Yammie 90 HP kicking my a**

[SCMason]

So I run a boat rental company and we have a Yamaha 90 HP that is kicking my butt. It idles awful and stalls at low RPMS. We have determined that at less than 2500ish RPMS cylinder one is not firing. We changed spark plugs, coil packs, fuel pumps and nothing. We did a compression test and the cylinder was 20 psi lower. When you get above 2500 RPMS it runs like a champ. Im afraid to ask this but could it be the CDI???

Any thoughts and suggestions would help...this motor is driving me nuts and I need the boat back ASAP

[21XDC]

Yamaha has awesome electronics and very rarely do they fail.

[lakefolk]

you need to find out where that 20 psi is going......................

[Les Young]

What about possibly a shift interrupt switch that has gone bad?

[Walkabout7781]

Blown head gasket or broken ring? And, sometimes rings do get installed upside down.

[Fishing Addict]

you need to find out where that 20 psi is going......................

20 PSI seems like quite a bit. Leak down test and probably pulling the head is in order to figure out what’s going on.

[Bassman Ia.]

Blown head gasket or broken ring? And, sometimes rings do get installed upside down.

I’ll go with a broken ring

[SCMason]

Head gasket was blown. We replaced it and had the head milled and flat. What ring are you guys talking about?

[21XDC]

Piston rings