The bike starts up 2nd prod ticks over great, no smoke.I did a top end rebuild so still running in .Changes gear , but will not do more than 35mph  at 4/5000 revs in 5th , ive blipped it up  too 7000 but no diff to top speed ,. i weigh 200ilbs,Any ideas please.
           Regards GB

Not easy to guess at that one. Does it rev & pull hard through the lower gears to 7 grand then fall over in top gear or just flat all the way [thinking restricted exhaust in the built in non removable parts deep in the tail end [spark arrestor part] or that item might be part of the removable end parts but should be obvious with a light in the end looking deep in. All a guess but gotta start somewhere. Could also be points gap closed down to almost invisible which effectively retards the timing & turns horses in donkeys. That's my first guesses.

I don't understand. It does 35 at 4000 or 5000 rpm and 7000 rpm in 5th gear?

Could clutch be slipping?

Speedo is bad and won't read over 35?

Carby little Oring leaking which can richen mixture greatly. Wouldn't rev though if it had a bad leak. [seals main jet into the needle jet].

I weigh about 200. Most 15hp CT1 - **** should pull about 55 mph no problem.

clutch - is there 1/8” free play in the clutch lever?
carburetor - is the jetting standard and are you at 5000 feet elevation?
tires - add two pounds regardless to eliminate that.
gearing - is the gearing standard or modified?

Yes, my AT1-C had a cruising speed of 35 mph. Not flat out, just enough to scoot ….

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I weigh about 185 and my '71 CT-1 will do 65 MPH on the speedo, which I discovered is really around 62, with a GPS app. I went up one tooth on the front sprocket, but I think it might even wind out faster with the stock gear. It's cruises great at 45-50 around town.