Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/127848
PROJECT BIKE Tom Morgan Racing 1997 Yamaha YZ125 By Cameron Coatney Photos by Matt Freeman and Coatney ha t do yo u get when you take the b est 125cc m otocrosser of th e yea r wait , make that the best motocrosser of the year, period - and let Tom Morga n Racing give it his complete high- perform an ce ove r ha u l? You ge t o ne mean machine that will grea tly improve your cha nces of ge tting out of the first tu rn first, and keep yo u ou t front for the rest of the race. Some of you yo unger racers and rid ers ma y no t exactly kn o w w ho Tom Morgan is, but those of you readers w ho have been in to the motocross scene for the past 10 or 15 years pr ob ably know exactly who Tom Morg an is - and why w e w ould trust him to make o u r YZ even better than it already wa s. For th ose o f yo u not in th e kn ow , here's a little background : Morgan started at Kawasaki as a model tes ter and designer in 19HU, an d switched over to becom e Billy Liles' factory mechanic in 1983 . Af te r a few Na tio na l MX wi n s wit h Liles, Morgan beca me Eddie Warren' s mechan ic in 1986. After a few more Na tional wi ns wit h Warren , Mo rga n was positioned as jeff Ward 's mechanic, an d the pa ir went on to fou r Natio nal Cha mpio nships toge ther. In 1993, Morgan beca me Mike Lakocco's mechani c, and the two pr oceed ed to win the 500cc National Championship that seaso n (the last yea r the 500cc Nationa ls were run). In 1994, Morgan started Tom Morga n Racing , b u t wa s h ir ed b y Kawa sak i again to develop race moto rs for th eir facto ry wa tercra ft racing team and also to se rve as Victor Sheldon 's mechanic. Sheldon went on to win the Pro Runabout 785cc N ational Championship. Morgan al so built Mike Craig's a n d john Dowd ' s mo tors when they rode Team Green-backed Kawasakis in 1993. ". . o. I' 34 (Above) The Tom Morgan Racing 1997 Yamaha VZ125. These da ys, Morgan devotes his time to testin g and d eveloping com prehensive motor and suspension packages for all four of the japanese brands under the Tom Morgan Racing (TM R) banner. Nationa l MX regulars Heath Voss (]25 and 250cc) and Ryan Huffman (250cc) currently run his motor mods (Voss also runs his su spension mods), and Huffman wo n th e coveted C.E. Altman Award for being the top finishi ng privateer in the 1997 AMA 250cc Supercro ss Series . Morgan also does a slew of top Amateu r' s bikes, a nd just recently s ta r ted do ing the mo to rs of one of the factory rid ers (who sha ll re main nameless, for obvious reasons), After years of being a fact ory me chanic, tuner and des igne r, Morgan kn ows how to tes t and find . what works. In other words, Mo rgan know s exactly what he's doing - and he sure di d il to ou r YZ125. In stock form , Morgan felt the YZI25 engine had good overall pow er with a broad, easy- to-use po werband. So wha t he was o ut to produce wa s more peak power, stronger accelera tion, an d better thro ttle response at all rpm, but without losin g the friend ly, easy-to -use nature of the stock powerplant. In an effort to achieve these goa Is, Mo r g a n modified and p orted o u r cylinde r and extensi ve ly worked on the head to produce the best combusti on-ch amber s ha pe. A modifi ed Wiseco Pro-Lite fla t-top pist on is used , and requ ires the use of a 3mm s pac~r washer between th e s par k plug (NGK B9EV) and head. TMR d oesn 't make exhaust sy stems but rat her relies on testing and u sing pipes from the top pipe manu factu rers in the country - like Pro Circuit, FMF and Bill's Pipes - for his selection of expansi on chambers (jus t as a few of the facto ry teams dol. For the YZ125 and his mod s, Morgan recommend ed a Pro Circuit Works Pipe and Factory Sound Silencer fo r best overa ll power, so we had to have them. Morgan then ex tensi vely modified the stock reed cage to balance the intake flow between th e left- and right-side . cy linder po rts , and used carb on-fiber reeds of his own design to reduce intake turbu lence at high rpm and prod uc e clean ovcrrev. The stuck carburetor (36mm Keihin ) is bored 1.2mm and jetted accordingly. Morgan also trued and lightened the flywheel; and recommended runnin g a higher-pressu re rad iator cap (23 psi vs. 15 psi stock) to virtua lly elim ina te any chance of boil-over in warm conditions. Th roug h ex tens ive testing, Mo rgan claims he has seen a 4O-