1981 Yamaha G1 Mods

[jimdurt]

Ok so I have installed a Yamaha Blaster pipe and muffler on my cart. Dont have any results as to the effects yet. I will have the cart back together this evening. I also have a Blaster carb and reed cage.

Just a note to everyone, the Blaster reed cage is identical to the G1s. The only difference I see is that the Blaster have composite reeds versus the G1s stainless steel. No difference in size on either. The carburetor however is different. The Blaster carb is Much bigger. Don't know how this will effect the cart but I will keep you updated.

Anyone care to share their experience with larger carbs on small 2 strokes?

[jimdurt]

Ok I got her back up and running. Seems to be lugging REAL bad now. Like it is not getting enough fuel. Think I may need to play with the jets.

Also I have the stock carb on it still. Anybody using hotter plug on their G1. Mine seems to be awfully cold. No white ash or brown. Just dark black. May try a hotter plug.

I dont believe I am running rich, cause when I peg the throttle it wants to go but needs more fuel.

Any suggestions?

[tikicart]

With the blaster pipe to need to lighten the weight or get a stronger spring in your primary clutch in order to "get on the pipe". The had better luck with the Banshee pipe than the blaster Blaster pipe but this may have been the primary clutching. I am running around 125 grams of weight with the orange spring in my Comet clutch. I don't know how this would correlate to an OEM clutch, but either way you will need less weight in the primary to get your RPM's up.

[jimdurt]

Maybe a stiffer spring would also help out. I may try to lighten the weights some, but will first try a spacer on the spring to stiffen it up a bit. Still waiting for my carb kit so I can put my Blaster carb and "Boost Bottle" on it.

The cart should have the same or more power as a Blaster do to the size of the engine. Just need to get the carb and exhaust dialed in. If it tunes good without a belt on it, then I will worry about changing the clutch around.

Thanks

TikiCart - Hey will your cart spin the tires? Is your rear end locked? Im not looking at high top end, just alot of low end torque to spin the tires and cut donuts. With the stock pipe and carb I could spin pretty good on grass but only when cutting donuts.

[chompy]

You may be in a little disappointed in your quest for more power. The port timing of a G1 cylinder is not set up for the kind of power that you are looking for. Usually two stroke mufflers are built to match the port timing of the cylinder and the specific use of the vehicle. You may need to get some porting work done to get close to what you want. Not saying that you won't get some results but it may not be what you are looking for.

[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?

[sho305]

Mostly the height of the exhaust port determines what rpm it will have power. Closer to the head the port is the higher rpm it will make power at. Size and the other ports change things too but the exhaust is the most important. I did raise my G1 about 1mm, but still had the stock exhaust. It helped it rev out a little more for more top speed. The piston/port opening event at X crankshaft degrees is the same as a camshaft opening a valve in a 4 stroke.

There is a reason sleds are clutched to take off at 3K rpm or whatever, because with a pipe and porting to run 7K on top they make no power under 3K. IIRC the G1 was originally derived from a snowmobile the GP series from the early 70s possibly. They did have a 400cc then but not sure its the same or not. On the other hand they did not port sleds that radically back in the 60s and early 70s, a daily sled could not work well that way until later.

Another hotrod thing to do with old yamahas was to cut the top of the cylinder down and add gaskets to the base if needed; that raised all the ports. If you added less to the base it raised compression long as you still have piston clearance.

You could also experiment with making the header of the pipe longer, that will lower the rpm it works at. If you made it shorter when you mounted it, that is not good, many people don't realize the chambered pipe is based on the speed of sound. It will reflect the pulse back into the cylinder at the timing of the sound speed the length of the pipe and back. There is more to it of course, but loosely that is how it works.

Also adding a larger carb will do the same thing, it will have more top end but bog on the bottom. Be very careful about jetting with a 2 stroke and a pipe. A little too lean and you will be putting another piston in it, but that is where it will run the fastest. Its not such a problem with slower motors but when you start making good power it is.

[jimdurt]

Well I have been through 2 different piston kits on my G1 and the compression has never been higher than 90#. First piston had too much ring gap. I used my old rings in the new cylinder after careful filing of the ends to meet specifications and still no improvement. I am in the process now of removing the head gasket and lapping the head to the cylinder with grinding compound. I will then use Form-A-Gasket #3 (Aircraft Grade) sealant in place of the gasket. This should increase my compression.

So in terms of the carburetor, do you think the stock carb is better than the blaster carb?

Also what is the size of the stock G1 carb?

Blasters are 28mm, right?

[sho305]

I don't recall the stock carb size. Who was the guy with the yellow G1 he put the jeep front end on? He put a larger carb told all about it, will have to search back a while to find it. Thenewguy might know who that was. There are some good G1 threads on here some on BU as well but they are hard to dig up.

[tikicart]

To answer your question, no it will not spin the tires, but I am running 22" tires also and I have no grass to play in. I will probably lock the rear end this winter since the cart can't be down, its used as main transportation to the lake in the summer. I have plenty of low end torque can pull 3 adults up hills at around 14 MPH. I have the clutches dialed in to have some "slip" at take off, the RPM's just spin up and the cart goes faster and faster, until I run out of driveway.