150 two stroke rpm problems

[slosir]

I have a 1990 Yamaha 150 on a 19' proline center console that will only run at 4300 rpm. Did a compression test and had 120 psi on all 6 cylinders and have decent spark across all 6. I think it has a 17pitch prop. Will someone please give me some direction on where to go next?

 

[99yam40]

Re: 150 two stroke rpm problems

Has it ever ran higher RPMs?

Yamaha shop should have a test prop they can run on motor while in tank to see if motor has a problem or if it is set up or prop problem

You can check here to see what a rig like yours ran with what prop
http://www.yamahaoutboards.com/owner-resources/performance-bulletins

 

[slosir]

Re: 150 two stroke rpm problems

I have only had the boat on the water a handful of times and it has never run above 4300 rpms or33mph. I can say that when doing the spark check that a couple of wires knocked the sh@ out of me when the engine was running to verify all cylinders were firing. I found it odd that it was only a could of them did it and not all6