Upgrade to enjoy this feature!
Vital MX fantasy is free to play, but Premium users receive great benefits. Premium benefits include:
- View and download rider stats
- Pick trends
- Create a private league
- And more!
Only $10 for all 2026 SX, MX, and SMX series.
The Shop
Free shipping: VITALMX
Luxon 4-Post Bar Mounts
$189.95 - $239.95
DeCal Works Huge Plastic Inventory of UFO and Polisport kits.
My first bike in 1973 was a GTI 80 Yamaha. I raced my GT 80 3 races in 74 then parents bought me YZ80A 1974(Grey Red strip Tank). Just a few months later, the YZ80B 1975 (yellow Blk tank) was being sold. It had so much more power than the YZ80A.
Since the YZ80 was introduced in 74, they all had 5 speed trans., and the motor was completely differnt from the GT80s and GTI80s. My last YZ was a 1977 YZ80D.
I don't know what yr they went to a 6spd tranny.
My 75 YZ80B, mid season, I did get that Turtle Suspension lay down kit for my bike, and purchased Boge shocks like Myerscough's bike. He has some trick springs on his shocks. The Turtle Kit was basically just a piece of metal that had to be welded to the subframe for the top shock mount to lay down. It was very cool!
I wish I had the front forks Myerscough had to compliment the rear suspension.
In '76 the YZ80 stock bore was 49.00mm, making it 79cc. The first two tears of YZ80 production, the motor was based on the 72cc design. The cases may have been different than the GT's, but bore and stroke were GT based.
Basically,the 74 and 75 YZ80 engines were hopped up GT80's from the factory.
I don't profess to know everything and I enjoy feeding off or on intelligent people and their experiences and wisdom. "In order to be a Great Leader, you have to be a Great Follower!"
For me, you see what you get, I don't pretend to be something I am not. My talk is straight, period.
Bore, Stroke, 72mm, etc..., we can go on all day about the mechanics of the bikes, but Please don't call the GT80s and YZ80s in the same league.
I don't know where you are getting your info from, but 74 and 75 yz80s engines were not hopped up GT80s from ANY FACTORY!
They didn't just slap on different cases on a GT motor either.
So Basically?!, PLEASE just stick to the facts.
Remember, I owned 74, 75, 77 YZ80s,(my parents and I couldn't afford a new bike in 1976) and I just raced a short season of a few races in 76.
Matter of fact; my younger brother had a TY80 also.
Now yes, the GT80 and TY80 shared the same motors, though different internals and gearing(obviously) suited to the style of bike and type of riding.
The 1973GT80 was a great first bike(mine was 73GTI80).
The1974 YZ80A was so much better, handling and much faster, but still pretty slow compared to a stock XR75 which was so much faster.
The1975 YZ80B was so much faster than the YZ80A.
The 1977 YZ80D yet still better bike. I still liked my 75 YZ80B the best out of all of them.
Midway through the 1975 Mx season (District 14) my YZ was completely stock, for my birthday(July), my brothers and parents purchased the Yamaha GYT kit that came with a Skyway Silencer on the expansion chamber. It was the best sounding bike period(not the loudest). The bike was rev-er, all the power was at or near redline. Clutches didn't like it. At the same time, they purchased (brother Todd) skunk lay down kit and Boge shocks. Todd took my bike to Staten's to weld up. I do remember the first time firing it up! Wow! A 12 yr old kid, it was pure Bliss!
I couldn't have had a better life back then, and didn't take it for granted. I worked on my bikes, with the help of my brother. I could change pistons and rings and most basic mechanicals except for splitting cases since my first bike at 10 yrs old.
I like this site and welcome great stories and information which I enjoy reading and learning, though I don't like words and mis info that is a waste of my(our) time. This why I don't hang around liars, cheaters, and people that steal.
Before you go calling someone a thief, liar,and cheat, you should know WTF you are talking about. You still act like you are 12 years old.
If you have owned and worked on that many YZ80's from 74 to 77, and you can not tell the difference between a 47mm piston and a 49mm piston, your bikes were probably slower than your current train of thought.
The FACT remains ,the first two years of YZ80 prouduction were 72CC ,GT80 based dimensions.
Now go play in traffic.
PRS395- a stock XR75 was faster than the YZ80? Wow, I would never have expected that.
Tripled the horsepower, and revved it's ring off. About 13,000 rpm if I remember right. Good way to teach a 10 year old how to ride. 125's in comparion were torquey.
I want to correct myself, and do not want to label you a lie, cheat, stealer, since, you took my blanket statement personal. I don't know you. I will start over.
What you said before, "Design" to now, "Dimensions", which has been my point from the beginning.
I also forgot left side outside case looks almost the same if not same for yz / gt. So I get what you are saying just by looking at L H Side. We did shave cases to expose the countershaft sproket on my bikes.
I will take your expertise on what size the bore and ccs
What ever the specs; The yellow tank YZ80B (first yellow tank yz80, 1975)
was waaay faster than the Grey Tank YZ80A, weather they both were 72mm or not. Much of the HP gains were visable to the eye when comparing the
A and B.
Matt;
I raced this kid(he wanted to see what my bike would do, and so did my friends) on a dirt road, I being scared that the cops might catch us riding on a public road. On my stock(only having the bike a couple weeks (grey tank)1974 yz80a, this kid walked all over my bike, in the middle, especially top end.
DropBear I would almost give an eye to have a Nogouchi kit yz80 back then and now.
Pit Row
It was just a lot easier to make the 2 strokes faster. Just a pod filter and a pipe and the YZ80 was away.
Of course the YZ80B blew them all away. The following year. The gates were 95% Yamaha that year.
While Yamaha may have developed a new chassis,suspension, bodywork for the first two years of YZ80 production, the fact remains that the engines were based on the 72cc design of the GT80.
I am sure there are some slight porting differences between the GT and YZ ,along with a slightly larger carburetor and different pipe design for the 74-75 YZ80.
Yamaha's first ever YZ dirt bike's engine was based off a DT-1 enduro. The first two years
of Yamaha's YZ80 were based on the GT80 engine design / dimensions. That's the way it was. Not saying they were not faster than the GT80. They were not even full on 80's for the first two years.
Very good memories!
Measure any standard Yamaha,Wiseco or any other piston for the 75, and it will be 47mm. The 76 will be 49mm.
There is a reason why all piston manufacturers show the 74-75 YZ80, the GT80, and the TY 80 using the same piston.
The 76-80 model YZ80 uses a different piston, because it is for the 49mm bore.
47mm bore x 42mm stroke will put you just under 73cc. This is what a true 75 YZ80 measures out at on standard bore.
If your bike has a 598 code cylinder on it, it will be 79cc, as that is a 76 C model cylinder.
Checks out . Montesa Cappra 75cc winner of euro 75cc champs
Post a reply to: Who rode this mini and....