1981XS
XS650 Member
1981 XS650 Café Racer Project:
I’m hoping this post will help someone with their project. During the build I ran into several problems that should have been easy to solve but weren’t. Here’s what worked for me:
Bought my 1981 XS650 Special II brand new in 1980. In 40 years it’s never been dropped, always garage kept, and in pristine condition. I started the project in 2010 and finished this week - it hasn’t always been my first priority. I'd replaced the original Keihin’s with a pair of Mikuni flat-slides - a great upgrade at the time. All else (except wear items) was original. Total miles were about 24k. A friend mentioned Café Racer Magazine, and that the XS650 was a favorite for café builds. Add my love for the look (not the reliability) of old British bikes, and I had to take the plunge.
Rule #1 was that no part of the frame would be cut or welded. The bike was in such good condition I wanted to leave the door open to restore it to original spec. I saved all original parts. The final result would have been better looking if I’d removed the numerous mounting tabs, etc., but…
I stripped as much weight as I could, omitting the center stand, starter, battery, and fenders. I replaced the wheels with lighter rims and tires, the gas tank with an aluminum tank, the rear seat with an aluminum/fiberglass seat and cowl, the handlebars with aluminum clip-ons, the original pegs with a pair of aluminum rearsets, and a lightweight drilled front brake rotor. I replaced the original exhaust system with a 2-into-1 header and a new lightweight stainless steel muffler.
Step #1 was strip the bike down to nothing and powder-coat the frame. I should have masked the serial # first, as I found out when trying to get it registered. Rookie mistake.
The original engine had always pushed a lot more exhaust pressure out one pipe than the other, even though cylinder compression was closely matched and the carbs were synched precisely, so I decided as long as I had the engine out I’d rebuild it. I ported and polished the heads, installed new rings and pistons with stock sizes. I replaced the valve seals, and glass-beaded and lapped the valves. I replaced all crank, rod and camshaft bearings, etc. I’ve used Amsoil in the engine since it had 500 miles on it, so there was no wear on anything (except the cam chain guide, which had nearly disintegrated), but as long as I had it apart I figured I should do it all. I considered a 255 degree crank conversion or punching out the engine to a 750, but elected to keep it simple. I replaced all bearings, seals, gaskets, O-Rings, etc.
Regarding suspension and chassis, I replaced all bushings and bearings, installed Tommaselli adjustable aluminum clip-on handlebars (love these), and had TAB Classics make me a fantastically beautiful aluminum Manx-style gas tank with a flush cap and a single seat/rear cowl (these were so beautiful that I scrapped my original plan to paint this bike, and instead went with an aluminum/stainless steel/black color scheme). The tank has the factory-style front mounts, but I had to fabricate a mounting system for the rear of the tank, and I installed a pair of old-style Ducati petcocks w/ ¼” outlets. I fabricated a seat from a bottom layer of 2” moderate-density foam, a top layer of 2” memory foam, and I subbed out the leather seatcover locally. I fabricated various aluminum mounting plates for the new aluminum rearsets, the taillight, and the headlight angle-adjuster. I used Race-Tech parts and pieces to rebuild the front forks and replace the rear shocks. I changed the tire and wheel sizes, using a slightly larger diameter/slightly narrower width rear wheel than stock, and a slightly smaller diameter/slightly wider front wheel than stock. I lowered the rear shock slightly to adjust the rake angle of the suspension, increasing the positive caster to make the bike a bit more stable at higher speeds (highway speeds here in NM are 75mph, which has that 650 engine working hard. I’m not anxious to experience any tank-slappers at high speed).
The original electrical system (charging and ignition) was hammered after 30 years. For controls I went with Purpose Built Moto for micro-switches and lighting. I originally bought a Hugh’s Handbuilt full ignition/charging system, but it didn’t work. After 7 years of flat-rate wrenching and working on vehicles for 50 years, specializing in electrical systems, I had a good idea what to look for, but I couldn’t get it to go. Tried to get help (or any answer at all) from HHB with no luck. Since I’d waited 2 years before installing the system, it was out of warranty. Regardless, I’m done with HHB. I changed course and ordered a Vape ignition system from Dan at RE-MX. He answered all my questions, and his answers turned out to be dead-nuts accurate. The Vape is a fantastic ignition and charging system! I also got an ultra-lightweight lithium battery to power the LED headlight/turnsignals/brake light and horn. I tried the first and fourth options for setting the advance curve on the Vape, but the fourth was a bit too "smooth". I went with the first (original) setting which gave me the kind of kick in the ass I was looking for in each gear. I had to fabricate an aluminum box to hold the new ignition and charging system components, that mounted under the seat. Spark is strong. The only hitch I had was discovering there’s quite a bit of current running through the kill switch wire (who needs coffee?), and my original plan to use a micro-style switch didn’t work. Instead, I installed a toggle switch under the seat to act as a kill switch and to discourage theft.
Once everything was together, I was still having some issues with starting and running. I started the project in PA at 400’ above sea level, but was finishing it in NM at 6,400' above sea level. Instinct told me it was a fuel issue, running too rich. I’ve always been good at jetting and setup work, but I couldn’t get the Mikuni’s reliably right. A friend recommended trying a pair of 36mm SmartCarbs. After speaking with Corey Dyess at SmartCarb, I felt confident that these would allow me to ride all around this area, from 9,000’ down to 4,000’, without having to mess with the carbs. These should also provide a major improvement in gas mileage - important as it can be a long distance between gas stations here. These were NOT cheap carbs, but they are worth the price of admission. They’re built like a brick shithouse, beautifully made, and their tech support was fantastic. Setup was straighforward, just following the directions. I prefer mixing data and instinct when doing setup, so I installed a pair of bungs in the header pipes, installed an O2 sensor, and connected a fuel/air mixture meter. The meter was small, fitting right in between the gauges, and giving me great information about the mixture in real time, during test rides. Once I had the carbs running between 10.8:1 and 12.2:1 in all conditions, I did a plug check and had exactly what I wanted to see. Then I removed the fuel/air meter and wiring. I wish all cycles came standard with these meters, but that’s just me.
The only issue I have with the new carbs is that my Motion Pro throttle assembly can’t provide the travel needed to operate the slides from idle to full WOT. I’ll contact them to come up with a solution soon.
The bike now starts with one kick, cold or hot. I’m 65 yrs. old and I don’t kick like I used to, so this was important! It runs better than it ever has – stronger pull at all throttle positions, no issues on decel, crisp off-idle response and great WOT performance. I now have to be careful not to hit the throttle too early in a corner, as I can get into trouble quickly.
I hope this can help someone else avoid chasing their tail trying to get their bike running right. If you have any questions about parts, pieces, suppliers or installation details, I’m here to help. I'll add a couple of photos soon. Best of luck!
I’m hoping this post will help someone with their project. During the build I ran into several problems that should have been easy to solve but weren’t. Here’s what worked for me:
Bought my 1981 XS650 Special II brand new in 1980. In 40 years it’s never been dropped, always garage kept, and in pristine condition. I started the project in 2010 and finished this week - it hasn’t always been my first priority. I'd replaced the original Keihin’s with a pair of Mikuni flat-slides - a great upgrade at the time. All else (except wear items) was original. Total miles were about 24k. A friend mentioned Café Racer Magazine, and that the XS650 was a favorite for café builds. Add my love for the look (not the reliability) of old British bikes, and I had to take the plunge.
Rule #1 was that no part of the frame would be cut or welded. The bike was in such good condition I wanted to leave the door open to restore it to original spec. I saved all original parts. The final result would have been better looking if I’d removed the numerous mounting tabs, etc., but…
I stripped as much weight as I could, omitting the center stand, starter, battery, and fenders. I replaced the wheels with lighter rims and tires, the gas tank with an aluminum tank, the rear seat with an aluminum/fiberglass seat and cowl, the handlebars with aluminum clip-ons, the original pegs with a pair of aluminum rearsets, and a lightweight drilled front brake rotor. I replaced the original exhaust system with a 2-into-1 header and a new lightweight stainless steel muffler.
Step #1 was strip the bike down to nothing and powder-coat the frame. I should have masked the serial # first, as I found out when trying to get it registered. Rookie mistake.
The original engine had always pushed a lot more exhaust pressure out one pipe than the other, even though cylinder compression was closely matched and the carbs were synched precisely, so I decided as long as I had the engine out I’d rebuild it. I ported and polished the heads, installed new rings and pistons with stock sizes. I replaced the valve seals, and glass-beaded and lapped the valves. I replaced all crank, rod and camshaft bearings, etc. I’ve used Amsoil in the engine since it had 500 miles on it, so there was no wear on anything (except the cam chain guide, which had nearly disintegrated), but as long as I had it apart I figured I should do it all. I considered a 255 degree crank conversion or punching out the engine to a 750, but elected to keep it simple. I replaced all bearings, seals, gaskets, O-Rings, etc.
Regarding suspension and chassis, I replaced all bushings and bearings, installed Tommaselli adjustable aluminum clip-on handlebars (love these), and had TAB Classics make me a fantastically beautiful aluminum Manx-style gas tank with a flush cap and a single seat/rear cowl (these were so beautiful that I scrapped my original plan to paint this bike, and instead went with an aluminum/stainless steel/black color scheme). The tank has the factory-style front mounts, but I had to fabricate a mounting system for the rear of the tank, and I installed a pair of old-style Ducati petcocks w/ ¼” outlets. I fabricated a seat from a bottom layer of 2” moderate-density foam, a top layer of 2” memory foam, and I subbed out the leather seatcover locally. I fabricated various aluminum mounting plates for the new aluminum rearsets, the taillight, and the headlight angle-adjuster. I used Race-Tech parts and pieces to rebuild the front forks and replace the rear shocks. I changed the tire and wheel sizes, using a slightly larger diameter/slightly narrower width rear wheel than stock, and a slightly smaller diameter/slightly wider front wheel than stock. I lowered the rear shock slightly to adjust the rake angle of the suspension, increasing the positive caster to make the bike a bit more stable at higher speeds (highway speeds here in NM are 75mph, which has that 650 engine working hard. I’m not anxious to experience any tank-slappers at high speed).
The original electrical system (charging and ignition) was hammered after 30 years. For controls I went with Purpose Built Moto for micro-switches and lighting. I originally bought a Hugh’s Handbuilt full ignition/charging system, but it didn’t work. After 7 years of flat-rate wrenching and working on vehicles for 50 years, specializing in electrical systems, I had a good idea what to look for, but I couldn’t get it to go. Tried to get help (or any answer at all) from HHB with no luck. Since I’d waited 2 years before installing the system, it was out of warranty. Regardless, I’m done with HHB. I changed course and ordered a Vape ignition system from Dan at RE-MX. He answered all my questions, and his answers turned out to be dead-nuts accurate. The Vape is a fantastic ignition and charging system! I also got an ultra-lightweight lithium battery to power the LED headlight/turnsignals/brake light and horn. I tried the first and fourth options for setting the advance curve on the Vape, but the fourth was a bit too "smooth". I went with the first (original) setting which gave me the kind of kick in the ass I was looking for in each gear. I had to fabricate an aluminum box to hold the new ignition and charging system components, that mounted under the seat. Spark is strong. The only hitch I had was discovering there’s quite a bit of current running through the kill switch wire (who needs coffee?), and my original plan to use a micro-style switch didn’t work. Instead, I installed a toggle switch under the seat to act as a kill switch and to discourage theft.
Once everything was together, I was still having some issues with starting and running. I started the project in PA at 400’ above sea level, but was finishing it in NM at 6,400' above sea level. Instinct told me it was a fuel issue, running too rich. I’ve always been good at jetting and setup work, but I couldn’t get the Mikuni’s reliably right. A friend recommended trying a pair of 36mm SmartCarbs. After speaking with Corey Dyess at SmartCarb, I felt confident that these would allow me to ride all around this area, from 9,000’ down to 4,000’, without having to mess with the carbs. These should also provide a major improvement in gas mileage - important as it can be a long distance between gas stations here. These were NOT cheap carbs, but they are worth the price of admission. They’re built like a brick shithouse, beautifully made, and their tech support was fantastic. Setup was straighforward, just following the directions. I prefer mixing data and instinct when doing setup, so I installed a pair of bungs in the header pipes, installed an O2 sensor, and connected a fuel/air mixture meter. The meter was small, fitting right in between the gauges, and giving me great information about the mixture in real time, during test rides. Once I had the carbs running between 10.8:1 and 12.2:1 in all conditions, I did a plug check and had exactly what I wanted to see. Then I removed the fuel/air meter and wiring. I wish all cycles came standard with these meters, but that’s just me.
The only issue I have with the new carbs is that my Motion Pro throttle assembly can’t provide the travel needed to operate the slides from idle to full WOT. I’ll contact them to come up with a solution soon.
The bike now starts with one kick, cold or hot. I’m 65 yrs. old and I don’t kick like I used to, so this was important! It runs better than it ever has – stronger pull at all throttle positions, no issues on decel, crisp off-idle response and great WOT performance. I now have to be careful not to hit the throttle too early in a corner, as I can get into trouble quickly.
I hope this can help someone else avoid chasing their tail trying to get their bike running right. If you have any questions about parts, pieces, suppliers or installation details, I’m here to help. I'll add a couple of photos soon. Best of luck!
. Went on the smart carb website and had a peek at them. Love to have them but a pair would be worth more than my bike. lol. Great build and story. I think I see your bike in the 2026 Calendar. Congrats. I’m sure you’ll get the bugs worked out soon.
