XJ500T Jaybuilt Kawasaki 500 Bellytank Triple

Jaybuilt XJ500T Kawasaki Bellytank Triple

Jaybuilt XJ500T Kawasaki Bellytank Triple

Builders of incredible homebuilt machines keep popping up and here's another example of a very impressive motorcycle designed for the purpose of handling the twisty roads of California's canyons. This bike consists of a Kawasaki 500cc 2 stroke triple engine, front and rear suspension from a ZX9 and everything else "Jaybuilt." Total weight is 310 pounds!

Jaybuilt XJ500T Kawasaki Bellytank Triple

Jaybuilt XJ500T Kawasaki Bellytank Triple

The whole project was really well thought out. His intention was a minimal part count and easy maintenance, engine swaps are under 30 minutes. He built an engine stand that holds the engine with 1 bolt and slides under the bike. Remove a few bolts, disconnect a few wires and hoses and slide bike away, the engine is on the stand. The entire bike can be disassembled with about 20 bolts in under an hour.

Jaybuilt XJ500T Kawasaki Bellytank Triple

Jaybuilt XJ500T Kawasaki Bellytank Triple

The fuel is carried in the foam filled bellytank, the area over the engine encloses the expansion chambers. He says heatwrap and directed airflow keeps everything cool.

Jaybuilt XJ500T expansion chamber routing

Jaybuilt XJ500T expansion chamber routing

Performance, as you might expect, gets your attention. He geared the bike for a top speed of only 120, he figures he wouldn't be riding anywhere at 160 so why not keep the power where you can use it.

Jaybuilt XJ500T Kawasaki Bellytank Triple

Jaybuilt XJ500T Kawasaki Bellytank Triple

There's a lot of interest in 2 strokes among builders of back road specials. I can only imagine what this bike is like to ride, lots of grins for sure. The readers over at the Bay Area Riders Forum, where the builder talks about it, all seem to like it, a lot, and I have to agree with them, this is one superb build.

Big tip of the hat to Andy, who pointed this out. Thanks!

Link: Bay Area Riders Forum

Jaybuilt XJ500T Kawasaki Bellytank Triple

Jaybuilt XJ500T Kawasaki Bellytank Triple


  1. Walt says

    Lovely to look at and nicely crafted, but I don’t understand the logic of flipping fuel and exhaust position from what’s “normal.” The builder has the hot stuff where it impedes flow to the cylinders and heads and pretty much ensures he’ll get baked at every stop. The fuel, down where road debris and obstructions could damage the tank, must be pumped up to the carbs. But again, it’s a great looking special.

  2. jr says

    Heat isn’t an issue if you’re always flying!

    I love the exhaust routing, a bit crazy, but still awesome!

    I can say I would be a bit nervous having my gas tank nearly kissing the ground, but overall I think this bike is beautiful. Loving all the custom builds kneeslider :)

  3. Viv Collins says

    Very nice build and shows some radical problem solving skills, love the idea of using that motor in a modern frame, the next step might be to reverse the cylinders and route the chambers straight out the back

  4. Spartandude says

    The purpose of the tank on the bottom is weight distribution. By having the center of gravity so low this should be rather flickable. I do agree with the danger to the tank from FOD, but the exhaust heat would not be much of a problem with thought taken for insulation and routing. I like the idea.

  5. JB says

    There are many different and unique design features on this bike! I think the best is that of the quick removable motor. Have a little too much fun and cause some engine damage, just bolt it down and remove it to do the work and the engine stand you already own. Great concept for the tinkerers who are always looking for some more power between dyno runs or races.

  6. nobody says

    Considering where radiators, oil sumps, etc are positioned, I find it hard to believe there is any real danger with placing the tank below the engine.

    I find it both funny and absurd that having several gallons of gas between your legs is somehow desirable or safe. Yet nobody FUDs that design convention.

    Is this a street bike or track weapon? No matter – I love seeing work like this.

  7. Nicolas says

    That’s a nice piece of great mechanic …. I really like the idea of the old school 2 stroke powerplant fitted with modern suspension and an effort to reduce the weight.

    The esthetics is discutable, but that would be a blast to ride … damn !

    Great job

  8. says

    @Viv Collins…

    routing the chambers directly out the back probably would not provide enough exhaust chamber space without changing the look and changing the weight centralization.

  9. RaisingKane says

    Now that’s really cool! I love the Kawasaki triples. I’d like to see one with an old KZ motor, reversing the head so the carbs are in front and the exhaust goes out the back. The belly tank should improve the center of gravity for better handling. My complements to the builder for a great design. Keep up the great work.

  10. Emmet says

    Sweet design, I like how there are blatant criticisms to the placement of that exhaust as to the daily performance of the machine. Gotta understand it’s performance built and moving crazy fast will maintain heat and he only geared it for a top speed of 120, talk about form and function.

  11. Walt says

    It does look like the builder (artist?) reinforced the belly tank with an additional plate at the front and bottom. I would like to see how the weight of the fuel and tank compares with the weight of the exhaust system. In any case, my applause for great creativity and build skills. The original triples were infamous for dicey handling. This should be far better.

  12. nobody says


    If I remember right, a number of TZ700/750s were built (by the tuners?) with the middle 2 cylinder exhaust ports directed aft.

  13. Brian says

    I let me state up front that I think the bike beautuful, but if I’m remembering correctly, when Honda set up Freddy Spencer GP500 racer like this homebuilt, they had real problems. Maybe because of the volume of gas that they were trying to carry, but as the bike went into the corner, the fuel would be swinging out. It made the bike very unstable. They also had heat issues with the exhaust system. I think it only lasted 2 races, before they switched the bike back to the normal setup. he may not be running the engine anywhere as lean as the race bike would have run, and hense, not have the heat issue. Regardless, when most of the US just watch’s TV all day, it’s really neat to see someone push the envelope, nice work.

  14. PUSkunk says

    Lowering the center of gravity is not always desirable. When a motorcycle leans into a turn, it rotates around its’ center of mass. The center of mass of the entire bike, including the rider. This is why mass centralization is such a hot term these days. But with such a light bike and being so short top to bottom, I don’t think the builder will have any problems with flickability.

  15. PUSkunk says

    Anyone else notice the switch to single front disk in the final form? I wonder if the dual disks had too much braking for such a light bike.

  16. terry says

    I like what he is doing and am glad to see something truly custom in mail order custom world

  17. netjustin says

    What an incredible project. I’ve had enough fuss just making a belly pan and number plate brackets.

    Great job on the design too; is there an opportunity to sell a kit here, sans motor?

  18. Azzy says

    Interesting design. I bet the road in CA are a lot nicer, I would rip my tank off in 10 minutes with how crappy PA roads are.

  19. FREEMAN says

    I really like the whole design concept of this bike. Minimal part count, accessibility, mechanic friendly, and fast. I’m not sure I believe it’s just 20 bolts holding that whole thing together but I’m sure it’s not much more than that. I think it would be interesting to leave the expansion chambers and frame exposed, but the heat would probably be quite uncomfortable for the rider. Very creative and excellent end product. Very nice.

  20. Den says

    My dad had a five hundred triple, he called it the widow maker, the engine ended up in a rickman frame. I used to like two stroke in my go fast days but have been a bit turned off lately when I heard how much air pollution they put out.

    Great bike, really well thought out,it sounds like it is supposed to go on the road, will licensing be an issue in CA (pollution)?

  21. says

    @ Nobody

    I never said it wasn’t done or couldn’t be done. I mentioned that, if it was done, it would change the look and possibly centralization of weight.

  22. nobody says


    Understood. Someone explaned the reasons for the TZ cylinder re-orientation – it made sense and I’ve since forgotten what they were.

    This all makes me wonder what his H2 project (if I read the forum link right) will look like…….

  23. P. T. Anderson says

    I like the way this chassis layout allows for experimentation. If I squint just right, I can imagine the tank and pipes in their conventional locations with or without the cylinders reversed. There’s room in there to try stuff out without altering the frame. I could comment more but it would sound like I’m being a downer when I didn’t mean to be so I’ll just leave it with a very earnest – Looks like it will be a lot of fun!

  24. says

    if I see this motorcycle I’m remember my cycle kawasaki GTO110cc very small i like your cycle but i see your body cycle very inflexible in some point.

  25. JC says

    Anyone that criticizes the looks should take a second look at the rear view, those three pipes sticking out look awesome to me, and subtly scream how different this bike is.

    Sure there are other triples, but they are a rarity on the road.

    The workmanship looks top notch to boot.

  26. jay abington says

    hi there boys it looks like most of you like it.I apreicate all the opinion’s and thank you guy’s for taking your time to reply .


  27. Ted says

    The bike looks GREAT and the design features make it quite unique but in looking at it it’s the exhaust system that stands out as a true engineering feat, getting it where it is is one thing but makeing it work is quite another, 2 strokes are VERY touchy when it come to there exhaust design, everything has to be just right or at least Damm close or they will have flat spots on the low end and just plain won’t run good at the top end, my hat is off to this guy.

  28. B*A*M*F says

    I love this bike. It’s super light and likely extremely powerful. Despite what some have said about the high exhaust, the overall layout of the bike seems pretty elegant to me.

  29. jr says

    So what is stopping major manufacturers from building really elegant, simple framed bikes like this?

    I want this bike with a huge single cylinder 4 stroke!

  30. TKG says

    Yeah Honda did this with the NS500…fuel underneath exhaust chambers up top. Cool bike. Not too crazy about the white colored parts.

  31. Tim says

    one thing that interests me is that its referred to as a “back roads special” implying use on the street, but it has zero concession to making it road legal that I can see: no lights, no indicators, no licence plate etc etc. The extra frisson of adrenaline when seeing a cop must make an already exciting ride even more exciting…

    I remember reading a tech article about Spencer’s NS500 with this arrangement. The term used was “polar moment of inertia” IIRC: basically as the tank empties, it drains away from the center of mass. Although the total mass gets smaller (as the fuel is used) it acts further away from the centre of mass which caused slow turn in, and understeer. Hopefully I am not greivously misremembering Kevin Cameron.

    I guess the only way to test it would be to ride it, which I would LOVE to do…….

    makes my own projects seem kind of lame, seeing this stuff.

  32. jay abington says

    Hi all !! the lights are the one thing that i cant make myself …….yet ! and they can make or brake the looks of it so i am foolin with some military stuff at this time nothing I am OK with yet. but it will happen . i am trying to build a hud system for the helmet with rpm ,mph,high beam ,blinker,and kill switch when unplugged .just walk up and plug in and go ! thanks jaybuilt

  33. says

    Great looking bike! As for the gas tank, I wouldn’t fancy my chances riding it in the pot-hole center of the universe where I live. Crack it on the side of a pot-hole and… I wish they’d fix the goddam roads!

  34. JC says

    jr, nobody,

    I’m in the planning stages of an air cooled 650 based cruiser, no reason the same inexpensive motor couldn’t be used on a sport bike chassis.

    Their are plenty of Honda and Suzuki motors like this out there.

    I have no intent of making it a business, I just want ONE.

  35. taxman says

    very good looking bike. i can’t wait to see it with lights and such. the roads in my area aren’t to terrible so the belly tank doesn’t concern me to much. although i would be worried about my twins with those pipes running right underneath them. that must get HOT!

  36. Spartandude says

    @jay abington:
    With the lower center of gravity it should be easy to change orientation, but what about lean angles? In order to sustain momentum through a corner do you have to use more body position change than a typical sport bike with a higher center of gavity? I may be incorrect in my thought processes on moment arms and rotations so I hope you can enlighten me.

  37. Kirk says

    43 comments so far ..that’s what its all about. Jay builds things like this because he can its a passion (the artist thing) I’m sure he has enjoyed every moment of construction and constantly thinks of changes or “next time I’m gunna “

  38. Michael Lackey (aka BykDr) says

    The design that he used seems sensible, I built a H-1 drag bike back in the eighties and one of the main issues was instability caused by engine vibration…his designs has the forward engine mounts come directly off the head. That should minimize that issue.
    I see a lot of talk about his fuel tank location he might have improved it by designing a tank that was below the seat and right behind the carbs…thus allowing the greater mass of the engine to be mounted lower…and possibly building a airbox as a part of the tank design.
    An airbox would allow a large dead airspace which tends to give a bit better low end response.
    As to having the expansion chambers routed upward…two stroke engines are not real fuel efficient and the exhaust tends to rund fairly cool as compared to a four stroke. I have ridden many off road two stroke bikes with up exhausts with no issues. His design really approaches the old Tz 750 design.

  39. Gary says

    Does anyone see a possible wheel jamming between the pipes on fork compression like I do ? YIKES !

  40. Sean says

    Jay, Pariah here from customfighters. Nice to see you getting the exposure the bike deserves.

  41. jay says

    thanks SEAN nice thing to say and all of you customfighters are a class act.

  42. Adam Kitchen says

    Absolutely stunning use of one of the more interesting engines. It makes me happy that people are building such creative, inspiring, and FAST machines! I want to hear this thing hook up in a corner and wind out the line.

  43. jay abington says

    thanks Adam we will have to get togather and you can ride it better yet .

  44. harley manning says

    i would move the gas tank to the rear fairings and have it blend in as if it was part of the plastics other than that thats a hot bike!

  45. GUs THe BUs says

    The Reason for the exhaust is that it is 2 stroke meaning it takes 2 strokes to make one power stroke un like most things which are 4 stroke the exhaust buldges are the expansion chambers When the exhaust comes through the small part of the begining tube it then goes into al larger tube and is then slowed down by the shrinking tube at the end of the expansion chamber and when the stroke starts over and intake starts it sucks back all of the hot oil and gas that has not been burnt or exhausted through the end of the tube already and because the gas is already warm it combusts at a higher rate creating more horse power :)

  46. Scott says

    Watch out, one of the big 3 will probably copy your ideas like they did with someones single rear shock idea 20 years ago.
    If Kawasaki would have built this bike in 69, a lot of bikers would have been able to keep thier 500 on the road.

  47. jay abington says

    thanks for the warning scott but it has ben done by honda back in the 80`s and did not do well . I shure like it and I am going to do a 750 when i ring this one out and find all that needs changing.thanks a gain. jaybuilt

  48. Steve says

    What a fantanstic way to try and tame the “Green meanie” the uk law was changed because these beasts were known to be killers. In the 70’s they had the power but handled like a trash can. My friend had one and it would a regular thing to see him wrestle the bike round a bend. they were evil. A beautiful concept and a fantastic way to recycle some of our older bikes.

  49. Phoebe says

    Just an FYI…a full article on this motorcycle was printed in the latest issue of Custom Fighters magazine, available through customfighters.com =)

  50. Boog says

    Jay, nice work on bringing the traditional cafe racer style to a monoshock streetfighter bike! I would be interested in your 750 version and how it turns out…

    These old Kaw triples were evil in their day…too bad they were in such crummy chassis. I wanted one when the 750 came out but college and the like got in the way. Eventually settled for a 750 Honda four, and it was a good choice for my needs. Wasn’t as flimsy as the Kaw triple, but being an old 2 stroke fancier, it wasn’t as interesting to me, either.

    Nice work…

  51. loki says

    Great looking,very cool motor and a bike i would own no problem, but how does it handle at speed around the track or road as the fuel load gets lower? The NS 500 Honda was terrible with the underbelly tank.

    I like it in bits and as a whole

  52. C0zmo says

    You absolutely rock. Something like this would sell millions if companies had the balls to build them. Exhaust totally kicks ass.
    Thanks for reclaiming that song, too. It never belonged with Cadillac and the Bonham’s had a good relationship with Kawasaki.

  53. says

    thanks all glad you like it .thanks for posting your thought`s on the bike .the 750 model will be street registered with larger tank and a battery.thanks again .

  54. Reverend D says

    I’m rather astonished so many people find what they think are faults with the bike instead of admiring the craftsmanship and all the things that are right. It’ll get hot for the rider (apparently not, its got shields and the rider isn’t complaining), the fuel tank is in a bad place for possible contact with road debris (oh you mean like the car you go to and fro to work with everyday?), the fuel will slosh around and make it unstable (Um, he mentions fuel cell, as in having foam in the tank which keeps that to a minimum once again the rider seems to have all his hide and the bike is intact, guess its ok). The thing apparently works, its light and the rider digs it, so whats the problem?

  55. Ralph says

    As a long time enthusiast of Kawasaki Triples (I grew up on them) I must say this is an amazing build.

    A major obstacle when modernizing these bikes is dealing with the 3 “voluptuous” expansion chambers. There is almost no good way to route them without ground clearance/cornering issues, or bodily harm issues from the exposed pipes. The Jaybuilt bike takes a radical approach unlike any I have previously seen and succeeds beautifully. Unlike some commentors, I completely understand the reasoning behind the belly tank and applaud this builder for his brilliant problem solving skills.

    Is there any way to get a ride on this beauty? If so, sign me up!

  56. Thom says

    I had a very similar idea to this bike some years ago, after seeing an article on the Bimota Supermono, which also had its gas tank under the engine for lower CG. I planned to use a Suzuki T500 engine and a 1987 CBR600 frame, but same concept. The two chambers of the Suzuki parallel twin would take up a little less space than the three of the Kawasaki, and I would just have used the upper skin of the stock tank as a heat shield. Biggest issueI had with old two-stroke was ground clearance in corners. I figured routing the chambers over the engine would solve that. Glad to see someone else was as crazy as me!

  57. jay says


  58. andy says

    I just found this by coincidence,maybe the lights are already done,if not an LED back light between the exhaust and tailpiece would work and fit I think.Headlights,something small…and for speedo also a small digital unit,then they don’t take away from the design,which is pretty cool!cheers,andy

  59. Dave says

    Hi I’ve just found this & think its a great design. As others said the spannies dont run *that* hot so should be ok under an insulated cover.

    I’d like to see the fuel tank with a curved front end and it does look like the centre pipe will get hit by the front wheel on full bump. That could be solved with a Hossack front end and give even better handling.

    On the subject of strokers, the expansion chambers are tuned to suit the revs where the engine makes max power. Gasses exit the exhaust port with a bang as the port open suddenly (unlike poppet valves that ramp open). The shockwave expands down the diverging cone creating a suction behind it that pulls mixture into the cylinder and down the pipe. the shockwave bounces back of the far end of the chamber and pushes the mixture back into the cylinder just before the port shuts. Due to gas inertia the cylinder is filled from both sides. During the closed period gasses emerge from the stinger pipe.

    The pipe’s overall length is governed by engine speed. Often there is not enough length if they are run out the back of the cylinder. High revs allow a shorter pipe but strokers rarely work above 10,000 rpm.

    All this is about the speed of sound in a hot gas so the temperature and pressure all affect how it works. Add in the porting etc etc and its complex stuff to get working right. All thanks to Walter Kaaden, the guy who designed MZ engines in Eastern Germany after WW2. He never patented his invention and died penniless.

  60. Chris says

    Simply the best looking motorcycle I have ever seen !!! some issues though – I believe that Honda tried a similar fuel cell arragement on one of their 2 stroke GP bikes some years ago but found unslveable centre of gravity issues with the fuel slosshing about so low in the set up. Also Hot Balls ????? Dont mean to nit pick though – I want one !!
    obvious issue here is the expansion chamber routing (forcing the fuell tank under the motor). I am trying to think of a different routing system (so far unsuccessfully) and still retain the BEAUTIFUL effect – any ideas.