Hey, there’s just not enough information on the Yamaha Chappy out there on the web. I just obtained one after looking for nearly four years. I will update my progress with it as well as provide information that I discover along the way. I’d like to find a service manual for this bike but no luck so far.
Stock main jet. The stock main jet on this 1976 LB80 was 65. Turns out that Yamaha varied the main jet size depending upon the year and model. I found other 1976 LB80’s that took a 90 stock main jet. I have no idea why there was such a disparity in jet size. Perhaps I’ll find out later.
This Chappy also came with the stock exhaust but the MLM pipe is currently installed. As you can see, it also sports the MLM front rack. Too bad MLM doesn’t make a rear rack to match. I’ve got a few things to patch up yet. I checked the main jet size because the previous owner told me that he did not up-jet after putting on the MLM exhaust. I think he only rode it around the block once with the new pipe. Turns out that somebody in the past had drilled out the main jet to a 75. The spark plug also looked like the bike had been running rich. I should be good with that jet. I’ll put a temperature gauge on it just to be sure.
The tail light wouldn’t light up when you turned the key. A new fuse was in order. Both brake switches need to be changed and I need a new fuel cap. I’ll add further updates as I go.
3/2/19 update – I switched out the right control lever and now I have a brake light when I pull the front brake lever. I have a suspicion the “75” main jet is too rich and received a 65 and 70 main jet. I’ll try them later. I took the Chappy out for a ride today and after warming it up well, I hit 44 mph. It might have hit 45 with a little more highway or roadway.
Unlike the Yamaha qt50 and mj50, the Chappy (at least the lb80) has a dipstick to check the transmission oil. Max air pressure for the tires is 36 psi and, although it rode a slight bit rougher, I think going from 15 psi to 36 psi in the tires helped my top end.
One problem you will find on these two speed automatic bikes is that the shift to 2nd gear kills the rpms. So if you are trying to get your pipe to hit, that really works against you. You can try to delay the shift to 2nd gear by shortening the clutch spring. My first line of attack will be to try a smaller main jet. If you are running too rich, the pipe won’t hit. I feel like this engine should be able to handle low to mid 50s easily.
I did find a free Yamaha Chappy Service Manual here. Hopefully that helps some Chappy owners out there.
Also the main jet used on the Chappy is the Mikuni 127-14143 jet. The Mikuni m10/14 jet is the same jet and slightly easier to locate on ebay and jetsrus.com.
The is my first experience with a noped that has such wide tires – 4″, I believe. When you go to turn, it kind of fights you unless you lean into the turn. It seems like leaning is more effective than steering or maybe a combination of the two is the way to go.