2004 Yamaha OX66 SS - No power over 4000 RPMS

[Todd UNF]

I have been working on my boat over the winter and the first time I took it out it didn't run that great. It will not go over 4000 rpms and it sometimes stumbles while cruising. Feels like a fuel problem to me. I have used another tank to isolate my fuel and no change. It is real close to 4000 RPMs so I was thinking the engine has a safety like the oil safety at 2000 RPMS. I put new plugs in last week as well. I took out last weekend and it runs exactly the same... Any ideas? I am ordering new LP fuel pumps tomorrow as well as fuel filters (installed new Racor in boat last week - no difference). Computer issue maybe??
Thanks in advance for any help.

 

[99yam40]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

Always give full model # and what you have done to motor. It helps others to see some history of what has been going on.

check compression, timing, and spark.
Test fuel pressure and vacuum to make sure fuel supply system is functioning properly and has no restrictions or sucking air

 

[Todd UNF]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

The model number is SX200TXRC. I actually rebuilt the engine and had only been able to run the engine on a hose. No knocking or any "internal" engine sounds, just a little rough idle and reduced power. I'm stumped now...

 

[99yam40]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

Why did you rebuild the motor?
Was it because of piston/cylinder damage from lean fuel, and did you fix what caused the damage?
If not you will be doing it all over again

 

[SparkieBoat]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

you need to find your problem or 99 will be correct. test your fuel pumps before replacing them..get a manual and find your problem. it could be many things..all filters should be replaced yearly.

 

[Todd UNF]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

My problem was the oil transfer pump. I was having issues and the alarm went off a couple of times and I would add oil and a few trips later I was coming off a plane and the motor shut off(no alarms). Cranked back up with a knock so I checked the engine mounted tank and it was almost empty. Corrected issue after rebuilding by replacing the entire oil transfer system (tank,filter, pump, harness). It is a new issue that is causing this problem. Does anyone know of a error condition that the computer limit RPMs to 4000? It seems odd to me that it would do it at the same rpm every time if it was a fuel issue.
Thanks

 

[ski racer]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

Hi, I have 2002 yamaha 250 ox66, i am having exactly the same problem, no more than 4000 rpms. have been trying to get to the bottom of this problem for over a year! Havent solved it yet but will let you know what we've done so far. Have changed all filters, changed the T.P.I, changed the o2 sensor, changed the plugs, had all the injectors proffesionaly checked (all good), checked the fuel pressure whilst under load (35 psi), changed all the lift pumps, changed the main fuel pump, changed the filter on the fuel pressure regulator (easy to miss) and running a new fuel tank.
None of this has helped it still pulls away a bit flat and wont rev passed 4000.
have spoken to a specialist in sandiago, he's said now to try changing the thermostats on the top of the cylinder heads, if these are faulty they will flood the cylinders and make the motor run flat. we're going to try this next, Ill let you know if that helps

 

[Big flop]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

Have you checked the filter in the VST tank?
All power reduction limiting at 2000 RPM or lower.
As far as thermostats sounds pretty thin?

 

[99yam40]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

Ski,
Start your own thread

Todd,
What did you find when you opened up the motor? bearings or pistons problems?
Almost empty does not mean ran out of oil.

Sounds like you have a fuel issue and that may have been your problem last time also

 

[ski racer]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

read my reply, im trying to help todd
The point is no more than 4000 rpm is a specific problem. One I now know a lot about as you can tell by the amount of wasted time and money ive spent.

According to Robby Gorden from Boating dynamics, If the thermostats are malfunctioning in any way it will tell the engine to run full rich, out come being 3800-4000 rpms

 

[99yam40]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

ski,
I reread you post and it still sounds like you are asking for help, but that is beside the point if you say you are just trying to help him out.
But he and you need to test things and not start replaceing things to see it it will help.
It the thermostats stick closed or not open all the way the motor will overheat and alarm.
is they stick open, which does not happen very often,then it could cause some motors to run too cold which would make the motor think it is still in warn up mode and have a high idle and run rich.
On some motors some sensor failures will cause this also.

I would recommend getting the proper equipment to test these motors or take it to some one that does to find out what is going on.

There are some system failures that could cause the motor to run too lean above 4k and will pop pistons if run that way

Sometimes you can tell what is going on from what the timing is doing, but the motor should throw some codes if it is having problems

 

[SparkieBoat]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

it is easy to eliminate t-stats by checking your operating temps. As 99 said you will need to test each component of your motor until you find the problem. there are specific test and settings for most parts. It just does not take much to throw it all out of whack. Todd, exactly what was damaged in your motor when you rebuilt it?? it may or may not have any bearing on your current problem. But just changing parts is not the best way to go...can get very costly with little results.

 

[m14918]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

I have been working on my boat over the winter and the first time I took it out it didn't run that great. It will not go over 4000 rpms and it sometimes stumbles while cruising. Feels like a fuel problem to me. I have used another tank to isolate my fuel and no change. It is real close to 4000 RPMs so I was thinking the engine has a safety like the oil safety at 2000 RPMS. I put new plugs in last week as well. I took out last weekend and it runs exactly the same... Any ideas? I am ordering new LP fuel pumps tomorrow as well as fuel filters (installed new Racor in boat last week - no difference). Computer issue maybe??
Thanks in advance for any help.

I have a1995 Yamaha 200 that does almost the same thing. Ran fine at low idle and at 3000 rpm started vibrating and shaking then stalled and I had to be towed in. If you have any suggestions, I would appreciate it as haphazzardly changing parts is often useless and expensive. Max rpm I could achieve was 4000 then boat would lose rpm and stall even though I had throttle forward. I just don't trust this motor anymore on the ocean. have it on a Aquasport 222 sandpiper.

 

[99yam40]

Re: 2004 Yamaha OX66 SS - No power over 4000 RPMS

1st thing I would recommend would be to start a thread on your motor and problems.
secondly I would say to test things like we told the others