Below are the most common motorcycles to build and modify into a cafe racer or Brat Style bobber.
Suzuki GN-400 GS-250 GS-400 GS-450 and Suzuki GR-650 Tempter. In fact the GR-650 is a darn good one, but hard to find. Make sure to check out the dual sport thumpers like the SP-370 SP-400 DR-400 DR-500 and DR-600. I always had a love for the big twins. They are my favorite off road trail dirt bikes. A scrambler or desert sled has so much comfort compared to singles. The Kawasaki W650 and Yamaha XS 650 come to mind. A good scrambler project would be the the lighter XS 400 KZ 400 or Suzuki GS 400. Even the Honda CB 750 makes a nice desert sled, as the CB 750 can be stripped down to about 400 pounds. Choose the older SOHC version of the CB 750. Of course the most famous desert sled of all time is the Triumph 650 T120 and Triumph 750 T140 models. However the Honda CL 450 Scrambler has about the same amout of horsepower. If you want a real thumper, check out the Suzuki Savage S40 650. You can swap out the Savage 650 belt drive for the chain and sprockets from the GS-550 models. P99 XDm Best 9mm Pistols Affordable Chevy Engines
Something else I have learned is that a street-tracker with knobby or trials tires makes a better off road scrambler enduro that a 500 pound adventure dual prupose bike. I am not kidding!
Now to the Kawasaki KZ series. During the 1970s and 1980s, Kawasaki made some of the most reliable motorcycles you could buy. The vintage Kawasaki KZ-400, and KZ-440 are awesome to build. I had a KZ-400 with a 19 inch wheel from a CL-450, vintage Firestone tires, and GPS speedometer. It was a brat style street fighter and so cool. The classic KZ-305 is a small bore speed deamon, and of course there is the KZ-750 Twin cylinder. The KZ-550 is also very light for a 4 cylinder.
The Honda CB-350, CB360 CL360 CJ350 CM400 CM450 and CL-350 are easy to find, but a little underpowered. Mostly because you are only getting 326cc of engine from the 350. The CB-450 and CB-500T are popular. Hardtail frame kit The Honda CB-360 and CB-400 twins are some of the most sought after. The CM-400 and CM-450 are cool, and with the Hondamatic transmission is even cooler. The Honda CRF-450 and CRF-250 can be made street legal. Hardtail struts The older SOHC Honda CB-750 is even light enough to make a decent cafe racer or Brat Style bobber. Others: FT-500 Ascot, VT-500 twin scrambler, XL-350 thumper, and the XL-500 enduro. If you already have a twin shock frame, the XR-600 and XR-650 air cooled engines make good power. The CB-550 bikes from the late 1970s weighed only about 400 pounds before you gutted them. More YZ250 Horsepower Increase HP
We already talked about the Yamaha XS-650. Other nice ones are the XS-360 and XS-400. I owned a Yamaha XS-400 that was reliable as an anvil. Avoid the TX-750 and XS-500 as both can be trouble. The YZ-450F and YZ-250F you can add lights. The thumper single cylinder Yamaha XT-500, XT-550, and XT-600 make good cafe racers. MZ imported some bikes that had the Yamaha 660 single in it. However finding a MZ 660 may be difficult. The Yamaha SR-500 single is a top prize too. The SR-500 may be the best road thumper ever made.
European motorcycles to consider: The 1997 and later Triumph 795 T100 and 865 Bonneville are good to build a nice desert sled. The triumph Scrambler would be awesome because of the 270 degree crank. Royal Enfield 500 is half way there. The Ducati 620 Monster and 695 696 Ducati monster found used will work. In fact the older 750 and 900 Monster are sweet. Just get taller handlebars. The newer Moto Guzzi V7 750 is very light weight for the size. An used Moto Guzzi Breva 750 can be found at bargain prices. Go American: Look for a Harley Davidson Sportster basket case. You can build a Harley XR-750 style street-tracker out of a Sportster 883 or XLCH 1200 too. The Buell Blast 500 can be found cheap too. In fact the Buell XB9R and XB12R work great.
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