Okay I get what you mean by burning out the exhaust now, I really don't think that would be an issue on this bike, with such low mileage.

I just tried it out with the spark plug gap .020, and it actually made it worse. Now it starts cutting out in 5th gear at around 5200 RPM. So I switched it over to the other plug that has gap around .024, and it started cutting out at 5,500 RPM again, only in 5th gear.

I'll check the coil values, and take the side cover off and see if I can check the points gap with a feeler gauge.

My personal feelings are: ____________.

If you do not run RACING FUEL 106 - 110 Octane it probably will not do what you want or expect?
Be aware you’re probably going to hear some very loud banging and crackling before you complete this..

a

I pulled the coil and checked the primary and secondary ohm values, and they were within spec.

Using a feeler gauge it seemed like the point gap was around .015. I tried using some fine sandpaper on the points, then decided to pull the flywheel and stator and remove the points to clean them.

They actually were pretty well pitted and corroded, and I've got them polished down to a mirror finish now. Also, the wire connected to the points was only hand tight. So between the pitted points, and the loose wire, that could have contributed. We'll see...

EDIT: Well drat, it didn't help. Beginning to think it's a fuel starvation thing. It almost seems like it's starting to run out of gas, and backs down to an RPM that whatever supply it's getting can maintain. Maybe it is that petcock, the interior tubes are a lot smaller than the original one as well.

If your latest changes to the ignition don't help, I would try to go one size richer on the main jet.

You don't say if there is any stuttering or sputtering at 5500, or if it still runs smoothly.

Yes, it is stuttering and sputtering at 5500 RPM only in 5th gear. In 1st through 4th I can go up to 6500 RPM plus and it runs fine. But once I'm in fifth gear, as soon as it starts approaching 5500, it starts sputtering and won't go above 5500. I've forgotten everything I knew about carburetors, so I've been reading up on it and you might be right, I may need a larger main jet, because that controls wide open throttle.

Try a test run without the in line fuel filter.

Don't forget that very important little Oring No7

O-RING
93210-04230-00
www.partzilla.com/product/yamaha/93210-0...ca5568ea37580c239f35
www.partzilla.com/catalog/yamaha/motorcy...1971/ct1c/carburetor

I took a test ride without the filter, and it was the same.

Is O-ring number 7 at the very bottom in the recess in the carburetor bowl?

If so, is there a hardware store equivalent to it, or does it have to be ordered through Partzilla? Every time I order a tiny part from Partzilla, it cost $1 for the part and like $15 for shipping.

I took the carburetor apart and looked at it closely again, and if that's the O-ring you're talking about, it is not in good shape.

I also found a little bit of gunk in the main jet. By the way the jet is a 150. I cleaned it up the best I could and put the carb back on, but it's too windy to go riding again today. Almost blew off last time I rode!

At least I'm learning a lot about how to take this bike apart and put it back together LOL!

I am glad I got the points cleaned up though. Also put a tiny bit of 30w oil on the felt, it was pretty much dry.

Yep be careful out there. No7 sits on a screw in thingy straight up the middle into the needle jet. It retains the needle jet & i guess you've not had that out. They get crudded up around the outside. I just screw a 5mm screw in a turn or two as thread will be a bit different then tap the needle jet out the top. & it has a guiding pin to locate it at the bottom so it points the right way. Anyway--Oring fits on the screw in thingy & seals into the bowl. If yours is still ok you'll feel tension when sliding the bowl on. If no tension then it's toast, replace it. I don't know if i'm on the right track but 'is' an important item regardless.

this is the part number but don't know the freight cost which usually scuppers the deal, or does where i am, half a world away.

www.boats.net/product/yamaha/93210-04230-00