New Yamaha 90 four stroke stalls above idle

[TomRay]

Trying to help out a friend here. He just bought new engines for his whale watching boats, and three out of four are fine. One runs fine at slow speeds, but will only run a minute or less at 3k RPM cruise before it stalls and dies.

On other three engines, the bulb in the fuel line behaves normally, but on the problem engine, it stays hard.

These engines are brand new, as are the fuel tanks, filters, and lines. They only have a couple of hours on them. I do not know if they are 2011 or 2012 models, if that makes a difference, but they were purchased last summer.

The boats are in the Dominican Republic and I have better net access up here in Florida, so I'm asking the questions but may not have responses back from the DR right away.

 

[robert graham]

Re: New Yamaha 90 four stroke stalls above idle

Maybe carefully inspect the fuel delivery system from fuel tank pick-up, tank fittings, primer bulb, quick-disconnect on front of motor cowling, fuel pump and fuel filters. It sounds like you may have a fuel restriction or in-leakage of air at a faulty connection or O-ring, or stuck check valve in that primer bulb. Good Luck!

 

[TomRay]

Re: New Yamaha 90 four stroke stalls above idle

Update:

They disconnected and blew out fuel lines inside the cowling and attached the problem engine directly to a 6 gallon tank. It ran fine through 15-20 minutes at various speeds.

They reattached the main tank connection and tested at various speeds for another 15-20 minutes. It ran fine.

Self correcting. My favorite kind of problem.

 

[TomRay]

Re: New Yamaha 90 four stroke stalls above idle

There is a new problem, but I did not start a new thread because it is with the same engine, or at least started that way.

A report last Friday that the problem engine has begun making a squealing noise like a belt on a car might make, but the noise was coming from down low, inside the engine. The engine has also been noted to stall occasionally and smoke on startup on occasion. The engines all have about 100 hours on them at this point.

These are used on a pair of whale swimming boats down on the Silver Bank off the Dominican Republic. The big boat that tows them comes to Puerto Plata once a week, from Friday afternoon until Saturday night. Communications when the boat is not in port are expensive, but possible.

I put my friend in touch with a couple of people to help out when they got back to Puerto Plata and heard nothing more until today. Today he reports that the "problem" engine behaved perfectly while they were back in port, but now they are back out on the Silver Bank and it is acting up again. To make matters worse, one of the engines on the other boat has started doing the same thing. A direct quote from his email today:

The worst of the two makes two sounds: at lower speeds a squealing
fan belt type of sound. At higher speeds (2500 rpm or so and up) it makes a
loud resonant howl.

Can anyone offer a guess as to what is going on with these engines?

A suggestion as to what to do?

Needless to say, there is no authorized Yamaha repair facility in the marina in Puerto Plata. The engines were purchased from a Miami dealership where the sales manager is from the Dominican Republic. We have been in touch with him and he has been as helpful as he can be, but there is a limit to what he can do from Miami.

 

[robert graham]

Re: New Yamaha 90 four stroke stalls above idle

Some of these motors has a rubber Drive Shaft bushing between the power head and the lower unit that can squeal. Unbolt and drop the lower unit to inspect that bushing, which can be lubricated and/or replaced. Good Luck!

 

[TomRay]

Re: New Yamaha 90 four stroke stalls above idle

Thanks, I'll pass that along.