So. Here's what I did today.
First I decided let me take the panels off. I want to see what it looks like naked and see how easy it is to get to everything.
Looks rough. Lots of rusty bolts and what not, this thing has some miles on it for sure. So I was like ok I'm going to do the BBK. But wait, screw it.
I removed the whole thing.
Then I removed the wheel and threw it on my patio table. I was hoping all day it wouldn't rain and it didn't. Just a lot of wind and clouds. I decided to give it a cleaning too while I had it out. Well, somewhat of a cleaning. It's still filthy, but it's MUCH better than it was.
So let's take this thing apart and see how bad the inside is.
Huh. The head was still in good shape, no buildup. Hmmm. Let's see the guts. Head gasket looked good too.
The inside of the cylinder was actually damn good, almost no carbon buildup? I started to get scared that this was already a BBK on it...
Clean on the other end too.
Don't worry. I put the two heads and pistons side by side, yep it was a 49cc. Whew!
So off it comes.
The piston itself was actually damn clean too, very little carbon on it and no burns or anything. Either this top end was new(ish) or this thing was very well taken care of. Or it just had very little mileage on it and the ODO was replaced. I think the ODO was because I saw some wire tags with markings on them like someone replaced it. So maybe this thing doesn't have close to 5k on it.
I inspected the crank and rod, virtually no play in it whatsoever.
So with my trusty Rigid Multi Tool and some scotch bright pads, I cleaned off the gasket (with a razor first) and decided to give the surface a good smooth finish.
I figured while I was at it, I'd do the intake too.
Uh oh. Looks like the new head won't fit because of the oil pump. Good thing I ordered a flywheel remover! Off the oil pump comes.
And here we go. I added some MOTOSEAL to the bottom of the base gasket, plus I wanted to check my port clearance. From what I can see, I can probably use a spacer on the head to bring everything up a bit. But I'm not messing with that just yet. I didn't go overboard on the seal so I can take it back apart if need be.
Now to prep the head. A little copper spray. Or a lot really.
Viola.
Finally. She has a 72cc head.
Some things I didn't mention. I used Loctite on the cylinder head studs on the case side and on the nuts too. I torqued them as
90GTVert said, 13ftlbs, then 14, then 15. Tomorrow I'll retorque it along with the exhaust. I was thankful it went together so smoothly honestly. The circlips weren't that big of a pain, the wrist pin and wrist pin bearings fit perfectly and the exhaust even sits a little better with this head I think. I'll take more pics tomorrow to show how the exhaust is mounted now. Still not using the supplied bracket though, but it's damn secure. I even used a tip from
2TDave and used an old roller weight as an additional spacer.
I took it for a run. Goosed it here and there while running 1/4-3/4 throttle mostly. Once I figured out to remove the "pod" from the air intake, it stayed running. It stalled once I got on it but after that it seemed fine.
I think the #90 jet is a little rich for it though? I don't know. It seems like it has that waaahhh at the top end and my top speed is hell. But I know I've got some CVT tuning to do now. It takes off nicely, but I noticed that the RPM are way off now. When I take off, it climbs up there better than before but then suddenly it flies right to 9k RPM (HOLY SHIT 9K!??!?) but then drops down to around 7,200 and wont' go above that. I think I still have 5.5g weights (5&6g staggered) in it. I have the Dr. Pulley sliders that I got from
2TDave I'll use, they are 6,7,8g. I'm hoping that's why it won't stay at the 9k or go above where it is now. Plus I know the air/fuel situation needs tuning too. It responds great with the fiberglass reeds and all, it just needs top end tuning now.
One thing I've learned is I'm definitely pulling the motor from the 4t when I do the BBK on it. That thing has WAY less room to work with than this thing did. But I'm glad I finally did it. Now I see there's a few things I need to order, like a shroud. This one is barely holding on and vibrates like crazy. actually, the whole bike vibrates like crazy now.
I just opened a can of worms it feels like lol.
