I have a strange issue with my S50 that I need some advice on. Every now and again during a WOT run, the engine will suddenly start to bog down and blow lots of smoke out the exhaust as if it is running overly rich. Backing off the throttle and gunning it again clears it out and its off. I can run it around for 10-15 minutes before it happens and it might not happen again until the fuel runs out. All other times it runs perfectly, accelerates cleanly all the way to the top of the rpm range, pops wheelies on demand, idles cleanly for as long as you leave it sat there. It doesnt seem to be causing any problems its just really strange as to whats causing it. I did have a problem earlier in the year where the mid-range needle had undone itself but this has been sorted and doesnt seem to be causing any running issues. Here is what I have tried so far Stripped cleaned and sealed engine - no change Changed fuel (same % and brand just different batch) - no change Changed plug (OS8) - no change Checked fuel and pressure lines for leaks - no change Replaced o-ring on HSN needle - no change As you can see it is a bit of a mystery. If anyone has any ideas I would be happy to hear them. Mike