Moto Carrera - 2-Stroke & 4-Stroke Sport Bike Specialists

Or, What I Did the Last Two Seasons, as told by Clinton F. Whitehouse

In my ongoing effort to relive the later twentieth century, I moved from an RD400 fetish to an obsession for RZ350's a few years ago. Not completely mind you, as I still have tons of RD stuff. Anyway, Doug (at Moto Carrera), and I decided we wanted to race a more modern class such as 550 Superbike. About two years ago, that required the ability to do at least 1:30xx lap times at Willow's big track. While I think it would be possible for an air-cooled RD to do that, it would take a superhuman effort to do it reliably. So we hatched a scheme to use an RZ350 as we knew it could be coaxed into doing the required lap times at least somewhat reliably.

I had a frame that had been extensively braced by Frank Aragaki that I had acquired by trading a stock RZ radiator. Frank had done 1:30.xx on that frame so I figured it must be built pretty well. Doug foolishly agreed to supply a fully modified Moto Carrera RZ race motor, and I had a 1991/1992 TZ250 that no one was foolish enough to buy, so I used the front end and wheels from the TZ. I also used the beautiful aluminum fuel tank, ugly fairing and mediocre seat. To adapt the front end to the RZ frame, I pressed the RZ steering stem into the TZ triple clamp and used after-market tapered bearings made for the RZ. The weld on the bottom of the RZ stem must be removed either by grinding or turning it in a lathe. You should also cut a grove to put the TZ's c-clip on the bottom. This clip keeps the stem from pulling through the triple clamp. I put 2000 GSXR750 .85 kg./mm springs in the forks to stiffen it up a little. Stock TZ springs are around .70 kg./mm.

I built a new sub-frame to fit the TZ seat, as the person who owned Frank's sub-frame kept it, the dirty rat bastard. As you can see in the pics the TZ tank fit well. One advantage to the TZ tank is that it is shorter than the RZ tank which allows the rider to get more weight on the front wheel, especially if you have a big beer belly.

The hard part was figuring out which swingarm would work. I think Frank used an FZ600 swingarm, but I couldn't beg, borrow, or steal one. So I found an FZR arm at my local salvage yard, Ed's Honda, and decided it had potential. The biggest problem using modern swingarms is their length, the FZR ain't that modern, so it ain't that long, but it is pretty stiff. The FZR arm is about an inch longer than the RZ's, but it's fairly easy to make the adjustment slots longer, and put longer all thread in the axle adjuster blocks. You can shorten the wheelbase back to the stock RZ length this way. A side benefit is you can experiment by making the wheelbase longer. This will put more weight on the front, which might be worth the increase in wheelbase. I haven't experimented with wheelbase length, because of lack of time, but the bike seems well balanced, (unlike the rider) with the adjusters about 1/2 inch further back than the RZ arm would allow. To use the FZR arm you must use the FZR knuckle and shock. The swingarm has to be narrowed and new link dog bones made that are shorter. I just used steel plate to make different lengths of dog bones so I could adjust the ride height. I settled on 119mm. The damper a tight fit, so tight that the spring must be rotated to miss the swingarm cross brace, ( see pics). I had to use a lighter spring than the one that came on my junk yard Ohlin's damper. I am using the 500 lb. (see previous note about beer belly). Since the TZ's 17 x 5.5 inch rim's tire is smaller in diameter, I used shortened dog bones to achieve the stock ride height. This had the added benefit of increasing the swingarm droop which brings the swingarm angle more in line with modern thinking. My unladen droop is about 13 degrees when measured by a Smartlevel.

The TZ wheel with all the stock spacers, caliper holders and such was exactly the same width as the FZR. The only mod required was to weld some 3/8 keystock on the top and bottom of the vertical faces of the swingarm on the brake side to replicate the slot in the TZ swingarm. Since the FZR's arm is steel this is easy. If you use an FZR400 aluminum arm you'll have to be good at welding aluminum, since this slot keeps the caliper from rotating with the wheel. I suppose you could adapt the brake stay arm from the FZR, but I haven't tried it.

You will have to make an offset countershaft sprocket to line up with the TZ's rear wheel sprocket. I did this by turning all the teeth off a 14 tooth RZ sprocket and boring a hole in the 17 tooth sprocket that was about 5mm smaller than the outside diameter of the 14 tooth donor. I then cut a counter bore exactly the outside diameter of the 14 tooth donor. This indexed the sprocket so it's outside remains concentric and square with the splined centerpiece as I welded on both sides. Make sure your inside sprocket is small enough to allow the chain to fit without hitting the weld. The center hole must be big enough to fit the nut and locking tab washer. The rear sprocket must be off-set .250" towards the center of the wheel when using this combination of parts. I just cut the center out of one sprocket and the teeth off another. I then shave off .020" the face about .750" from the outer radius toward the center. I do this to index the outer sprocket before I drill bolt holes to hold the two sprockets together.

The bottom end is stock save for aftermarket plates, springs, PVL ignition system and a Wiseco hot rod crank. This crank is fine but DON'T use the small end bearings that come with it. The top end is from a Banshee ATV. These cylinders don't have power valves which isn't a disadvantage for roadracing as the power valve opens at 6500 rpms. If you're at that low of rpms, DOWNSHIFT!!! Since there aren't any power valves this leaves a lot of room for cooling water around the exhaust port, and that's a good thing as my close friend Martha Stewart would say. The down side is, if you are running RZ cases you will have to plug the bottom of the Banshee's cylinders, as the water jacket is open under the exhaust port. I made some plugs out of square aluminum stock and epoxyed them in. The RZ case blocks about half this hole so they can't pop out. The RZ has no water under the exhaust port, so Yamaha in their infinite wisdom didn't leave much aluminum on the base gasket surface of the RZ case to block this port. On the Banshee, of course, the case's base gasket surface blocks this port. The latest base gasket for the Banshee is nice, and it also works on the RZ cylinders.

Doug got the cylinders ported to TSR specs by his engine builder extraordinaire, Ed Erlenbach, so if you have any questions talk to him at Moto Carrera. They're really nicely done and still pretty conservative in port timing. These cylinders were already 67 mm, so I have been running Vertex pistons.

We started out running an aftermarket o-ring head, but kept burning out the inner o-ring. I think the bore was too close to the o-ring, as the bore was so large. I have since bought a D&D O-ring head since it spaces the o-ring further away from the bore. You can check it out at ddracing.com . I am using 18cc chambers with this head. This gives about 170 lb. of compression. Of course, good race gas is required at this compression. Doug can modify RZ heads, as o-ring heads are hard to come by for the RZ cylinder's.

Carbs are 34mm round slides from a g model TZ. The jets are 320 to 350 mj. I use TZ750 reed boots that are redrilled to bolt onto RZ reeds. We have Carbon-Tech reeds, in the stock blocks.

The PVL ignition does not have an advance-retard curve like the stock RZ. I run 1.8 mm BTDC timing. The rotor on the PVL is not keyed, so you have to be sure both tapers are oil free. Clean them with acetone or something, moonshine maybe. Don't ask me how I know about the oil or the moonshine. The pipes are Doug's RZ pipes that I modified to maximize ground clearance and to fit the Banshee's spigot exhaust.

I am running a TZ radiator because I had it and because it fit in the fairing. If I hadn't owned a TZ rad. I prob. would peruse the junk yard for a better, cheaper one. I'm pretty sure you can't get away with a stocker because even my street RZ runs too hot with the original radiator. PS. I have since adapted aY2K GSXR radiator because the TZ didn't keep up at Willow in the summer.

Even though I don't devote enough time to this fun little project as I run a modern 4 cylinder that takes a lot of attention, we have been reasonably successful. Every time we have finished at the big track we have taken first or second out of a field of thousands of hard core dedicated determined racers (at least ten or fifteen). At the small streets track where it had it's debut in a CCS race, it took second in LW superbike, and fourth in LW GP. I would have won LW sportsman but it showed another of it's achilles heels when it popped it's spark plug cap off. It kept doing this on and for three or four races no matter what kind of caps or plugs I used. I finally clamped the boot to the plug with hose clamps. The next race week-end I raced it in WSMC's F-1 race because it was pouring down rain and I didn't have rain tires for the GSXR. I had brought some old rains from my 250 gp days in 1996. We ran in fifth for the first half of the race but as people got more comfortable in the nasty conditions I got pushed down to eighth. Still, I think this is the first time a street based two stroke has ever taken a top ten in the formula-one class. Starting the next race, the bike dnf'd or filled its over flow bottle a bunch of times while we figured out how to stop making burnt offerings for the o-ring deity. We managed to take a couple of wins even though it was blowing water out the over flow. Then finally in the September 2002 Willow 550SB race we did 1:30.5 and won with the engine running very low compression because we didn't have the new head yet. With the new head we won again in October 2002. I might add the 550SB is pretty competitive out here, with built SV650's and 310cc Aprillia RS250's making up the bulk of the field. The bike is a ball to ride. It feels almost as good as I remember my TZ being. The fact that it makes at least 10hp less then the TZ helps the handling I'm sure. Even with the massive bracing of the frame, it only weighs about 275 lbs, without gas. It doesn't seem to overload the 250 size Dunlop tires at all. We have run a soft compound front and rear at Willow in the summer, even though people say I am insane to do so. PS. So far (6-20-03) I haven't done as well even though I am going faster. I have one second place, three thirds, and one fourth. Oh, and one dnf (remember not to use those Wiseco small end bearings!) Moto Carrera has a new pipe design and new cylinders on the way, so I am hoping I'll start winning again soon.



10424 Burbank Blvd. North Hollywood, CA. 91601 - 818 761-9040 - rdworld@pacbell.net