Ok Boffins Im stuck, bike lost power, I know it shouldn't have a lot but it has EVEN less now. Starts ok idle is ok but when I ride its lame, its lifeless and no its not a LIFAN its an original Yamaha. I cleaned the carb AFTER getting a mate to help loosen screws but even thats not helped - it was ok then but now its intermittent sometimes its 75% ok other times 50% rarely 100%. Cant imagine what else it could be? Spark is ok, the air intake is as close as it can be (never a great fit anyway) so is it just another carb clean and hope what ever is in there I eventually remove?? Could the mixture be out?

hi hav u checked the electrics? just make sure ur battery terminals are clean and that the connections are on tight.

try the cr7hsa spark plug thats what iv got in mine and it helps .......a little lol

(think the original is cr6hsa )

try and get a bigger main jet dont know what size is in urs but mine is 77.5 and iv put an 80 in it and it helped the torque out loads.

also check the conections to the cdi they might of come loose.

hope this helps .

oh hav u also cleaned ur air filter? might of got clogged

Make sure both cylinders are firing, I had (have) an XV250 it ran perfectly for 7 years - used it everyday - about the only problem I ever had sounds almost exactly like yours, it would start, tickover and sounded OK - but was only firing on one cylinder had no power, top speed about 30mph (downhill) - sounds silly I know but the mufflers on the XV250 are linked and its not easy to tell if both cylinders are firing...

I seem to remember it was an HT cable adrift (under the tank)

Geoff

Starts ok idle is ok but when I ride its lame,

What happens if you pull the choke on? is there a sudden improvement?

This will indicate if it's a fuelling issue.