Yamaha Yz125g
YAMAHA YZ125G
CYCLE WORLD TEST
A Winner That Doesn't Need Modification
Trying to be competitive on a stock 125 motocrosser has in the past been almost impossible. Suspensions and motors needed reworking for pro racing and sometimes even club events. Our 1979 YZ125F was the least competitive in our 125MX shootout (June, 1979). But don't judge the 1980 YZ125G by last year's bike. The G is totally new. And it's jumped from the bottom of the heap to the top in one model year.
The most obvious change is the engine. The magnesium cases are shrunk wrapped small enough to look right for an 80cc. The countershaft sprocket is rear-set and on the right side of the bike, just the opposite of past YZ’s. A six-speed transmission is still used and the overall ratios are almost identical to the’79.The clutch, also moved, is on the left side of the engine. It is housed in an aluminum cage that’s connected to a helical-cut primary gear. Primary kick starting is standard and the CDI ignition ensures first kick starts every time. Other visible changes are cylinder head finning and cylinder shape. Both look much like last year’s works bikes. Carburetion is the same with a 32mm Mikuni feeding fuel through a six-petal reed mounted between the carb and the cylinder. Incoming fuel gets a head start through the arched intake skirt of the two ring piston. The cylinder bore is steel so overbores are possible in case of wear or
mishap. The cylinder, like most 125s, has enough port area to look like half-eaten swiss cheese, which naturally means the cylinder will wear quickly and that means the borable steel liner will be much appreciated.
The G has a new chrome-moly steel frame to go along with its other new parts. It’s a single downtube design with a single tube backbone. Gone is the tunnel. Like the larger YZs, the backbone dives from the heavily gusseted steering head to a point just above the carburetor and terminates. Smaller diameter tubes start at this point, one set forming the seat rails, the other looping down and curving under the engine then ending at the bottom of the large single front downtube. Another set of tubes ties the seat rails to the area behind the swing arm pivot, completing triangulation under the seat. The G has a nicely built aluminum swing arm with good triangulation and good plastic guards to prevent drive chain damage.
Suspension on the YZG is also new. Travel has been increased 2 in. at both ends and adjustability of the monoshock has been simplified. By placing the aluminum bodied monoshock unit farther back on the frame and turning the shock body around, spring preload and damping adjustments are moved from under the tank to just in front of the shock attachment point on the top of the swing arm. Rebound damping adjustments are as simple as turning a thumb knob. Spring preload requires using the furnished wrench but is fast and easy. Rear wheel travel is 11.4 in. Fork travel is 11.8 inches and highly tuna-
ble also. Damping is adjustable by changing oil weights or decreasing/increasing oil volume. Stiffness is variable by changing fork springs to optional units or fiddling with air pressure. Stanchion tube size measures a beefy 38mm and double pinch bolts are used on both triple trees. Steering quickness is also adjustable on the G. The stanchion tubes are long enough to be adjusted up and down, altering rake for desired performance.
Both DID rims are laced to small hubs with adequately sized spokes. The rear hub is a new unit with the aluminum sprocket placed on the right side to mate with the new countershaft sprocket placement. Keeping with past policy, the rear brake is full-floating, meaning chatter and suspension lock-up is minimal when the brake is used hard in rough downhill situations. The unit is actuated by a steel rod and has a wing nut adjuster so trackside maintenance is easy. The rear brake pedal is steel with a ribbed top and a static height adjuster is standard.
Bits and pieces on the YZ 125 are great. The shift lever is aluminum, the hand levers are dog-legged, the throttle has a mud guard, the front brake cable is nicely routed through two first class cable guides, all control cables are quality items that don’t need immediate replacement. The chain guide is a solid block of plastic, a beefy #520 chain is stock, electrical connections are good rubber covered one way types and attention to sm^ll details is evident everyplace.
All of the plastic parts on the YZ are new for ’80. The fenders are wide and do a
good job of protecting the rider and they’re fairly bullet proof. The side panels are rear-mounted and don’t protrude. The plastic tank holds 1.7 gal. of premix and maintains that YZ identity of the big bikes. It is narrow and mounted low on the bike so it’s easy for the rider to slide forward when needed.
The ’79 YZ125 felt small; not so with the ’80. It’s a full size bike and feels like it. Although the suspension has grown 2 in. at both ends, the seat height has been raised less than 0.75 in. Most of the credit goes to the new frame that allows more suspension, a thick seat and a reasonable seat height.
The 1980 YZG leaves bloody little to complain about. It starts first kick, and has a gear for almost any situation. Shifting through all six gears is smooth and positive. No clunking, clanking or fuss. The G starts in gear when required to do so and the clutch is a one finger gem that doesn’t slip or go away when used hard. Power delivery is smooth and plentiful and the powerband is wide for a 125 moto-
crosser. Starts are first gear affairs with riders that weigh more than 130 lb., second works well for lighter riders. Once off the line, Honda’s newest 125 will stay with it in the drag to the first turn but, the YZ quickly leaves the Honda behind as soon as rough ground is encountered. The YZ has suspension as competitive as its engine. The G will swallow the deepest whoops in a straight line yet behaves well on the smooth sections. The light weight makes throwing the bike into corners easy and it never tries to tell the rider how to ride or what style to use. It is responsive to the lightest input but not to the point of being touchy. Brakes stop the YZ quickly and positively. The YZ125G is an extremely narrow machine. The rider can crawl all over the bike without hitting his knees on anything. Even the pipe is out of the way.
We couldn’t find anything on the YZ that needed changing to be race ready. Even the Bridgestone tires (M21 front and M20 rear), work great. They grip well on hard and soft terrain and last a long time.
Our pro rider raced the bike several timesr and didn’t break anything, not even a spoke. The spokes did require constant tightening though. They loosen noticeably every moto. Once the suspension is dialed for the rider, the bike almost becomes an extension of that rider. He can choose any
YAMAHA
YZ125G
$1329
line through a corner-high or low-it doesn't matter to the bike. Square turns are executed as easily as bermed ones. When using the berm, the YZ stays ex actly where the rider wants it, it doesn't wander or climb over the edge, nor try to cut low. It is completely neutral in any cor ner. Any riding style fits the G, even styles developed on other makes of bikes. The rider doesn't have to develop any special style or adapt to machine quirks. Longevity has been a problem on some of our past 125 motocrossers. Our test 1979 YZ125F was very short lived. The rings were worn out before we completed two days of testing. Our G was just the opposite; after three days of testing and five pro motocross races, it was still going strong. Problems during the test and race period amounted to one thrown chain (we soon learned to keep the chain fairly tight), and a continual loosening of the spokes. Otherwise, we had no problems and no complaints. And the bike proved competi tive in the pro class in completely stock condition. What more could one ask?
