Seems to suffer more when cold or damp. It starts fine has had a service recently (air filter oil filter fuel filter). It is ok if you can give it a good run on even ground till it warms up but if you take a hill first thing (which wew often do as we live in Devon) it starts slowing down and spews out some black smoke and after about 1 minute of crawling it will pick up and carry on as if there is nothing wrong with it! any suggestions most welcome. Thank you.
Derek