Hi again people! I've just started the bike for the first this summer :-)

I had to clean the spark plug connections but other than that it started/runs pretty well, but only with the choke open! As soon as I close the choke I can hear the engine start to struggle, and then die pretty quickly. The revs do not pick up when I turn the choke off, even momentarily.

I've read on here that I may need to clean the carb or that maybe some of the rubber boots on the carb may need replacing? Is this right?!

It's a Yamaha DT125 R, around 1990. The only other thing that may make a difference is that the power valve is not operating. The bike has been stripped of batterie etc hence no power valve. It has been fixed open about half way but this was the case well before the choke problem/cut out started.

Any help for this silly amateur would be much obliged :-)

almost definitely a blocked pilot jet, especially as it has been standing. The fuel in the bowl evaporates over time and forms a jelly like substance in the bore of the pilot jet.

The way to prevent it happening when the bike is laid up is to open the fuel cock every month or so to top up the bowl....for future referance

This...assuming it was warm enough to knock off the choke in the first instance

Cool thanks mate :-) Any advise on cleaning/unblocking pilot jet? Much appreciated

take it out, use a magnifying glass to verify it's blocked. clear it with a soft bristle pulled fron a nail brush or the like and blast some aerosol carb cleaner through it and the place from whence it came