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/126286
AMA continues carb restrlctor plate testing 0') M ~ ,.0 8 By Gary Van Voorhis ~ > o The AMA, iii a move to reduce spe ed and increase rider safety, will require car buretor rest rictor plates on all 750cc road race machinery. The restrictor will be a washer-like metal object fitted between th e carb and piston. Testing has been done Z with both 25 and 23mm orifices (o penings) . A decision on size has not been rea ched altho ugh 23mm test resu lts were the most positive. To be lega l nex t season a rider need only purchase th e inexpensive restricto rs a nd change jetting. Rid ers may expect a power loss of approximately 10%. The restrictor is the work of the AMA professional racing ' board . T he board too k under advisement many ideas on cont ro lling horsepower. Most. including engine configuratio n changes a nd fuel consumption limita tions. were considered an d rejected . T he rejections were based on economic. technical and p ra ctica l reasons of ad a pta tion . A three phase progra m of in vestigation of the restriction of intake a ir was set up. Phase on e involved flow bench test ing . Ph ase two incorpora ted dynomometer test ing to determine the size or ifice need ed to produce a 10 % redu ction in po wer . Pha se on e and two testing determined that a 25 m m orifice would produce the desi red results fro m a Ya ma ha T Z750D eng ine . Actual race track test ing by Kenny Rob erts at Riversid e. Ca lifornia for phase t hr ee confirmed the above observa tio ns. Robert s registe red an a P: proxima te two second red uct ion in la p times usin g the restricror p late. However. further tes ting at Da yto n a by Rob erts , Gary Nixon and Dal e Sin gleton did not b ri ng about the sa me results. A 23m m restrictor was then tested with excellent results. "T he 23mm . restricror tested at Dayto na provided us with some very positive results ," said the AMA's Bill Boyce . " Alt houg h lap times wer e only slowed by two to three seconds. 1 bel ieve tha t to p speed was slowed by nea rly 30 mph . Eac h rider concurred that th e bike was easier to ride a nd th at power cha ra cteristics exit ing corners reduced wheelspi n significant ly. That, I feel, accou nts for the minor reduction in lap tim es. Probably th e most im po rta nt p roduct of th e ' rest rict ors was th at the ir use lowered tire temperatures con side ra~ !y a nd th at increases the safety facto r. Although no track testing was done with th e three cylinder ' Kawasaki , phase on e and two testing have proven restrictors will have th e same effect on Kaw asaki 's 750 . "Thi s is not a means of equalizing competition," emphasized Bill Boyce of the AMA . " It is a means by which we can place eq u a l restriction on all machinery. Our testing h as shown that it will work." • going to J . ~. . -. ' ~{ J:.' -",' All fo r only . _,-a' ._. -; :' :' ':;,~:~ All the answers in the most complete Baja tour book ever! 12 detailed, large reference map s In color h ighlight. Veh icles for various road conditions d iscussed in the "About the Wheels You Drive" section. Over 100 full -color and black and whi te photographs . And much more! ~ , ~--------~------------Enclose check . : or money order to Name I CYCLE NEWS I PRODUCTS Address I ~ P .O. Box 498 Long Beach. Ca. 90801 City State Z ip 3