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help, 1990 yamaha 40SD 3 cylinder

paulp1014

New member
I have a 1990 yamaha 40hp 3 cylinder (40SD model number) it is only running on 1 cylinder. I have cleaned all 3 carbs. replaced all plugs, cleaned/swapped reed valves, and have compression @105 psi on all 3 cylinders.I have also swapped plugs wires to check if it could be those but they all work on the good cylinder I know it is only running on one cylinder b/c I have taken spark plug wires off the top and bottom plugs and there is no change in in engine performance. I am truly at a loss for what could be causing this. I have spark, compression and fuel. This is not a trick question this is really happening. if anyone can help I would greatly appreciate it.
 
You will likely get more help if you post this on the Yamaha Forum on this site. Got to top left of this page. Click on "Forum Home" then scroll down to Outboard Motors, then click on Yamaha." Start a new thread on that forum.
 
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