I know this was a daft thing to do but started up my van a couple of weeks ago, having being sat for 2 or 3 years, without flushing out the tank. Started and ran fine but tried again back today and it won't start. I guess I've pulled some muck through from tank but where should I start looking? Have fuel at the carb and will almost fire but not quite. Tried redex through air inlet but no joy. Any suggestions? Thanks