just bought for my son ...runs sweet on stand ..when rev it up to 5000 it starts to vary ..between 5000 and 7000 cleaned plug.nd card ...bike has also started to backfire ..when running on flat road seems to be choking ..struggles to get over 7000 rpm ..engine seems to die ..any help would be great thanks

daniel jones, October 2009

john
have stripped carb and cleaned have cleaned filter on fuel tap new plug runs sweet on stand ..took it for a run ..when slowing down ..starts to choke its self again ..no back fire ..but if you shut throttle and slowly open again ...engine picks up ...could it be variator balls worn do you know how many turns the mixture screw should be out

dave...daniels dad, October 2009

OK check over the filter in the fuel tap (vacuum operated on these maybe)? Is the air filter clean? Sometimes bikes like these suffer if they are fitted with after market 'sporty' accessories! You did mention a backfire...worth a new plug. The bike will be fine on the stand as there's no engine load....it will only show its problems when its trying to get more fuel, I think.

John, October 2009

john not kicking back through carb..runs sweet on stand and tick over is sound ..but when riding dies on me ..if you close and re-open throttle it picks back up ..seems to be choking ..cannot find any blockages

dave, October 2009

If the bike is kicking back through the carburettor, this indicates a weak mixture due to a small blockage. I'd also put a new plug in too.

John, October 2009