G1 engine build project

[MXTex]

I continue to gather information. Yamaha part # 3TT-13621-00-00 is for the gasket that fits between the reed valve assembly and cylinder of the G1. A cross reference of this part number shows that it is used on quite a few Yamaha motors including a 1983 YZ80. What this means is that the carb joint and carb from a 1983 YZ80 will bolt right onto this G1 motor. Stock G1 carb is 16mm. YZ80 carb is 28mm. Not sure the carb joint will hold the carb at the right angle though.

[1989Marathon]

Here's the video.
What rpms are you looking to turn?

http://www.youtube.com/watch?feature...&v=QNFBJDzMfUY

[MXTex]

That's impressive Marathon. I really don't have a target rpm range. Just want it to scream....lol. Yet still have reasonable bottom end. This cart is purely a pit vehicle at the races. There will be no golf course duty. For these reasons, I don't want to go nuts on carb size. On my sons KTM 200 dirt bikes, we ran 39mm carbs. So I know 200cc can support a lot of carb. But those bikes were high rpm screamers all the time. For this thing, I think a YZ80 carb at 28mm might be just what the doctor ordered. A substantial increase over stock but not overkill by any means. I just need to figure out the carb joint.

[1989Marathon]

I made my own carb joint. If you look in the video, it's just a 1/2" aluminum plate with a Mikuni rubber carb flange mounted to it. The plate has a center hole to match the size of the carb flange, and 4 holes for mounting.

[MXTex]

Well, my engine project went dormant for a while. But I'm getting going again. Included herein are pictures of the cylinder porting and case matching. Comments welcomed.

[ekaybe]

Can't wait to see you making progress on this build again!

[TheGDFP]

4 month bump :)

Did you get any port measurements before and after porting?

[85.G3]

Originally Posted by sho305

I never found a good answer on that (and not having google time right now), though I doubt its on a golf cart engine because it makes more power. The banshee had a boost bottle, I was under the impression it was for low rpm or idle quality or something like that. Personally I would be reserved to change anything unless I had good info, the G1 is very proven. I was riding them around when I was a kid and they were brand new, and I'm not a kid anymore, and they are still riding around lol. Oh wait, I was maybe jumping them at times...

The link below is a good explanation on boost bottles. We had them on the older Yamaha MX bikes but as I recall they went away about a year or two after they came out. I think the variable exhaust valves eliminated the need. I don't recall anyone but Yamaha having them

http://www.2-stroke-porting.com/Boost_Bottle.html

[copperhead1971]

Originally Posted by MXTex

That's impressive Marathon. I really don't have a target rpm range. Just want it to scream....lol.

great work... but if you want to scream, just wait till your all done ,sit down on you new ride and open all the bills to make this speed demon,that should make you scream