jostle some fuel into the hopper, but I want to say the most reasonable sized ammo cans I’ve found only hold about 10 gallons, I’d have to measure the ones I’ve bought to figure that out.
A downdraft charcoal gasifier won’t get you better mileage, only the insurance of accidentally adding bad charcoal to the mix and not making tar. They’re heavier on average and the nozzles burn away very quickly if you don’t use a material like silicon carbide. All the space used up for one takes away from hopper capacity as well. With a car or truck it’s worth the weight and size difference but on a motorcycle I personally think an updraft is ideal for the weight. That’s just my opinion though it isn’t backed up with any particular empirical evidence.
Edit: to put things into perspective here’s one of those ammo cans. It’s 32" tall and just barely over 9 gallons in capacity.
I think Koen had different pictures of gasified motorcycles. I don’t know how to find stuff like that.
Giorgio made a post for them.
I’d like to eventually put a gasifier on my Yamaha 1100 V Star. I’d like to get a cargo sidecar though.
Run two of them in tandem to increase range. Hang em on each side like saddle bags.
This is going to be an interesting build. Look at the specs for this engine.
This is not a cruiser. It looks like it only starts producing power well past mid-range and that is one of the biggest bore to stroke ratios I seen. The 11.6 to 1 CR is definitely a plus. I couldn’t find a HP-Torque curve for that engine by it’s way big brother, 4 times bigger, The H2 is available and probably similar.
I really want to see this thing running on WG
I’m currently trying to get a welder so I can start playing around with it. And I’ll try making a stand alone unit for testing on it and other engines out of a old propane tank I have. It’s too old to replace the valve, so it’s a charcoal gasifier or the dumpster 
Make sure to remove the valve and fill it up with water a couple times before you cut or weld on it.
Does your Kawasaki have the double carburetors or a single one?
If your air box doesn’t have any cracks or holes you might be able to adapt it to the chargas, or you’ll have to make your own. You’ll need a valve to reduce the amount of fresh air that goes to the engine.
It has the double, but I’d like to replace it with a simple throttle body setup, and have it so I can just switch from charcoal to gas if I wanted to.
I’ve removed the intake box a few years ago, so it uses double cone filters instead.
If you can find someone that makes an intake manifold to pair into a single carburetor that would make things more simple. I’m sure yours are just clamped into a rubber boot like mine were.
If not you’ll need to make a box with two rubber sleeves to clamp onto the carburetors, with one valve for air and one for woodgas. The air and gas will mix before they enter the carbs. I haven’t seen how well a CV carburetor does with woodgas, I hope they’d work okay.
Edit: I know you already have this bike and we’ll try to help you out to get it running on charcoal, but I’ve been trying to hunt down one of those big single cylinder cruiser bikes to run on woodgas, like a Suzuki S40 Boulevard 650. Or a Harley or other cruiser that already uses one carb.
