So, this is the 250 I mentioned in another thread with the bad engine, it has a terrible top end tap/knock which I suspect is little end and piston/rings.
Since owning it I’ve not used it because of the issue but it’s never idled as it should. Before I even attempted to fiddle around I ordered a carb rebuild kit to which I have now fitted.
All the jets were the same as the old ones I removed and I replaced every seal as expected, but still it won’t run properly.
If I fore it up from cold the idle is to low and I have to apply very slight throttle to keep it running, when it’s warmed up and you ride around for five minutes the idle sits high (at a guess around 2000rpm) and shows no signs of dropping even if I give it a rev.
Now my first thought was that the carb must be sucking air from somewhere, so I sealed every possible point that it could suck air from but it made no difference.
I’ve tinkered with the carb endless amounts of times and even stripped, cleaned and rebuilt again but to no avail.
All I can think is that the carb is worn out or has a hairline crack that opens up when it gets warm.

Any ideas?