Another thing to consider is the vertical link between the gears on the tiller and the magneto. I have seen one that was twisted and would not allow the mag to fully advance. Unlikely but easy to check.
Excellent point indeed… I remember Frank R pointing this out
Many things to consider here. Does everything move easily, not stiff or binding? Something as simple as a wear groove in the roller could be to blame as well. Severely retarded cam pick up setting might be to blame also. David’s suggestion about the vertical rod being twisted should be checked out as well
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