SECApocalypse - 1981 XJ750 SECA "Mad Max" bike

Had a thread for this already, but its OOOOOOOOOLD. Took me 4 years to build, and even folks who saw some of the early stages were surprised at what it now looks like. Front end is an adjustable Hossack style setup with 4.5" travel (forget the wheel rate, think its about 300 / in), back end uses the shock from a BMW r1200 Montauk with what amounts to a high leverage ratio, has 3.5 travel and wheel rate starts at 250 lbs / in going up to 45o lbs at end to travel (so a bit stiffer than stock, to MUCH stiffer)

Bike actually starts VERY nicely, just choke and throttle and BOOM, catches on the first turn. But once it warms up I have to turn the choke down and then its hard to start (needs ether) and won't idle unless I rev it a bit. Probably just needs normal tuning (timing / spark plugs / valve clearance), carbs should not be a problem though - they were well cleaned when the bike was torn down and then sealed up and stored inside. Despite the looks, the breathing from the carbs perspective should be near stock- the custom airbox has the same volume as stock (including the filter / snorkle protrusion) and the stock snorkle sits in a plate under that air filter, so all air that goes into the box has to pass through it.

Because of tuning, I haven't ridden it far yet, maybe a mile going around the neighborhood. Handling seems good, and the front brakes work GREAT (is the stock MC and rotors, with R6 calipers). Rear end seemed a bit freaky when braking, but I think that is because the tires is old and I was on a freshly surfaced road, plus there's now much less weight on the back end. Total weight is 500lbs dry, 265 front / 235 rear. I weigh 225, am 6'3" and have a long torso (hence the ergos) so a lot of my weight is also on the front.

 

do you put gas in that 2nd tank?
Oh, and my original thought.. ."What on earth?!"

 

The rear 'tank' is just a fender. Is the original, was very badly rusted. Bottom is cut out and inside sprayed with undercoat. The chain lock that Yamah aincluded with the bike (matching keys) runs through the fuel port and then around the frame, for use as a helmet lock.

Replacement tank is a from a Virago 750, has the battery mounted under it just forward of the seat. It's pretty much a straight swap, you just have to lift the rear end of the tank up maybe 4 inches (cut off orignal mount and welded it to a bar coming up) and plug the right side petcock port (no idea why it has two, I just welded a patch over it).

It looks pretty crazy, but should qualify as street legal. Turn signals are not required in my state, but it has em (though they are not currently wired up). The plate holder is LED and has brake, plate, and turn lights, and the headlights have small bulbs below the actual beam bulbs that can be set up as turn signals without much work (they are meant to be low-brightness aux lights). Even has a working horn (I beleive it might even be the stock unit).

The custom construction... would technically require a inspection and special registration or even a new VIN. I'm not gonna mention it at the DMV (the old VIN is still there, I didn't hack the neck any or weld to that part). Its been legitmately load tested (using a frame stand, turnbuckle, and crane scale) but I don't wanna argue with some half-informed DMV desk jockey about what a Hossack front end is.

Technically I didn't even alter the frame much... just welded & bolted some stuff to it. Like a bolting on whole new front steering & suspension setup. Which Is actually not THAT uncommon - trike conversions often work the same way.

 

I am left dumbfounded and speechless......but I think you do deserve some type of award!

 

How fast were you going when you hit that deer?

 

Whow....., I mean wow!

 

I like..

1) The mono-shock conversion
2) The airbox work around

 

That is a unique machine sebwiers where on earth are you, I'd need an engineers report for that to be legal in Aus'. I do kinda like it's one offness, it's your boat and I hope you float very happily on it.

 

I'm in Minnesota, USA.

I have no idea what the legal impact of the mods is, and may end up talking to a lawyer through a local bike group. There's a few ways to get custom build vehicles on the road here. The simplest is just to never mention the modifications when registering it, and leave the VIN stock. There's not any inspection when you just go to get a plate for an existing bike; its up to police on the road to cite you for issues. That was my plan, though its probably not strictly legal (the do ask if you altered the frame). If I get stopped by the wrong officer, it could be a big problem, but I figure if I ride cautiously and play it off as a serious and well researched engineering project (which it is, just with some art thrown in) when questioned, I should be OK. I've been told by others with similar projects that police are usually just curious, and maybe want a picture.

 

I was following your old build thread, and wondered what had happened to this project. I've been intrigued by the Hossack suspension setup for years but don't have the guts (or skills) to actually build one myself. Please get this thing tuned up and on the road so you can give us a real ride report on how it handles!

 

That's proving a bit challenging. Probably need to pull the carbs off and make sure they are 100%. Plus the $#@^& throttle cable issue pretty much stop any tuning before I can run it more than 2 seconds.

I did actually find a (very good) local shop that was willing (eager even) to take it on after seeing pictures and a video of it running. One other did not respond, and a second responded to say it would be impossible to tune because of the mods... without even knowing what the airbox setup was.

If I can find the money, I might just hand it off, because this is a very frustrating stage for me, and not my area of skills.

 

Where in MN? I'm down in Rochester.

 

Saint Paul.

I actually found a local shop to do my carbs. The advice on this site could probably get me through it, but I lack the time, patience, experience, and equipment to get the job done reliably before I need the bike running for an event in California.

 

Good luck with the shop... make sure to provide them with the address to "Church", along with contact info for Father Chacal. Lol

 

The virago 750 tanks had two petcocks because of the tunnel design of the tank. If you block off one side your only going to get fuel from the side with the petcock on it. I learned this the hard way. I have a virago 750 tank on my virago 920. The virago 920 only has one petcock.

 

Would you mind if I merged the two threads so people can see where the project started?

 

Well, the rear fender is just so obvious but brilliant! Never have seen it before despite it's obvious application...said tongue-in-cheek but good for you for seeing so far outside the box. I love the front end because mods that serve no function just aren't my thing but kudos on your build!

jeff

 

The antlers are to help him win the best mate during The Rut.

 

I'm very interested in your airbox mod here. There a build thread?

 

Nah, I guess not. I just got the bike back from the mechanics and have put about 70 miles on it, seems a good time to wrap up. I paid a whopping $650 to have the carbs rebuilt and the bike lambda balanced and dyno tuned; it makes 55 rear wheel horse on the rolling road. Might make more with a better pipe, apparently the cheap aftermarket MAC muffler that came with the 4-1 system the bike came with is a bit restrictive. I can't imagine what a less restrictive muffler would sound like; this one is pretty lout by my standards.
The runs GREAT, no stumbles, so I think money well spent, especially gioven I was in a rush to get it done and had no idea what was worng (it started but would run super hot and rev high or die). I had to contact 3 shops finding somebody willing to take the job on, most said it would never run. The old guy who did the work had me put the dyno video on his web page to prove to the other shops that yes, it WOULD in fact run.

Not really. Is pretty basic work (the first glass work I've ever done). I built a form out of styrofoam that would be the interior volume of the box (insuring this volume nearly matched the stock volume, I think its about 130 cubic inches), and covered that with packing tape. I covered it with layers of prickly fibers and nasty goop until I thought it was air tight. I took a bit of care at the front where the carbs would go; this was left with an open area big enough for all the boots, and the whole mess was set to dry each time with this area face down on a flat plastic surface, so that it had a flat, smooth front. To mount the carb boots, I made a plate from 1/16" aluminum that was the shape of this opening and had 2" diameter holes drilled in the pattern needed for the boots. It simply tapes to the fiberglass using high temp aluminum tape for furnace work. There is a 4" diamter PVC pipe coming out of the other end of the box. The mouth of the pipe is covered with a 1/8" aluminum circular plate that has an oblong hole cut in it for the stock air intake "snorkle"; combined with the stock volume, the airbox resonance (if not flow) should be the same as stock. The PVC pipe itself has a 4" cone style washable filter slipped over it.

The pictures are in this album, with some descriptions. There's actually a laser cut acrylic plastic plate in the airbox that I was gonna put the boots in, but I figured out pretty fast that was not gonna work. https://imgur.com/a/GzIm0