Twin Yamaha 150’s woes

[BigD808]

I have twin 150’s, one of the motors seems to be lagging on the top end, won’t go over 4100rpm WOT, the other revs up to about 5200 WOT. (14x17 Props). So far I’ve changed the high pressure pump filter, fuel, filter, water separators, plug’s. Previous owner did injector cleaning and replaced high pressure pump. Motor has 610 hours. Could this just be that the cable needs to be adjusted? It seems like the one motor is always behind about 2-300 rpm. Idling/in gear pretty much even between the two. Anyone have any suggestions of what it might be?

 

[seasick]

Could be many things. I am not sure what you mean about the one engine running about 300 revs lower than the other. Are you saying that when the throttles are lined up, one motor revs slower? That could be simply a cable that needs adjustment or perhaps a bad cable. To tell, look at the throttle linkage movement with the motor off and the cowling removed. You can uncover both motors and compare each to the other.
Another fairly common cause for loss of top end is a bad coil, injector, plug or even a plug wire. To check, run the engine warmed up to about 1500 revs with the cowling off and pull each plug wire, one at a time to see if the revs change or the sound changes. If you have a bad coil, when that wire is disconnected, there will be no change to revs. Wear gloves and use a pliers of some sort to pull the plug wire off and replace it. Shocks are possible. If there is no change, it could be a fuel issue also. With the motor off, pull the plug and check the electrode. It should not be totally dry. It should be wet with gas. If dry, injector may be bad.

 

[BigD808]

Yes, if the throttles are aligned the starboard motor is running about 300 less rpm through the range. At idle and in gear at idle, they run at about the same rpm (700). I will check adjustments tomorrow, hopefully it’s something simple just as that. If not I will continue troubleshooting with your suggestions.

 

[Pfu]

I have similar situation on my 2000 Yamaha 150’s. going to do a lot of replacing in the spring!

 

[seasick]

I have similar situation on my 2000 Yamaha 150’s. going to do a lot of replacing in the spring!

I wouldn't replace anything unless you have a good idea what the issue is. You can add more variables by replacing parts. The VST is a good example. It is super easy to test top see if the throttle is opening all the way and you don't need two people. That is the first thing I would do.

 

[BigD808]

Throttle cables adjusted on both motors, to spec in Yamaha service manual. I have way better throttle response, but the starboard motor is still running about 800 rpm lower than the counter rotating port motor. I plan on checking fuel pressures and coil’s next. Would anyone know if a damaged prop that was fixed would cause a low RPM issue? I’m curious as the prop on the under performing motor seems suspect to repair. The Skeg on the lower was also sheered off, so I’m assuming the previous owner may have ran into something.

 

[wspitler]

Need more information on your motors. Year, etc. But you may want to do a rigging/sync check and throttle position sensor adjustment. Newer motors are controlled by the throttle position sensor if it’s fuel injected. Throttle cables simply open the butterfly and the TPS controls fuel flow.

 

[BigD808]

Need more information on your motors. Year, etc. But you may want to do a rigging/sync check and throttle position sensor adjustment. Newer motors are controlled by the throttle position sensor if it’s fuel injected. Throttle cables simply open the butterfly and the TPS controls fuel flow.

Motors are 2007 F150 TXR’s

 

[seasick]

Throttle cables adjusted on both motors, to spec in Yamaha service manual. I have way better throttle response, but the starboard motor is still running about 800 rpm lower than the counter rotating port motor. I plan on checking fuel pressures and coil’s next. Would anyone know if a damaged prop that was fixed would cause a low RPM issue? I’m curious as the prop on the under performing motor seems suspect to repair. The Skeg on the lower was also sheered off, so I’m assuming the previous owner may have ran into something.

Loss of top end revs could be a bad prop but could be the other reasons I mentioned. Do the tests I suggested
Without a known good prop it is hard to tell.
The fuel pressure test is also a good idea. You need to look up the spec for your motor and then check yours at speed and load. The fuel rail pressure should not vary very much across the operating loads and revs.

 

[wspitler]

Recommend you get YDIS software and cable $50 on eBay and check all of the parameters, especially TPS voltage and consider getting a maintenance manual and doing a “link and sync.” The TPS sends a signal to the ECM to contro injector fuel flow. The throttle cable only controls air, not fuel. All of the other comments are good, but this software and manual is a good investment at nominal cost.

 

[Pfu]

I like the comment on the software to assist in troubleshooting for novices like me. Ordered mine yesterday!

Are you recommending a third party manual versus the Yamaha manuals themselves?

 

[wspitler]

I like the comment on the software to assist in troubleshooting for novices like me. Ordered mine yesterday!

Are you recommending a third party manual versus the Yamaha manuals themselves?

I like the Yamaha manuals, have had both, but aftermarket are essentially copies. Try to shop around for the most current version.

 

[Aquanut2]

I have twin 150’s, one of the motors seems to be lagging on the top end, won’t go over 4100rpm WOT, the other revs up to about 5200 WOT. (14x17 Props). So far I’ve changed the high pressure pump filter, fuel, filter, water separators, plug’s. Previous owner did injector cleaning and replaced high pressure pump. Motor has 610 hours. Could this just be that the cable needs to be adjusted? It seems like the one motor is always behind about 2-300 rpm. Idling/in gear pretty much even between the two. Anyone have any suggestions of what it might be?

All the things mentioned esp VST are good to check along w measuring pressure on the rail. Also pull your injectors and have them cleaned by a pro they can print out performance before/after mine was down 30% on a few.

 

[BigD808]

Ended up being weak spark, troubleshooting pointing to bad stator.

 

[seasick]

How did you come to that conclusion. Did you remove the flywheel and inspect ot did you run the Yami test steps in the manual?
I am curious .
Thanks

 

[BigD808]

Spark Gap tester one side of spark plug wires to ground on motor. YDS software to ignite coils to see weak spark viewed on spark gap tester. Cross checked spark with good running motor for consistency. Proceeded to check resistance per Yamaha service manual on spark plug wires, coils. They checked out. Moved to voltages from stator via test harness. Voltages we’re low per spec’s on service manual.

 

[seasick]

Good diagnostics. Let us know what the stator looks like when you or the tech accesses it.

 

[232Grady]

If you can see the prop repairs, I would have both props tuned to proper specs. Also, if you take the lower unit off in the future, take it to the prop shop to "fix/fill" the skeg.