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/125877
rn th at 178 pound bi ke. throw in a tank o f gas and yo u have a 190 po und rocke ts hip. If yo u take th e li tt le CR 125 and tune it j ust t he way it comes fro m the crate, you will come up with a good , solid 17. 5 to 18.5 ho rsep o wer to the rear wheel. Ever since this litt le fire breather came out on th e marke t I've been working to find those little hidden ponies that are there. With an engine like this yo u d o n' t do anyt hing ras h or you wind up going slower than if you left it stoc k, 1 don't, and won't make horsepower statements witho ut being able to back them up with a dyno chart. :~ • .... IlQ g ;... g ~ rC'l r:-. Reed valves . U ..0 E - u ..... 0.. u C/) E.C. Birr's Test Bench brings Cyde News readers the hot scoop on what it takes to make their machinery more competitive in the rough world of racing. Here's how it works : A manufacturer of a go-fast goodie sends a sample to E..C. (E .C.'s Test Bench, 509 Industrial Avenue, Boynton Beach, Florida 33435) for testing. The product is given a complete going over both on the dyno and on the track. If it performs, E.C. tells the world . If it doesn't, E.C. gives the manufacturer an o ppo rt un it y to see wh y not and to correct any problems, then reports on the results. You always get faster with E.C. Birt. Making Eisinores better Elsie at 178 pounds is the trimest little sweetheat you could ever want, because for a 125cc motucrosser, she's righ t on the weigh t button. About a year and a half ago, Brian Fabre, who was wit h the all migh t y. Dirt Bike, stopped by t he shop with a very impressive lo o king 125cc racer. It said Honda on the side of the tank. This was o ne of the first CR 125s to hit the states, and it was very top secret. Brian. rubbing hi s hands together, said with a gleam in h is eye "E.C . let's unload it and take a check on the engine to see what makes it tick for a te ch article. After the port timing layout sheet was finished. we looked t o see what the powers of Honda had given us . After studying the layout sheet for abo u t 10 minutes; we both kicked back and just shook our heads. Brian said. "What can you do to get more horsepower out of it ?" Well, it was plain to see that Honda had not only been wo rking late n ight hours, b ut Sundays as well . The on ly way I could answe r him was to p ut it ba ck toget her just as it was and think on it for about a week , because it wo uld win just the way it was. A year ago it was by far the most superior 125cc racer on th e market. Today. a year later. it is still the best buy o n the market for a stock box 12Sec rnotocrosser. You c an only get so much horsepower out of 71'z cubi c inches. Right now the pe ak is about three to three-and-a-half horsepower per cubic inch on gas. Put this kind of ponies in Is a reed valve the answer on the Banda? Well, if yo ur name is Marty Smith, no! J ust turn it up to 11,000 and leave it there like he does and very few people are going to pass you. Lyle D uto it, owner o f J & BRacing in Glendale, Arizona, has one of t he biggest Ho nda Racing Teams in t he United States. T he blue pain ted J & B racers have stacked u p a tr em end ous score of win s allo ver the Uni ted States . About two weeks ago we shared a can of Coors over a t o ol box a n d decided t hat all t he Honda rid ers wer e n 't Mar ty Smiths. With th is th o ugh t in mind we have worked to see wha t we can do for t hose of you who are n 't Marty Smiths but would li ke to be so meday. Let's ass u me that for the moment that you are a beginner rider a nd you have fou nd tha t yo u blow all yo ur buddies in the weeds in a drag race, but when you get on that rough m o t o cro ss track on Sunday you find yourself finishing in the m iddl e o f the pack. More horsepower probably is not what you need, but rather an easier bike to ride . In short, more torque is needed. A reed valve conversion will do this for your bike. Also, if Pop has been stealing your racer to go trail riding with ' his buddies he will love it. The reed will make your bike lose that pipy feelin g it has now by shoving in a bucket of torque in the m id range. There will also be a n in crease of horsepower on the top for a bonus. There's one ca tch he re; the reed assembly for the Honda is not just a bolt on trick like it is on some of the other bikes. The intake track is too small and when you grind out the inside of the intake for the reed you wind up with the daylight o n th e o u t side shining in . There ' are two ways o f so lving this problem. The firs t is th e easy way o ut (a little o n the Mic ke y Mouse side), to epoxy th e sides up. I' ve had ba d experiences with epoxies in t he past. If you do use epoxy watch it close for air lea ks. because if you get an air leak you're go ing to wind up with a one piece top end. There's on ly one way to do it right; Heliarc weld up the side of the inta ke where it's goi ng to break through behind the flange, and also around the gasket surface so the reed will have more surface to seat on . Use an end mill to r esurface t he gasket sur fac e so that it 's prefectiy fla t. Also be su re and ' check th e base of th e cylinde r because it may warp a little from th e welding and may have to be t urned for prope r sea ling. Photo A shows the area in black th at needs to be ground out for t he reed an d the arrows pain t to the place where you need to weld the cylinder. Diagram One shows two styles of bo ost ports. Photo B shows the boost port in the cylinder when using the stock piston. As you can see th is has two ports from the intake side leading in t o t he single opening in the cylinder. Figure One in Diagram O ne is the single boost port to be used with t he stock piston. Figure Two in Diag ram One shows boosts whic h require moving the ring pins or using the E.C. forged rac ing pisto n. Forged pistons The Honda engine has shown that as the horsepower goes up. piston life goes down, like a piston every race o r so in • some of the raci n g eng ines t ha t really pu m p o ut the pon ies. Si x m o n t hs ago I started wor kin g o n a d y ke rin g piston for the 12 5c c Hondas an d 125cc Su z, It is designed to accep t th e reed ports, third port, o r to be used as a regu lar re placeme nt p isto n for th e rider who wants to hea d o ff pi ston prob lems an d pick up th e extra hor sepo wer the dy ke rin g will give . T hese forged racing pistons ha ve been built to my specifications an d use a Popp y unbreakable ring. Race testi ng shows that they will last th ree to fo ur tim es longer than a stock pis to n . Pis to n sizes are as follows: Standard, 56 .0762mm; first ove r, 57.0mm; second o ver 57.5. Diagra m 1 Fig. 2 Boost ports E.C. piston or move ring pins Fig. 1 stock piston Diagram 2 3rd port t 1.550 .500 --..., Reed po rts 4- Diagram 3 .3rd port .10 0 Boo st port L .5 00 t ..., ~ rL ....J ~ ~ I-- ~ ( ---+ .5 00 ~OO t soa 28 /" .l i ...., ) .2 2 5 - i ,..