Mutant Buell Donor Bike

Choosing the right donor bike

A lot of folks ask us what year and model Buells make the best donor bikes when they’re looking to build a Redneck Engineering Mutant Buell,  or any of the other aftermarket “donor” frames. So here’s a quick rundown of what separates good from great when it comes to buying a used Buell.

1. Carburetor vs. Fuel Injection: All Buell tube frame models from 1996 to 1998, as well as 1999-2002 M2 Cyclones were carbureted with standard module ignition systems, while 1999-2002 X1 Lightning and S3 Thunderbolt models came with factory fuel injection. Obviously, in a bare bones chopper or custom the bulk of extra wiring needed to run a fully integrated, closed-loop fuel injection is much more than most folks are looking to try and hide, and a majority of builders will lean toward switching the engine over to a carburetor. This a very simple swap, requiring the purchase of a new carburetor with appropriate fittings and brackets, an intake manifold, as well as an ignition module (either external box or nose cone modules will work in this case) and a new timing rotor cup. This extra investment should be taken into consideration when you’re budgeting your build if you choose one of these late model, fuel injected bikes.

2. Thunderstorm Engines: Buell debuted their “Thunderstorm” engine package in 1998 in the limited production S1W White Lightning. The potent combination of high flow cylinder heads, 10:1 compression ratio pistons, .497 lift cams, hotter ignition timing and a 6800 RPM rev limit was an instant hit, and gave H-D it’s first claimed 100+ horsepower production motorcycle. Of course this 102 horsepower claim was based on power at the crank, whereas most of these bikes averaged 85 ponies to the rear wheel after parasitic losses in the primary, transmission and final drive. Buell went full production with the Thunderstorm package in 1999-2002, with all three models, the X1, S3 and M2 featuring these parts standard. While the X1 and S3 share the same configuration as the original S1W, the M2 was fitted with the milder XL 1200 cams for a torque-heavy combination. If you’re looking for out of the box performance then it’s worth your time to shop around for a Thunderstorm-equipped bike, as the difference in power output is seat-of-the-pants apparent. Keep in mind too though that many other 1996-1998 models were upgraded to the Thunderstorm parts, as Buell offered the package as an all inclusive kit that many, many owners opted for. Easiest way to tell a real set of Thunderstorm heads is color, as every set of Thunderstorm heads has been powder coated solid black, while all the earlier factory Buell heads came in silver. Again, if you have any questions regarding what to look for in a motor get a hold of us at T.B.C., or if you’re looking for a way to make even more power give our friends over at NRHS V-Twin Performance a look online at or call them at 303-833-4500. These guys wrote the book on XL and Buell performance, rewriting the Bonneville record books in the process.

3. Inverted Tube Front Ends: All 1996-1998 S1 and S2 as well as 1999-2002 X1 and S3 models came standard with the Showa inverted tube front end, while all 1997-2003 M2 models rolled off the line with a conventional tube and slider fork assembly. This decision is purely one of personal taste and aesthetics, as either set-up is perfectly usable from a function standpoint. Some of course like the heavier, more modern look of the inverted tubes, while other will like the simplicity and classic lines of the standard forks. New inverted fork assemblies are still available from H-D/Buell dealers if you should decide to take and M2 based bike that direction, or if your donor was a wreck with fork damage, but plan on investing a grand by the time you get both tubes and a set of triple trees to match. Both front ends use the same axles as well as the same six-piston Nissen brake calipers, so everything is interchangeable.

4. Price differences: 1997-2002 M2 Cyclone models will generally bring the lowest prices in comparison to other Buells from the same model year, as they were the cheapest new model in each of six years they were built. S1 and S1W Lightnings will generally come next in line, with S1W’s commanding higher prices, based on their fledgling collector status. From there it runs to the 1999-2002 X1 Lightning and S3 Thunderbolt models. These bikes were Buell’s most expensive production models, and the used resale market reflects it. With enough patience and a little hunting around pretty much any Buell model can be had at a fire sale price, just pick the model that best fits your wants and needs and go from there. Some great places to search for used Buells include the bikes for sale classifieds at as well old standbys and

We look for bikes in this order - No.1 on our list has to be the 1998 S1W White Lightning. It’s got everything we like to incorporate into the mutant in one package: inverted front end, carburetor, standard ignition and the hot-rod Thunderstorm engine. It’s the perfect donor bike. Unfortunately, there aren’t tens of thousands of these things, as less than 5,000 of them were ever built, so finding one period can be difficult and because of their popularity sellers can command a premium price.
No.2 would be the 1999-2002 M2 Cyclone. Thunderstorm heads and pistons, carburetor, standard ignition and standard forks. Some great buys can be had on used Cyclones and depending on what your front end plans are, the standard tubes may be going on the shelf anyway. (Our black bike seen elsewhere on the site started life as a 1999 M2)
No.3 would be 1999-2002 X1 or S3 models. Even though these bikes can run a little higher up front, and can cost even more if you switch out to a carburetor, they still come with a lot of trick bits and are worth a look.

Hopefully this quick rundown on some key points will help you in your search for the perfect donor bike. Basically any tube frame Buell will work, but picking the year and model that gives you the majority of features you’re looking for can save you a lot of time, money and headaches in the long run. Again if you have any questions please give us a call at 970-587-5867 or drop me a line directly at