Hi Thumpeteers
As you know I have been wittering on about my GN250 and oil for some time now and I promise to stop soon, but I have a theory that I want to check with you clever folks before I just give up and accept the Mighty Midget as it is.
When I had a look at things this weekend gone I was surprised by two things; first how lovely the plug colour and condition is and secondly by how much soot there is on the exhaust valve stems and port. I tightened everything down and after doing that the exhaust now smokes a lot less for a much shorter time than before.
Now at the same time as tightening down the head I also let the oil level drop to nearer minimum than usual and here is where I begin to think differently about the smoking exhaust. The head of the GN250 has a lot of oil in it, the cam for instance runs in an oil filled trough. My friend and I have always doubted the MM's ability to scavenge its oil at a satisfactory rate. When starting the bike it doesn't smoke immediately but takes a good minute or so to start smoking then clears and then runs clean until parking up again when the cycle is repeated.
Given the state of the plug and the exhaust ports is it possible that with a higher oil level there is oil running down the exhaust valve stems when parked which is then burning off when the exhaust gases heat it up and the engine itself isn't 'burning' any oil? Maybe when the oil level is slightly lower there isn't as much surplus oil in the head for it to drip down the stems.
What do you think oh clever ones? I have always believed the rattle and smoking are design issues given the reports from other GN owners about exactly the same things, maybe this is one of those issues?
I feel much better now towards the MM as the plug shows a healthy engine and it runs beautifully, if a little noisily at tickover. I would only consider swapping it if I could stretch to an XT500 or similar as it is such a lovely little thumper to ride as long as one respects its limits.
Answers on an unsigned cheque made out to CMC Motorcycles please.
Spartacian the slightly less baffled. (hopefully)
