650sx build by: my650sux

[Joe Dart]

So this ski has been in the family for a long time, I have been ridding it way before I was legal to do so. Dad gave it me and I started making a few changes. Mods include: bilge pump, dual pissers, finger throttle, water box 5 hole mod, PJS exhaust, Octane intake manifold, Keihin 44mm carb, Boyesen dual reeds, K&N Filter, oil block off plate, Summit Racing high temp silicone coupler, T-Bolt clamps, Blowson 0 degree bars, Pole spring, ODI grips, Blowson footholds, Hydro turf, Blowson freestyle cone, Impros 9/15 hooker prop, D-cut WestCost ride plate, werx scoop intake grate and new aluminum tow eyelets.

Future plans: I picked up a wetjet for cheap and plan on throwing the 701 61x into the ski, I just can't decide if I should start before Carolina Beach Free Ride. I have the ski running great at the moment and don't want to risk a break down after driving seven hours. I also plan on putting a scupper valve on the ski because subs and fountains make the ski take on lots of water, leading to a dead battery.

Below are some pictures of my build, I'm sure some haters will say WHY?? It's a 650sx... This wasn't my first ski (js440) but it was one of the first and I plan on keeping it even after I make the jump to an after market hull. I am going to back flip this turd before I do it though. I know, It can't be done! I just hope for some good surf to help me out.

 

[Joe Dart]

 

[Vumad]

Good work. Clean finish.

 

[Joe Dart]

So I ordered the Rhaas conversion kit and plan on doing the swap this weekend. I got the old 701 running by pooring a small amount of mixed gas into the top of the carb so looks like the fuel pump is gummed up. I will sonic clean the carb and pull both motors this weekend. I plan on trying to run the wetjet wescost exhaust pipe and rotating the cone to line up with the factory sx waterbox. I plan on using everything from the wetjet electronics wise so I will have a strong running 650 complete swap on the market soon. I will sell everything that comes out of my ski: motor, ebox, start/stop, coil, 44mm carb, intake, pjs exhaust, base plate and motor mounts. Anyone in the market?? Fair price to sell the engine swap??

 

[swaggggg]

So I ordered the Rhaas conversion kit and plan on doing the swap this weekend. I got the old 701 running by pooring a small amount of mixed gas into the top of the carb so looks like the fuel pump is gummed up. I will sonic clean the carb and pull both motors this weekend. I plan on trying to run the wetjet wescost exhaust pipe and rotating the cone to line up with the factory sx waterbox. I plan on using everything from the wetjet electronics wise so I will have a strong running 650 complete swap on the market soon. I will sell everything that comes out of my ski: motor, ebox, start/stop, coil, 44mm carb, intake, pjs exhaust, base plate and motor mounts. Anyone in the market?? Fair price to sell the engine swap??

what's the price for the 650? Motor and everything

 

[motobehrens]

Cool project, but you won't find much love for the 650 on this site. A couple things to keep in mind; The oem handlepole is ridiculously heavy at about 16lbs with no chinpad or hardware, compared to about 8lbs for an sj pole. That's alot of weight to be carrying that high on a ski. I'd be looking for an aftermarket aluminum or an oem SJ pole to throw on this ski. Same with the OEM waterbox, which is twice the weight of an SJ box. The cool thing about these hulls is that they are practically free, and there is plenty of room to put full SJ internals.

 

[Joe Dart]

@swaggggg There is another guy on here that is interested in the complete swap, If he doesn't pick it up I will PM you. I want to wait until after Carolina free ride to do my swap (Oct 1st-4th). Because I have never seen the whole deal for sale I have no idea what to ask. I'm open to offers. All the mods on the engine come with it. Intake, carb, exhaust, reeds, K&N, start stop, baseplate, motor mounts, cdi, coils, starter, bla bla bla

 

[Joe Dart]

@motobehrens Thanks man, I am actually a pipe welder so I think I'm going to fab an aluminum pole for the ski. I didn't realize they are 16lbs, that's a lot of weight high off the water. I did the water box mod when I had the engine out and I agree that thing weighs a ton. Does a superjet water box sit in the same place, very front of the ski? Same set up with inlet and outlet on the same side? I figured it would be completely different because of the rear exit exhaust.

 

[Midlake Crisis]

@motobehrens Thanks man, I am actually a pipe welder so I think I'm going to fab an aluminum pole for the ski. I didn't realize they are 16lbs, that's a lot of weight high off the water. I did the water box mod when I had the engine out and I agree that thing weighs a ton. Does a superjet water box sit in the same place, very front of the ski? Same set up with inlet and outlet on the same side? I figured it would be completely different because of the rear exit exhaust.

Waterbox is way different on Superjet. I would like to see what you come up with for a pole.

 

[motobehrens]

@motobehrens Thanks man, I am actually a pipe welder so I think I'm going to fab an aluminum pole for the ski. I didn't realize they are 16lbs, that's a lot of weight high off the water. I did the water box mod when I had the engine out and I agree that thing weighs a ton. Does a superjet water box sit in the same place, very front of the ski? Same set up with inlet and outlet on the same side? I figured it would be completely different because of the rear exit exhaust.

Superjet waterbox exits on the right side of the ski, so you would have to run a front side exhaust off the right, or just set it up like an SJ and install an Al or SS exhaust tube through the back of the ski and make it rear exhaust. Should be easy enough if you're a pipe welder. I would use the RN Aluminum box, RN long rubber exhaust tube, and an Aluminum rear exhaust tube of the correct diameter.

 

[Vumad]

I wouldnt bother with the sj box unless you are running a 750 motor with a big pipe. I dont think you will get returns worth the hassle with a 650 pipe.

The sj box on my x2 was the best it ever ran. I have a decent amount more motor. I think you could run a sj box with a front exhaust on a x2 between the carbs and the battery. 650sx has a similar space if i recall. Rear exhaust is great and should be a good fit on the sx. X2 is very tight and it wont even stay up as is so taking that foam out on a x2 is very sketchy.

 

[Joe Dart]

Thanks for the input, I'm definitely going to look into the sj exhaust. The sx waterbox is stainless and very heavy as you all stated. I rode a 760 square nose at Carolina freeride and was amazed with the power. Now I have started reading the two stroke tuning handbook, which makes me want to build a motor. I'm in trouble

 

[Midlake Crisis]

You making any progress on this? I am thinking about doing the same, or else buying a 750 or 800 to drop in.

 

[Joe Dart]

Well, I have all the parts I need to do the swap and have the two skis sitting beside each other in the garage. I have been on a crazy work schedule here lately and haven't had time to mess with it.

 

[Joe Dart]

So I got a little time off work and pulled my wetjet apart. I'm one step closer. Here's a couple pics of my mess

 

[Joe Dart]

Here is a youtube link to the engine running before pulling it out.

 

[Joe Dart]

I spent a night with a friend pulling the 650 engine and bolting in the 701. Most of my time was spent modifying the wetjet westcost pipe to work with my hull. I ended up running out of argon so, I will have to finish the welding after I get my bottle filled. The pipe had two v-clamps but the lower one had to be removed, the pipe was hitting the hull. By removing this lower v-clamp I saved two inches. I had to cut the large part of the expansion chamber twice making a tapered piece that I could rotate until the angles were right. It's a tight fit in my hull and the water jackets took some time to weld up after removing the lower clamp but, they will still work. I will have to make one more fit on the exhaust when I find a piece of aluminum pipe the right diameter to fit into the factory water box. The wetjet uses a larger diameter rubber hose. Also the bracket that bolts the heavy exhaust to the top of the head will need some fab work. some pictures of my work below.

 

[Joe Dart]

a couple more pics that my buddy took during the cutting and welding.

 

[Joe Dart]

well I kinda had to back up and punt on the exhaust, it was going to be to low the way I tacked it up and I was worried that it was going to fill up with water. I thought about changing the water box to a superjet and running rear exhaust but it seems like a lot more money and effort to do this. I think that I came up with a better solution to the problem. I changed the angle of the expansion chamber but used all the pieces in the order they originally were put together. By cutting wedges out of the chamber I was able to rotate them and get the angles that I needed to meet up with the factory exhaust piping. I welded the pipe on the inside first then background on the outside and welded it. The only thing I need to do now is drill and tap some new water squirt fittings into the pipe and replace the tip of the stinger with a piece of 1.75" aluminum pipe. I am not sure how it will run because I know the shape of the expansion chamber has a huge effect on the way a 2stroke runs. My thinking is that because the taper of the pipe is that same and the length is the same it should be close to the same but I really don't know. Either way, it was free to do and somewhat of an experiment.

 

[Joe Dart]

So, I worked on the ski a little more this weekend. I made a four chamber water box that has twice the area of a 1.75" exhaust pipe. I think it will flow well and should be decently quiet having four chambers. I also did the math and it should be 8.5lbs lighter than the stock stainless waterbox. Also got into the ebox and removed wires that I wouldn't need (fuel level, oil level light, and actual gauge). Removed the fire extinguisher mount and replaced it with an ebox mount. I also removed the pole and bars, I plan on making one. I also plan on relocating the battery to the back of the engine compartment with a custom tray and making a fuel cell that holds three gallons vs. five. I ran out of argon and didn't get to finish welding the waterbox but here are some pictures of my work. because I wanted all of the baffles to be completely welded in, I had to build the box in little sections then assemble it.
Here are my plans and math if anyone is interested, please note that I decided to make the inside of the waterbox flow like a 4" pipe vs. the math showing a 2" pipe. I couldn't find much information on the flow of water though water chambers so I just guessed that it was about half of that of an empty chamber. The new water box should be 3lbs 11.7oz (calculated off the density of t-6 aluminum) with out any water and would hold up to 2lbs 12.8oz of water when filled to the tops of the baffles.