Hi Nige

I see you have a nice setup with your engine.

ALso, if everything is set properly you shouldn't have problems with your engine, so I think as people has said, there should be a problem regarding air leaks in the carb or backplate, you should look for them. Also, if your engine is set for high nitro (lower compression= more head shims) you shouldn't have any problems running on low nitro, despite a little less power. THe inverse I think will give you some problems but I think the engine will run anyway.

Tighten head bolts and so, and also try lower nitro fuel, using straight castor/methanol fuel as said before is a good starting point. Your problem must be a minor one, not a problem that makes the engine deserve a bad reputation.....do a search in your engine and let us know.

Jorge