Yes mine struggles to get easily over 60 as well although it starts easily runs well enough and ticks over regularly but the doubt about its overall performance remains.
I've always changed the oil every 1000 miles with good quality motor bike oil.
I wonder if a compression test would help?
I seem to remember contemporary road tests indicated when these bikes were new the would do 90 mph. Mine's never been able to get anywhere near that speed, even on the clock.

Hi Ian, yes the engine that was in Kevin’s bike was very similar to how you describe yours. It didn’t want to be revved above 6000 rpm, even tho the red line is at 9500 rpm. 6000rpm in 5th is approximately 60mph.
With the freshly rebuilt engine in, I’ve only ridden it with approximately half throttle and that is taking it to 6000rpm. So I’m guessing that once I can rev it higher it’ll most likely zip up to around the 80 mph mark. Plenty enough for what I want it for nowadays.
The original engine always started & never faltered when out riding it, and I covered a few hundred miles on it but could just tell the original engine was tired.
Oh and I changed the rear shock that Kevin had on to hagons, absolutely transformed the whole feel of the bike
Cheers , Michael

Hmmmm....
I know from past experience that even a top end rebuild can be pretty expensive but I'm sure you must be right about the difference in performance between an old and newly rebuilt engine (if done correctly).

Well I know from owning my first RS back in 1981 which I bought new, that regular oil changes are the key to preserving the RS engine. Because it’s a mesh filter which cannot be accessed easily, they tend to be left un maintained. So if the oil isn’t changed regularly then I’m sure I don’t to tell you of the obvious consequences. So that’s why I used to drop the oil at a maximum of every 1000 miles. I ended up putting a ridiculous amount of miles on that bike, as it was only form of transport back then. I then sold it to big bro in 1986 after running it for 5 years to buy my first xbr. He then ran it for 2 or 3 yrs as a work/ commuter bike.
Ultimately my point being, if it’s not changed regularly then the engine will wear out and start to become “under powered” due to wear. I enjoyed riding the bike I bought off Kevin so much I decided I’d get the other engine rebuilt, properly.
It was far from cheap, however I don’t intend to get rid of the 250 “neo” tracker 🤣 once it’s finished. So went for it, and like I say the difference is amazing 👍
Cheers, Michael

I'd like mine to have a bit more go.

How many miles has yours covered Martin?
The one a bought off Kevin ran as sweet as a nut, but I can’t believe the difference in the feel of the newly rebuilt engine now I’ve popped that into Kevin’s bike. Definitely more pull/torque. I think once I’ve put another couple of hundred miles and swapped the oil, I will start to rev it slightly higher, I’m pretty sure it will be considerably more powerful than the original engine.
I’ll let you know once I get to that point
Cheers, Michael

Hi Martin, yes finally starting to take shape. The body work is pretty much what you see on the photos.  The petrol tank (Kawasaki KH125) and a seat, oh and there will be two S/S rolled mudguards. Colour will most likely be blue, that’s the original colour on the log book, so think I’ll stick with blue, although most likely be a matte finish. Think I’ll also stick with the general theme of the original RS tank, lighter blue with a darker blue stripe down the middle. I’m just in the process of trying to find out the best carb to go with, most likely a Mikuni. Any advice on this would be greatly appreciated.
I’m really hoping to take it down to the oct Stafford show, even if it’s just in its completed but not painted dry build stage. Who knows, if I’m really lucky it may be just finished and painted🤞
Cheers,,, Michael

Oh….. and I found out the other day, apparently the “style” of bike I’m building is known as a Neo tracker.
That’s because it has the dna of a traditional tracker but with modern street bike twist
REALLY 🤣🤣🤣🤣🤣