1981 Yamaha G1 Mods

[jimdurt]

I believe I need a clutch. May search around for a used comet. Any particular model I need?

[chompy]

Originally Posted by jimdurt

I disagree completely with Chompy. This engine is based on snowmobile technology. It has alot of potential. Just need to give it time and LOTS of trials.

Chompy - What is the difference in "port timing" you speak of? Why will it not produce power?

I will try and dig up some information on the Blaster port timing and maybe get some comparison data to see what is different. Anyone measure the cylinder head bolt spacing between the two?

Port timing is where the transfer holes are in the cylinder walls. While the bottom on the engine is based on a snowmobile engine the top end is not. I have the original snowmobile cylinder and I can tell you that it is totally different. Intake from the carb is much lower on the original and the exhaust is much higher and wider. The transfer ports are wider and slightly taller. The top end of a G1 was built for use as a golf cart. Since 2 cycle engines don't have valves to regulate intake and exhaust they rely on port timing and exhaust back pressure to control fuel inflow and out flow. The term "tuned exhaust" was coined because the exhaust pipe was built to the specs of the engine exhaust port timing for backpressure to keep fresh exhaust from exiting the engine at a certain rpm. On you golf cart your going to find that a longer head pipe produces more power at low rpm and a shorter head pipe will produed more power at higher rpms. Either way they will not give you the power of the original snowmobile design with the stock G1 cylinder.

[sho305]

Originally Posted by chompy

...I have the original snowmobile cylinder .....

And?

It seems easiest to just convert to a Bravo engine if you want a lot of power. The old sled engine may be hard to come by and the newer ones run much better though at higher rpm for some. Personally I always wanted to try the 300 or 340 twin they sound so cool and likely would make plenty of power for a cart. I have a 440 but no cart yet. The Bravo and Enticer engines are fairly mild far as 2 strokes, however one should still expect more noise and clutch for more rpm and more smoke/etc. More or less why they don't put 2 strokes in carts for a long time now. Plus you have to fit the huge pipe in there. A good pipe at rpm it works at, will actually pull fuel/air out the exhaust and then ram it back in just before the exhaust closes. That is how it supercharges the engine. The port timing is critical for this to work. That is why say a motocross bike or sled can make far more HP than a 2 stroke outboard that does not have pipes. Of course it limits usable rpm to that band it works at. Just the same a newer 700cc twin in a sled is making around 120 or more HP these days, stock, and very reliably. My friend has a 900cc Cat all stock is 160HP I think, its a rocket, will idle nice and drive around the yard at 10mph or bust 100mph on a lake like nothing. Piles of cash but take a look at what can be done http://www.psipowerinc.com/34692.htm

On the other hand there is nothing wrong with playing with the G1 engine, just realize what you have and if you want more than it can provide...you will have to use something else. There is also a place that ports G1 cylinders, I forget the name but someone knows.

[JcXtreme72]

Did you ever get any more progress out of your project?