The History of the Yamaha YZ80 from 1974 to 2001.
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History:
The Yamaha YZ80 was a two-stroke motorcross dirtbike produced by Yamaha from
1974 to 2001.
Altough the YZ80 is a good bike for expert mini riders due to an abundance of high
rpm power and good suspension, it has too little low-end and midrange power for
most riders.
The problem is a combination of radical port timing and high gearing.
Like most of the minis, the YZ doesn´t have the quick response to keep up with the
RM´s out of turns.
1993-2001 Yamaha YZ80
Flaws: poor low-end power, non-adjustable forks
Fixes: cylinder and head mods, adjustable base valve
Cylinder mods:
Here is a way to get more midrange power from the YZ80. Turn down the base of the cylinder
.028 inch or 0,7mm and remove the same amount from the squish band of the cylinder head.
This retards the port timing and reduces the port duration, plus increases the compression ratio.
Intake:
Install a set of Boyesen dual-stage reeds for better throttle response.
Expert riders prefer changing to a larger carb (28mm flatslide Keihin) for more overrev.
Gearing:
The stock gearing is too high and should be changed to 12/52, for quicker acceleration.
Gearbox:
Earlier models had problems with the wear on the gear teeth of the second gear.
Yamaha has since improved the gear and pulled all the old parts from stock. If you ever have to
split the cases for engine rebuilding, check the gear teeth for wear. The wear pattern looks like
corrosion. Replace the worn gear and the corresponding gear.
Clutch:
Yamaha recommends switching to stiffer springs. The part No. is: 90501-216A6.
Forks:
The forks can be improved greatly by installing an adjustable base valve kit.
This makes the forks plusher. There are two options for base valves: 1992 YZ125 OEM base valve
or a tuned valve from Pro-Racing or Race Tech.
The stock fork and shock springs are too soft for most riders. The way to check the spring rate is
to set the race sag to 75mm in the rear and check the unladen sag (bike´s own weight without rider).
If the unladen sag is under 10mm, then you need to install a stiffer shock spring.
The front fork sag should be between 20 and 30mm. If the forks sag more than 30mm then you need
to install stiffer fork springs.
1993-2001 YZ100 Conversion:
If you want to convert a YZ80 into a big-wheel 100, it is possible with a combination of aftermarket
engine and OEM parts.
!!!KEEP ON BRAAAAPIN!!!
DirtBikeDudeZ
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