Brakes, Wheels, and Tanks

The oil tank was half-full when I got the scooter. This was odd, since the license plate had expired in 2000, but I guess two-stroke oil doesn't evaporate very fast. Just your basic cleanup here; I removed the tank, poured out the oil, and scrubbed the tank. There was a lot of white foamy goo in there, which was probably water that had mixed with the oil. I did see that there is a level sensor in the tank. It would be bad if you ran out of two-stroke oil. There is a simple diaphragm-type oil pump on top of the engine. It pumps oil from the tank into the engine. It doesn't appear to mix with the fuel/air charge, so maybe it is a total loss kind of lubrication.

I had read on the internet that Yamaha Riva Razz mufflers are often plugged with carbon, so I pulled off the muffler to check it out. There was nothing loose inside the muffler, and there was no restriction when I blew through it. Somebody had drilled a hole in the bottom, next to the exhaust pipe, probably in an attempt to lower backpressure and increase performance. It probably makes it louder, too. I considered getting out the welder and closing the hole, but I was too lazy. Maybe if it turns out to be really loud.

I took the opportunity to remove the rear wheel while the muffler was off. I had not been able to fit my bike pump or my little 12 volt car compressor on the valve stem. I took the wheel to a gas station and pumped it up there. It is holding pressure so far. The rim looks bad in one spot; rusty and bent. Somebody may have done an amateur job of mounting the tire.

The rear brake shoes are looking pretty low. I would say there is 1/16" or less of lining. I just put the wheel back on and left the shoes alone, but if I'm going to ride this for a sustained time, it will need new shoes soon.

I got the new (used) front brake cable in the mail, so I put it on. It wasn't very difficult; just like working on a big bicycle. The front brake is a drum brake, inside the front hub, and cable actuated. I adjusted the front brake to have very little free play, and the brake seems to work just fine.

I figured it was time to try starting the engine. I put some fresh gas in the tank, and some semi-synthetic two-stroke oil in the oil tank. I hooked up the battery charger, removed the spark plug, and spun the engine for a little while. I had to suck and blow on the vacuum tube of the fuel pump to prime the pump and get fuel flowing. I put in a new spark plug and hit the starter. Nothing. After investigating for a while I determined that the fuel pump was not pumping fuel. The pump worked fine when I sucked/blew on the vacuum line, so that was not the problem. The problem was that the vacuum line from the carburetor was not supplying pulses to run the fuel pump. There's a small chance that I could have screwed up a check valve inside the carburetor when reassembling it, but I don't think that's likely. What I think is a lot more likely is that there is not enough engine compression to run the fuel pump. Which means that the engine does not have enough compression to run, which means that it needs new rings at the very least, and possibly a new piston and cylinder. So the next thing to do is a compression test. I meant to do this when I first got the scooter, but I don't own a compression gauge. So I need to stop by Harbor Freight and pick up my very first compression gauge. Doug's Yamaha Razz web page says that the factory compression spec is standard compression 71 psi, minumum compression 54 psi. That seems pretty low, but the page also says that the compression ratio is 6.3:1, which is in fact low. The air cooled Volkswagon engine I used to compression tests on were around 130 psi, and I would guess they had 9:1 compression. So either the compression will be low, and I'll learn how the SH50 engine comes out and comes apart. Or there was a check valve in the carb where the vacuum line attaches, and I jammed it up while running a thin piece of wire in there to clean it out. Which means I'll be buying a new (used) carb off eBay. Stay tuned.