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/125848
a • This Jim Pomeroy Americanized Replica will totally change Open class racing. By Jim Gianatisis Photos by Charles Morey. Gary Van Voorhis and Gianatisis Past ideas and designs are being left be h i n d rapidly. The technology of motocross machinery will be as radically , d ifferent in 1974 as it had been in 1973 . El si n o r es , re e d valves. monoshock Yamahas and other inovative designs are already co m m o np lac e a nd will have to give way to even newer ideas. The 1974 Bultaco 360 Pursang is such a new idea. This past fall when we tested the Hus qvama 360 Grand Prix bike which Heikki Mikkola will be racing in the World Cha mpionship rounds t h is yea r . we could hard ly believe th at the bike was so tractable and easy to ride. Broad , smooth power fr om idle almost , right up the rpm range to about 7.g ,000 . Bultaco's new 360 follows very much this same idea of usable power, but takes it one step further . 20 It is common knowledge th at o n most motocross courses, even mor e so in Europe where the courses are rough and difficult, a 250cc bike can get around a track much quicker than a comparable Ope n class mach ine. They're lighter and easier to handle with better engine response. What Bultaco has done in effect, is build a 250cc ra cing bike for Open class competition that has an actual displacement of 352 cc. This just meets the FIM's minim um displacement limi t of 351cc for Open clas s engines. Instead of using that extra 102 cc left over to get more ho rsepow er fo r their 'cheater 250', Bultaco uses the ext ra displacemcn t to increase power at low er rpms by employing th e larger port are a that is available with much less rad ical port timing. All this seem s ver y un -Bu ltaco like. Th e first time we rode th e 360 it left us finge ring o ur low er lip s and wondering if th e factory didn ' t put a Sh erpa T cylinder on it by mist ake . It wo uld n't rev past 6,000 rpm and the pow erban d had already dis appeared at five . All the old phrases ab o u t underp owered bikes came to mind as we tried to figure out if the bike was rea lly in tu ne o r not. It was . And th e mo re we rode t he 360 the more we began to understand it. Th e engine is a puller and no t a revver.To go fast the engine has to be all owed to pull fro m very low rpm's and shifted early. Power to the ground over a very broad powerband is where the 360 Pursang is at . _ Besides the change in di splacement o ver the old 325 Pursang and the porting differences , the new 360 has a stronger crankshaft that is wider and hea vier t o s moothen . the power impulses. Externally the engine looks the same except that now a Motoplat ignition fires two s p a r k plugs simultaneously to provide a much more needed low speed spark. A 36mm S p an i sh A mal still handles the carburetion chores, and while it wo rked satisfactorily an d was jetted properly, it usu ally took fro m five to ten kicks to get the engine started when it was cold or had been sitting a few minutes. We just don't get along with tickler buttons fo r flooding an engine to get it started . Throttle response also seemed a little slugg ish thro ughout the operating range of the engine . A 34 o r 36mm Mikuni carb would probab ly so lve our o nly minor complaint with the engine. Now that Bultaco had th e ' ult imate' 250 engine in th e 360 , the ne xt thing to do would be to put that engine in a goo d handling 250 fram e. Sin ce Bultaco w a s a l re a dy d o in g th at , the 1 2 5 /2 50 / 32 5 Pursan gs had alw ays sha red th e sam e chassis, t he o nly thing required would be to ligh ten it up a little. And ligh ten it up for 19 74 the y did . Ch ro me mo ly steel wa s use d to replace the mild stee l in the fra me, swi ng arm. an d hand lebars. A new lig h t we ig ht t u rn ed rear hub wit h chrome p lated brake drum en aluminum