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/126009
*( Try if in ;our) 'frannie' fooll ./ Consumers agree •••• "it really works" HRLINC. 2600E.Nutwood Ave. I !'!J.'!.':!.~.s~ !U!1._.I new Chain Tensloner E.C:s complete "works mini racer" including the moved-up shock conversion detailed earlier in Part I. Extr a hea vy duty tensione r - p recision manufactured with Tefl on rolle rs to resist wea r under ex t reme use . Dual function: spring loaded roller keeps chain taut and the angle of the mount acts 8 $ a chain gu~e and prevents mud or brush from getting into the rear sprocket. Heavier duty w ith close r Part II..Tricking the engine to lerances and higher lest springs than others on the market. By E. C. Birt . $21.95 Cf~ For info contact: 8423 Rosemead Blvd. Pico Rivera , CA 90660 213-869-7346 Deal" &1 Dist. inquiri"s inuited Discounts to 40 % on genuine Yamah a parts Contact us to save on all Yarnaha parts. ------. . --........ ............................... --...--...----.--.... .... ------..... , . . . . _ • . . - _......... fOf _ _ _. 0.. _ _ ".3 __" --~----~ _ ~ .......... _ 16 -. ~ . . . . . . . . . . .I I I l I _ . _ ~ _ ..- With racing as it is today there are three 'classes that the Mini YZ 80 can race In depending on where you live. Two engines can be built from the 73ee cylinder; 83ee and 8G ee. If you're running in these I cl th arger. asses en. yo';! may want to build your engIne In to one of the bigger cylinder sizes and not give away the extra cc. First, we will look at the 73cc cylinder and the porting and trick stuff that will make it do its thing. The porting and p ip e specs will also work for the 83cc and 86cc engine sizes . Two things that y o u can do to that b o x st ocker that will give you a noticeable increase is air filter and a pipe mod. The air filter for the YZ 80 has a hurt, bu t th is problem is well handled by a filter fro m Fun &1 Fast . Any local Yam ah a dealer should have this filter in stock. Nex t, pull the pipe off and break out you r hac ksaw. Saw into th e pipe right wh ere the rear co ne starts. After you have the pipe apart dig out all the screen wire and fac tory carbon catc hers in t h e r e . After you have the in sides cleaned o u t like a catfish re ady for the fryin g p an , remove one inch of th e center sectio n and weld the pipe -bac k tog~ther Next . cu t of.f the. stinger . l~aVlng only ~>ne inch of it and install a sj le n ce r wi th a three -quarter or seven-eighth co re size , depending on the type of track th at you are racing on. Next step up the HP ladder is the reed assembly and the ca rbo The best reed for the engine , one used by most of the mini tuners, is the 0 .11. reed. Again this is a part that you can get at any local raci ng shop. The reed is a bolt on reed but you will have to do a li t tle rub~in!! on the cyl~nder reed housi~g.to get .t. m , (Note pi ctures for machining and bigger reed.] The D. H. reed is twice the size of the stock reed and the baby has to be red befo re it can grow. With th e ree d change, the s tock flange mo unt 22 mm carb is a little small. Get a I OOcc Yama ha MX m anifold (Part No. 304- 13565-70) wh ich will bolt to the reed and t hen you can choose anyone of three rubber flange mount carbs in either 24mm , 26mm, or 28mm, size. On most of the engines th at I build the 26mm carb is the one that we find to handle just about every need. Sudco In terna tional , 1824 Eas t .2 2nd Sveet, Los Angeles, California is th e h om e of Mik uni and they can build any of these carbs with the , righ t je t ting for yo ur engine needs. Now is the time fo r you to m ake th e ch oice if you're going to buy a com plete top en d engine kit or do your own. The p o r tin g diagrams are fro m Yamaha International racing department which is WFO so if you think you're not ready for that much lo ss to the bottom end torque then only go half of the amount to be removed. The pipe (Fig. 2) is just a li tde on the hard side to build but it works pre tty , good. Here you can also take the easy way out and buy the factory pipe for the 80 from your local Yamaha dealer. The 80 has what you would call a wide ratio gearbox and if you 're going to build your engine on the pipey side get a Noguchi close ratio gear set. It 's welt worth th e expense and the trouble to split the cases to install the set of close ratio gears . Now if you want to realty put so me hair in t hat little Yellow Zenker, then your next step is to go to a larger engine size . A 50mm bore wi lt give you 83cc p lus a touch . Wit h .04 0 (about I mm m ore ) you hav e 86cc which will make yo u legal to run in th e 100cc class. Wiseco has pistons th at will take yo u up to th e 8 0cc plus class or yo u can use a number of pistons th a t are ma de fo r other bikes like Suzuki, Kawasaki or Hodaka. If y o u happen to have a Noguchi cy linder that has go t its sel f in trouble then you can use it. After yo u have the welding and machining done to get the 'iY,lil',d,er .tI]e ,righ ! .h.ei gll,t ,Y,o u. f \'" bpre