21st Century Tuning for Vintage MX 2-Cycles


There is no such thing as the “average” vintage 2-cycle bike … or rider.  With that we have categories that cover “most” riders.  Knowing the category of rider you are helps to choose the right modifications to best suit your riding (and budget) needs.  Here is that list :



“Reliability” Rider  – This is the most common kind of owner.  The biggest priorities are wide powerband, excellent “like stock” reliability, easy starting, and usually 91-octane pump gas.  This rider is less concerned with keeping up with the new bikes, and more concerned about not excessively abusing the perishable parts of his vintage machine.

Reliability Racer-  This racer enjoys the opportunity to run a vintage machine in a race, but is more concerned about having a good time rather than winning.  He wants a 91-octane machine with a wide powerband, easy starting, and excellent long term reliability. This rider would rather choose a more subdued pace rather than an intense pace that can be abusive to perishable parts of his machine.

Competitive Rider -  This non-racing rider is fit and skilled, and wants a fast machine to match his skills.  While reliability is still important, he is willing to deal with a powerband that is a bit more “aggressive” than stock.  This category can generally be set up for 91-octane fuel.

Competitive Racer -  This fit and skilled racer rides to win, and going “easy” on the bike is not a top priority.  He wants an aggressive powerband that delivers well at all RPMs.  This rider needs to expect to do regular maintenance and inspection work on all aspects of the bike.  While this rider does not need to use 100% race gas … a 50% ratio of race gas is a very good idea.

Elite Racer -  This is a top-level pro or very aggressive racer that runs the bike as hard as it can be run.  This rider makes no effort to “go easy” on the bike, and demands everything it can offer most of the time.  This rider is okay with a high rpm oriented motor that requires plenty of shifting and clutching.  This bike should always be run on “at least” 50% race gas.

Trials -  While Trials is by no means high stress competition that has engine reliability concerns, it does have some specialized needs.  Most important are, very clean and responsive carburetion that offers instant throttle response.  Obviously, there is also a need for strong low-end power, but along with that, a “linear” powerband with no big “hits” works best.


What is the Difference Between Tuning Today, and Tuning “Way Back When”


The building and tuning of vintage two strokes requires a whole different mindset (and priority set) than what has been used in the past … and here is why.


  During the 1970s & 80s, the primary focus of most engine mods for off road 2-strokes was to get the maximum possible power that could finish a day’s racing.  During the 1970’s, 98 octane “premium” fuel was widely available, and during the 1980’s, 93-95 octane was also available …. without the numerous additives that we see in today’s “pump” gas (ethanol, oxygenates, etc).


  During those same 70s-80s years, off-road race machinery was ridden by fit and younger (than us) riders that were ready to “flog” their race bike to the very limits of mechanical abilities at every outing.  Few racers worried about failing a mechanical part, because the supply of replacement parts was plentiful … and relatively inexpensive.


  Fast forward to 2010+.   Riding and racing “easy to maintain” vintage two-strokes is still great fun.  However the pump gasolines available today are of much poorer quality … and the supply of affordable (internal moving) replacement parts are in much smaller quantity.  The result is, the way enthusiasts ride their vintage two strokes is changed … and the way the engines are tuned also needs to be changed.


  The new 21st Century  “tuning fashions” have become two-fold.

A)    Make the widest possible powerband that has “acceptable” top end power” …. and

B)    Make the greatest-possible “reliable” horsepower that can be had “with the engine maintenance and fuel octane I can afford”.   Neither of these two priorities existed for competitive MX riders of the 70s-80s, and so, no race shops of the day did development work towards those ends.


About Perishability

  Our technicians “are” the same guys who built all the Team DG Honda CR125 race team motors for riders like Broc Glover, Gary Denton, and numerous other pro racers of the day.  The Team DG Honda 125s were very high rpm, “narrow powerband” platforms that required constant abuse to the clutch and gearbox.  At the DG race shop, it was common for all the riders to bring their engines in on Monday for routine replacement of any crank that had more than 4-5 races on it, and any gears and shift forks that were delivering missed shifts.  At DG we had shelves packed with all new OEM cranks, transmission gears, shift forks, clutch plates, and single ring pistons needed to repair that weeks fleet of engines.

  Those shelves of 1975 CR125 parts do not exist for anyone anymore, and so, there is questionable wisdom for anyone (who actually races) to build a race bike with that same “perishability.

  All of that said, a very fast and reliable vintage two stroke can still be built today.  However that build up has to be done with intelligent choices that allow the engine to be operated less abusively (ie with a wider powerband), and the use of more affordable and more readily available internal moving parts.

A Different Approach

  The technicians at Klemm Vintage helped to create the cutting edge tuning specs for a great many of the off-road 2-stroke competition machines of the 70s & 80s.   However in the 1990-2010 era, we specialized in developing high performance 2-stroke PWC engines that had to make the widest possible power-bands (to accommodate a “no-gearbox” PWC driveline), as well as developing the highest possible performance that could be had on today’s 91-octane premium pump fuels.


    While air cooled vintage off-road 2-stroke engines are obviously different in many ways from more modern 2-stroke PWC engines … The technical rules that apply to reliability, wide power-band, and detonation resistance, are the same.  For our PWC development work, we used data gathering instruments and modifications that didn’t exist in the 70s/80’s.   With these tools, we developed the most popular line of reliable 91-octane safe PWC racing engine packages.  We believe that the combined experience of having mastered both the 70s MX, and 90's, PWC genres, we have unmatched expertise that allows us to produce the most reliable and effective vintage off-road two-stroke engines.



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