Background: Although Class C racing has been dead for many years, there are some of us who hold a special place in our hearts for the men and roadracing machines of that era. My personal favorite was the Honda CR-750 followed by the Harley-Davidson XRTT. While the Honda was a graceful, unobtainable thoroughbred, the Harley was almost agricultural in its origins.
A by-product of Harley’s dirt track domination, the XRTT was made famous mostly through Calvin Rayborn’s exploits in England and Mark Brelsford’s surprise win over Kel Carruthers at Loudon. Accomplished on bikes that were flawed at best, these victories came on the interim iron-cylinder XRs. These engines–Harley’s response to the AMA rule-change allowing 750cc OHV motors in Class C racing–were de-stroked 883 Sportster engines. True to their “Waffle Iron “nickname, they generated mostly heat.
The definitive XR-750 engine–which we are familiar with even today–was made from aluminum and was a winner in dirt track almost immediately. Rayborn did win Laguna Seca on one of the new engines in 1973, but with the advent of the 750cc two-stroke racebike, its days as a competitive roadracer were at an end. Sporadic attempts to revive the XR in order to gain a few valuable points for Gary Scott, Jay Springsteen and Scott Parker came to an end when the dirt track and roadracing championships were separated in the 1980s.
The genesis: The aluminum-engine XR-750 presented itself as a blank canvas to the tuners and riders of the early 1970s. While most of the chassis info from its KRTT side-valve predecessor applied in some shape or form, the new OHV engine was a total unknown. One of the early aluminum XR-750s was campaigned by a Midwest dirt tracker named Phil Darcy. Phil was one of those riders who tuned and experimented with his own XR. He raced the bike mostly on the bullrings of the American Midwest for a few seasons, eventually realizing like Bill Werner that his talents lay in tuning the twin. He eventually settled in Haltom City, Texas and started Darcy Racing. Darcy Racing is one of those shops that specializes in tuning dirt track machinery. His work with XR-750 and Rotax motors is universally respected. Although you rarely see evidence of this fact, his handiwork is present in most of the top-level dirt trackers in the country. While Phil was building his business and his reputation, his XR sat, in pieces on a shelf in his shop gathering dust– hardly a fitting end to an old warrior. The year was 1994.
The small industrial park in which Phil’s shop is located is kind of a Mecca to North Texas racers. Across the drive, Ty Howard and his dad Leland had a shop where they were building Ty’s dirt track bikes and beginning to dabble in roadracing. (Ty finished 8th in this year’s Daytona 200.) Behind him were the shops of Bonneville record holders Mabry Racing and their rider, multi-time Battle of the Twins winner Jon Minnono. In the middle of all this history in the making was TM Motorsport. Owned by Bob Stevenson, TM built bikes for his son Micah to compete on in CMRA roadracing. TM’s stable included a Woods-Rotax SJ676, a Ducati 750SS, a Ducati 851, a Honda Ascot 500 and a Honda CBR600. Several dirt trackers and MX bikes were thrown in for good measure. Micah had finished the previous year as a multi-class CMRA champion as well as winning a WERA championship in the Clubman Novice class. He rode the AHRMA races at Daytona as well as the entire Sound of Singles championship series, finishing second. Phil Darcy built the 676cc engine for the Woods-Rotax. Bob was always looking for a new project and one day while over bugging Darcy next door, he came across the remains of the XR-750.
A pile of parts and a picture on the wall: I had originally met Bob Stevenson in 1993 at the local Ducati shop where he and I had the dubious distinction of being the only two 1993 Ducati 7500SS owners in Fort Worth. He asked me if I wanted to restore a BSA 650 dirt tracker he had acquired and I, not knowing anything about BSA motors, jumped on the project. I raced that and the Honda 500 for a short painful period and decided that my talents lay elsewhere. The XR project lay there fermenting in Bob’s mind for months. I had a copy of Allen Girdler’s XR-750 book and access to a process (enlarging) camera at the government facility via my day job. Girdlers’ book had a line drawing of an XR-750 roadracer that I blew up to life size and hung on the wall as inspiration or, depending on the day, in opposition to the stillborn XR project. The on/off nature of the project continued until November 1994. I was at home when Bob called and told me he had finally bought the XR and we were going to race it at Daytona—in four months! We would do the chassis and Darcy would do the motor. Simple.
Welcome back, my friends, to the thrash that never ends: We got started, and it soon became apparent that this wasn’t nearly as simple as we had imagined. There were, at the time, two avenues. A guy in Ohio runs a shop that restores XRs and had for sale a complete XRTT rolling chassis. First, this would have been too simple and second, he wanted a king’s ransom for it, or so we thought for it. If we had only known how much it would cost and how hard it would be. So, we took the path of fools and started to build it from scratch. No one part of the project was overly difficult. But, as they say, the whole is a sum of the parts. Here they are:
At first, we had thought of building a pseudo-road acer, kind of a dirt tracker with clip-ons, good tires and brakes. We quickly discarded this notion and went about building a proper XRTT. This would require modifying the frame so the thing would handle (?) and the ‘glasswork would fit. The XRTT frame was subtly different from the dirt track version with the exception of the steering head area. This area of the frame was dropped several inches and raked out. To facilitate the changes we called Jeff Coles at C&J out in California. After determining what we wanted to do was feasible and coming to terms, the frame was shipped to Jeff and he started the transformation of the duck into the swan. While the frame was gone, we started to acquire the bits and pieces needed.
AirTech has been the savior of many a vintage project. They are always on the lookout for interesting and unique fairings and tanks to pull molds from. Team Obsolete had several types of XRTT fairings, tanks and seats and had allowed AirTech to copy them. This variety grew from the work done on the KRTT by the Wixom brothers in the Caltech wind tunnel prior to the 1968 season. Wixom developed true modern streamlining for the KR and it took Cal Rayborn to two consecutive Daytona 200 victories. They developed both short-course and super-speedway streamlining packages. We decided to use the super-speedway fairing and tank. Micah was a fairly small rider, and we figured the bigger the fairing, the more he could tuck in out of the slipstream and the faster we would go. We ordered these up and when they arrived, we were amazed at how big the fairing was. Had we ordered one for an Electra Glide by mistake? It was interesting to see faint lines in the ‘glass where edges of the original paint job on the Team Obsolete fairing were. This made it easy to lay out the paint later on. Mounts were made and the ‘glass was set aside, waiting for paint. Time went by slowly.
Wheels, brakes and suspension
AHRMA rules are very clear as to what can and cannot be used on vintage racebikes. We decided to build the bike to the limit of the rules, yet retain the look. At first, Bob and I were thinking of building a dual-disc CB-750 front wheel like the Harley factory bikes used. This proved to be more difficult that we thought. After several weeks of searching, we found out two things, Honda 750s had 40 spoke front wheels and it was hard to get good rims for them and you couldn’t find CB-750 brake parts that were usable at salvage yards, We decided that if we were going to build wheels from new parts, then we were going to use good stuff, not retread early 70’s Honda parts. A call went out to Kosman Specialties. They built us two wheel-and-brake setups that took the rules to the edge, but not over. They sourced a set of Marozzochi 38mm forks and built a beautiful set of triple clamps and caliper mounts for them. They modified the swing arm to accommodate their wheel and caliper and sent along an assortment of gearing. This was the best part of the project. Everything bolted right up to the frame without a hitch. Works Performance provided the rear shocks. So, there we were in late January. We had a rolling chassis and bodywork, but no lump.
Phil Darcy up to this point had been so absorbed in getting a multitude of Rotax 600s ready for the Daytona short track and doing Supersport-legal valve seats for 600s that he had sort of forgotten us next door. So when we showed up looking for our motor, there it still sat, in pieces on the shelf. Phil had thought we weren’t going to get it done and had concentrated on his PAYING customers like a good businessman should. Anyway, here we were less than two weeks from leaving for the warm-up at Roebling Road and no engine. Phil hit the ground running and within a couple of days had built the lower end. He warned me that the cases were old and we couldn’t build as much horsepower into it as a new D-port mile motor could handle. These cases would come back to haunt us later. With a week to go, Phil rolled the motor over and dropped the bombshell on all of us: an XR engine has no internal oil passages. There are a multitude of external oil lines that have to be fitted and safety-wired. This, plus the fact that we had to fabricate new engine mounting plates due to the frame mods, put us into 24/7 mode. What we had not realized was that on an XR, the engine, not the frame, is the central mounting point for almost everything. The rear sets, master cylinder, battery, lower steering damper mount, the list went on forever. Also, the pipes showed up as a kit, which just about shut down the whole project. Luckily, Bob had decided to hire some help. Poor Les White didn’t know what he had walked into when he showed up. He immediately fabricated the wiring harness and sorted out the carbs as we dug in and fabricated all the bits that would fit. Concurrently, we had to lay out the paintwork for the painters and get it moving. We matched the factory bikes of the early 70s and had stickers made to match their graphics. It was Sunday evening and the bike was scheduled to leave on Tuesday afternoon for Roebling. We worked through the night and the next day, getting the bike done early Tuesday morning. After test fitting the bodywork, we rolled it over to Darcy’s shop and hooked it up to the dyno.
The moment of truth, part I: the dyno
Phil had a chassis dyno for measuring rear-wheel horsepower. We set it up and, after a few aborted attempts, the big twin came to life. Phil had put one of his electronic ignitions on the bike and had modified the heads for two plugs each. We were running a total loss electrical system and, in the interest of using a convenient, already-existent battery box, we fit a small 12-volt battery. This would come back to haunt us, also. The dyno told us that the bike was strong, but was not going to win any horsepower battles against the Honda and BSA/Triumph multis we expected to run against at Daytona. It put out 85 rear-wheel horsepower–this compared to the 100-plus horsepower that a modern fresh XR-750 is capable of. Still, for a 20+-year-old bike, it ran fine and Phil was satisfied with it. His final warning was, “Don’t over rev it or you will be looking for a place to stop with the rear wheel covered in oil.” The bike was rolled into the trailer along with the Rotax and the two Ducatis at 5PM on Tuesday. We left for Daytona within the hour.
The moment of truth, part II: Roebling Road
I had to work on Wednesday (oh yeah, my real job) so Micah and I left for Roebling Road on Thursday morning at 4 AM. We needed to be in Savannah by 7AM the next morning. As we traveled from North Central Texas, the topic of the conversation never seemed to center on the XR. It was like he was ignoring it. The XR was our project. Micah had done some of the assembly work, but never really voiced an opinion either way. That would change soon. We got to Savannah around 11 PM that evening and were greeted the next morning by Bob hammering on our hotel room door and shouting something about leaving us if we didn’t get up. AHRMA Tech at Roebling opened at 7AM and he didn’t want to be late.
Roebling Road is located in the middle of a neighborhood and there are restrictions on noise and when it can be made. Tech went smoothly and after allowing them to find the one glaring error you always leave so they won’t find all the little ones, we passed. Later in the day, we wouldn’t be so lucky. I gave the bike a break-in by cruising it around the perimeter road for a few minutes. We put it on the charger and waited for practice. The Harley was actually a sideshow at this point. Micah was riding the whole AHRMA Sound of Singles series that year on the Rotax, and the Battle of the Twins championship on the Ducati 750. The Ducati had been prepped by Eurosport Cycles in Fort Worth and the Rotax by us. We set about getting them up to speed and trying to make the Ducati 851 do anything except try to high-side Micah. When it finally came time to run the Harley, we discovered a fundamental engine set-up mistake we had made that even Darcy had missed: Dirt track XR-750s run a considerably lower primary ratio than the XRTT did. The thing was good for about 110 MPH and that was it. We hurriedly put on the tallest gearing we had and went back out. It was a little better but, still, Micah was zinging the motor well above the limit Phil had set.
After practice, the issue with the old engine cases came to light. XRs have sand-cast cases, hence they are very porous. This is all fine and dandy on dirt tracks. Oil and dirt make traction. On a roadracing course, this is not a good thing. I stripped the lower fairing off and used a can of contact cleaner to wash off the cases and the inside of the fairing. I then fashioned a diaper from shop rags and duct tape to keep the bike from weeping too much. This is a drill that would be repeated many times in the next few days. With all this going on, there wasn’t much time to debrief Micah about the Harley’s handling manners. He had remained quiet and just gone about his business in his usual quiet manner.
The races came and went as the day wore on. The Harley was in the last race of the day, Formula 750. Micah finished in the top 5 in both the Singles and the twins races. We parked the 851 for the week for lack of a handle on its ill manners. The F-750 race finally came around. I had not had a chance to see the Harley on the track until that race. It sounded beautiful. The fact that it was over revving helped the effect. Micah ended up 10th giving away many MPH on the long Roebling straightaway. Before the race was over, Bob had called Kosman and ordered the smallest rear and the biggest countershaft sprockets they had to be drop shipped to our hotel in Deland.
AHRMA had tech for Daytona at Roebling. I took the bike straight from the F-750 race, cleaned the oil out of the fairing and off the motor and rolled it into the tech line. I expected no issues as I had cured the morning’s transgressions. I was in line behind one of the guys from Barber Dairies and if you ever want to see a bike that makes anything you have look like crap, check out their race bikes. When I got to the head of the line, the inspector decided that our sleek streamlined big fairing bike was a little too streamlined. He decided that the cutouts for the controls were not big enough and sent me back to chop up our beautiful paintwork. Two trips later, I got it right and we were on our way to Daytona. As Micah and I pulled out of the pits at Roebling and drove into the Georgia sunset, I asked him what he thought of the day. He said it had gone well and he was looking forward to Daytona. I finally asked him about the Harley and how it had worked. He looked at me and with a completely straight face, said “Rick, that thing handles like a God-damn party barge”. This was as expressive as this kid ever got. From then on, the noble XRTT was the Party Barge.
The moment of truth, part III: Daytona
We would be running the Harley in the F-750 class at Daytona. With tech inspection taken care of at Roebling and the tallest gearing we could get already installed on the bike, there was little to do until practice began. During practice, a strange misfire started and got progressively worse. We of little electrical knowledge decided that the battery was going flat and charged it up. Team Obsolete was pitted next to us and graciously loaned us an extension cord. Thinking we had the problem solved, we concentrated on the other twins and the single. Then, when we went to fire up the XR for its race, it wouldn’t run on the front cylinder. I sent Micah out to the grid hoping it would clean out and start running right. About this time, either Bob or I got the idea that maybe it wasn’t the battery, but the load we were putting on it. We had the dual plug heads and both sets of coils on the bike. I decided that if we only ran one set of coils maybe it would act right. I ran as fast as I could back to the pits and grabbed the single coil plugs wires and caught Micah before he could leave on the warm-up lap. We got the wires changed and sent him out for the race.
It worked. The bike ran fine and Micah got a great start, probably due to our low gearing. He ran consistently in the top 5 until the superior top-end of the BSA/Triumphs and the Hondas slowly ate him up. He ended up 10th. Standing there on pit road with a set of plug wires draped around my neck while that thing went by lap after lap, and knowing how close we came to not being there at all, was a blast.
The win: Texas World
Bob had always said I should race the XR at a CMRA race, but having severely damaged my shoulders racing the year before, it was no longer an option. He and Micah took the XR out twice more that year. Once to Texas World Speedway where they won the Vintage Class and once to the AHRMA race at Mid-Ohio where a local rode it after Micah got hurt on his Single. Other than that, the bike was once again relegated to dust collecting.
The next year, we were a lot more serious about racing. Micah had an AMA expert license, and we had also picked up a Kawasaki 600 and a new Suzuki GSX-R750. After prepping all the bikes and the stuff for the modern AHRMA classes, we decided to dust off the XR. We took it over to Phil, he installed proper roadracing primary gearing, and gave it the once-over. He once again warned us to respect the ancient engine cases and sent us on our merry, ignorant way.
The bike ran well in practice and was parked at a display for American racing motorcycles in the infield. After lunch, we went over to retrieve it and met a group of Italians who were shopping for bikes. They asked if I was interested in selling the XR. I told them to follow me and we would talk to Bob. We tried but, in the end, it slipped that it was a warmed-over dirt tracker, and they lost interest.
The race went from good to poor in the course of a gust of wind. Micah got a good start and was running in the top 5 when a gust of wind caught that big old fairing coming out of NASCAR Turn 4 and sent him straight towards the supercross track at top speed. He told me later that all he could think about was how far he was going to fly if he hit one of those berms or jumps. He managed to steer onto pit road and, after a slow lap, retired. At that point, the Party Barge was beached and thought of no more. Micah finished third behind Alan Cathcart and some Euro in the Sound of Singles race. The Suzuki had rod problems, and we didn’t qualify for the 200, but we did make it into the 750 Supersport race. Micah did one lap and parked it. The 600 Supersport race was run briefly in the rain and he was in the Top 20 when smarter minds took over and red-flagged the race. I left that afternoon and went home. The next year, the Harley and I stayed home, but Micah qualified for the 200 and ended up finishing 31st.
Bob soon traded the Harley to a guy from Austria or Australia or somewhere for a couple of old Ducatis. I hope the guy hasn’t found the limits of those ancient engine cases and isn’t too tired of washing out the fairing every time he runs the engine.