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/126770
1.88mm BTDC. The carburetor main jet must be changed from a #360 to a #260, and the needle jet must be changed from 6F15-2 to 6F53-4. Yamaha claims the power gain from installing the kit parts and making the required modifications is a modest 5% over stock. To get even more power, Yamaha recommends milling I mm off the base of the kit cylinder and using two head gaskets; as well as milling the head 0.015inch, while maintaining 0.030-inch squish clearance. There's more: paning changes to the kit cylinder are recommended, and the kit includes specifications and diagrams. Then, on top of the changes recommended in the kit di,,grams, two boost ports measuring 13mm tall by 7mm wide must be added to the cylinder. Remember the new pipe included in the kit? It has to be cut in half at the widest section; after removing 5mm from the middle, the two sections must be we.lded back together. When all the parts are modified and installed, the engine needs at least one-hour break-in time. We rode a modified, killed YZ and a stocker back-to-back and the difference is quite noticeable. The modified YZ's low-end was drastically sacrificed; it hit hard just where the stocker stopped pulling. On hardpacked, dry tracks, the transition from not much low-end to lots of power is too drastic: the back end shoots out to the side under hard acceleration; the power kick sometimes seemed to come on too late, just before the bike had to be braked for the next turn. That's no problem for a Pro or Expert; for others, it could be a handful. But for long straights, the YZ hooked up and went. We installed a 50-tooth rear sprocket, replacing the stock 48-tooth sprocket. Although the gearing change doesn't alter the powerband, it does make the YZ easier to ride because the transition between low end and mid range happens sooner, more predictable and is easier to keep in the powerband. Although the power comes on hard, it quickly mellows out, but 'not as severe as the stocker. Yamaha claims the YZ's overall performance is improved 10% after the modifications to the kit, which we feel is about right. But that 10% isn't enough to make the YZ runaway from it's competitors, though, but is enough to stay in the hunt. Is the hop up kit worth $366? Considering it as cost-to-performance value, it really isn't. However, in the right situations, the kit could be·a money saving investment. If your YZ is still stock, due for a new top end, and if you are considering buying a new pipe (if not, you should be), or having it ported, anyway, then the performance package is for you. After adding up the cost of all those parts and portmg, the kit would be half paid for, if not more. Taking the extra piston and ring set, and the chrome bore cylinder (which doesn't have to be bored) into consideration, the. kit could save you a few dollars and make the difference on the track. Yamaha also makes hop-up kits for the YZ250 and 490L for the serious motocrosser only - specifically the Pros. These kits require no modifications, but they cost more than the 125's. The 250cc kit retails for $398, and $487 for the 490. All the hop-up kits are ouly available through the Competition Support Department at Yamaha Motor Corporation, U.S.A., 6555 Katella Ave., Cypress, CA 90630. For more information contact Clark Jones, Communications Coordinator, 714/ 761'-7511:'"", . ,0.,_ •• ' WESTERN YOUTH REGIONALS (only) ••Illey ORV Pri 1Ie.IM_me, OR JULY I . . 503/472-2475 lndiano.... V.lnc~. CA . 213/868·8"2 JUNE 30 ".. .. Min,mum 4 per class each track advance WESTERN AMATEUR REGIONALS (only) ...Ikey ORV Pri .Mill,,'lill•• OR . ... 503/472-2475 JULY 1 ...............• •"dle. Du••s Valenci.-, CA JULY 1 , ...•................... 213/868-8112 Minimum 4 per class each track advance NATIONAL CHAMPIONSHIP TRACKS NO. CENTRAL AM & YTH AREA LOCATIONS MIDWAY REt. PARI Kellogg, MN CEDAR VALLFt Springville, 1,11, (311)313-_ M1DWAY MX Mitchell. IN OLASS CITY Me Della,OH AlNInr R,,1eftI1 C""",*,MJllp UMCOLH TRAil Casey,ll YOIItII Retloftll C• •I.....'" MOTOSPOfm PMK Byron.ll. (217)1S2-.1 (115) zst.2%71 SO. CENTRAL AM & YTH AREA LOCA TIONS COIHITR'" Mooreland, OK '...1-.... ME IWFF MX Pille Bluff. AR "AI" Tyler. TX COIdIOE illI)l "All (Amateur only) Conroe, TX (7131141.J125 .....r ......... ~ UlE WHfTJIf'f CYCU: IWICH ,--- fN31,"·~ RIO BRAVO (Yout!l Onty) ........ TX .. . . . . (713) 141-3125 lake Whitney. TX l.AIE ~ m:u IWICM lake Whilney. TX Youth and Amateur Qualifiers held at same locations on different dates SEND ENT"llS NOW - COMNTf '1IIISllIUCTlOtI P'ACUOE "fTU1UIEO ALIM PRE ENTRY DEADUNE POSTMARKED MAY 12 . ENTRY FEE 520 PER CLASS· POST ENTRIES $10 MORE AT TRACK SEND CHECIl 011 MOIIIEY ORDER TD: MX SPOIlTS. P.D. lOX .... TDLEDO, OHIO 43112 An additional $10.110 Ilgn·up per clllS Ind gill Idmlalon will bl c""rgld II thl rlCI trlckl. SANCTIONED $11,011O U.S. Boneb PRO-AM PURSE A.T NATIONAL nNA.L IlllfOAMAnON: (411) .n·5311 ENTRIES f (3CM) 514·1157 GENEUl ~-----------~-------------------------------------------------~ CHECK CLASS: You liliy I1IIor Z AIIII'-'r Inlllor Z YouIlllWOIIIfJIIISr. MeIJIPro.Am Cg_ II Aru & bul musl choo. only Z cia_III rlde,1 N,_ 111II/O""_, NAME FI"". 1. 0 l00cc TOWN ZIP BIRTH OATE rn CD CD MO AGE OESIRED QUALIfiER TRACK DAY ___ VR AMA N ITIIIIJ EXPIRES CAN BE PURCHASED AT TRACK BIKE BRAND NUMBER . PREfERENCE -"( AMATEUR TRACK rn YOUTH TRACK MO·YR ___ AMATEUR 6. 0 250 A Stock 2. 0 125 A Stock 7, 0250 A Mod. 3. 0 125 A Mod. 8. 0 250 B Stock 4. 0 125 B Stock 9. 0 250 B Mod. 5. 0 125 B Mod. 10. 0 Open A 11. 0 Open B Amlteur Expert Ride" ride A or Pro-Am. 1983 AMA & NMA NIttOtlll Ride" placing In top 10 018 or I . _ I t cloaa ride A or Pro-Am. Top 10 1110cc or 125cc (12·15) ride A orPro·AmltmmngtoAmlleur.DIherYouttl Ride" moving to AmIleurmlY rideB. Youth Mini (12·15) placing In top 10 mlY ride Mini, 125 A (12·15) or Amlleur B. YllUTHIWOMENISR.MEIIIPIIO-AM 12. 0 51ce Automatic (4·8) 13. 0 55cc Stock (7·11) 14. 0 65cc Mod. (7·11) 15. 0 B5cc Stock (7·11) 16. 0 B5cc Mod. (7·11) 17. 0 85cc Stock (12·13) 18. 0 85cc Mod. (12-13) 19. 0 85cc Stock (14-15) 20. 0 85cc Mod. (14·15) 21. 0 125cc A (12·15) 22.0 125ccB(12·15) 23.0 Women (86cc·125cc) 24. 0 SR _30 VR (101cc.Qpen) 25. 0 PRO.AM (101cc.Open) Hi-Point & Ashcraft Win Nat!. H.S. Hi-Point-equipped DAN ASHCRAFT battled over 300 riders and the Lucerne Valley, CA desert to win the fourth round in the AMA/Hi-Point National Hare Scrambles Championship. NEW! 1984 Hi·Point Pro Boots Available NOWl See your Hi-point dealer for mens' sizes 5 through 14 in Red, Blue or Black. Hi-Point Mini MX Boots available in youth sizes 1 through 7 in Red. Blue or Black. Winner. like DAN ASHCRAFT rely on the •• me HI-Point Reclng equipment thet you cen buy from your d••I.r. Go ... Him Tod.yl '" 2-6..