Sounds like more work will be needed, then. If you had a classic engine it would be as easy as making a small adjustment of the mixture screw, but that will be an emissions engine that does not have an accessible adjustment. I suggest the first thing to try is removing the fuel filter altogether: emissions engines tend to operate on the ragged edge of leanness, so even a small restriction on fuel flow might make a difference. Also check whether the level of fuel in the tank makes a difference. If neither of those things helps, and you have checked that the governor linkage to the throttle butterfly is completely smooth and free, it will be necessary to strip and clean the carburetor.
Edit: I need to correct the last bit, this is a brand new engine so the carburetor does not need cleaning. However there are still a couple of things to check. Is your air cleaner sealing properly, not being bypassed by leakage? Reduced air cleaner restriction will make the engine run leaner, as well as letting in dust and ruining the engine. There have been problems at times with ill-fitting ex-factory air cleaners. Also it would be worthwhile checking the external linkage of the governor to see if anything is bent or binding. If possible check the maximum engine speed. I used to do this the hard way, with a stroboscope, but with horizontal-pull recoil starters it was a pain to remove the starter so I could get access to a rotating bit to point the stroboscope at. I've recently started using a cheap plug-lead sensing digital tachometer. It agrees with the stroboscope very accurately, so there's a good chance they are both right.
Last edited by grumpy; 17/05/12 09:04 AM. Reason: Correction and expansion
