Lack Of Power Under Load

[DAOliveto]

I have a 2006 Yamaha 2-Stroke 50TLR outboard that was giving me intermittent loss of power and appearing to go into limp mode. Now it’s 100% under full load. Will start up every time and idle great. I can briefly throttle up to 3,000 RPM in neutral with no issues, but when in the water under full load it only now gets up to 1,200 RPM’s.

Below are all the items I validated as good, replaced, or rebuilt:

• Removed all gas from the built-in tank and replaced with recreational gas.
• Replaced the primer bulb and secondary downstream gas hose.
• Removed the bowel filter and cleaned (Some minor debris)
• Replaced the gas pump with a new unit.
• Removed all engine side gas lines, inspected visually, and blew out each hose.
• Removed, soaked all three carburetor pieces, rodded out every orifice with appropriate copper wire, and rebuilt with new gasket kit to OEM specifications.
• Warm up heat sensor checks good and operates.
• Water overheat sensor checks good and operates.
• Oil injector float sensor checks good and operates.
• Alarm that operates the two limp mode sensors works, but never comes on.
• New spark plugs.
• New spark plug boots and springs.
• All control rod linkages set to service manual specifications.
• All electrical connects are seated and look good.
• Getting good spark on all three cylinders that will jump a ¾” gap while idling.
• Most ignition components ohm out to OEM specifications.
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• Disconnected the pink wire from the CDI unit under full load with no change. After rebuilding the carburetors and while under load squeezed the primer bulb repeatably with no change to the RPM’s.
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• I’m leaning that the CDI unit (#63D-03) is faulty and not advancing. Don’t have a CDI tester and most local dealers don’t either. New unit $552 and want a second opinion before spending the money.
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• The engine has 670 hours and I’m the third owner with compression readings on all three cylinders is at 110 PSI from OEM stating 122 PSI minimum. Online some boat engine forms say the engine can still run OK with 100 PSI compression. I know this is low, but hoping to get more time out of this motor before rebuilding or replacing it. Head bolts are tight and I can’t see any gasket leaks, feel the compression loss is piston ring related.
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• Bottom line Is this low compression the cause of the loss of power under load? If not, I will procure the new CDI unit as everything else has been exhausted to be the cause of this issue.

 

[99yam40]

110 is good enough.
testing the peak voltages into and out of the CDI will be the best thing to do to tell if one of the components is a problem.
timing light will show if all 3 cylinders are getting spark and if the timing is in spec and advancing properly
draining an in board tank may not get all of the junk out of it, depending on how it was drained and cleaned

 

[FishMan001]

What was the condition of the spark plugs? Were they dry and brown, or black and wet? If they are black and wet, then it's going to be a fuel problem, like either the primestart isn't closing or the small 'O' ring in the choke valve assembly on No.2 carb is shot.
If the plugs are OK, then check the timing is correct at idle and when revving, and that it actually moves when revving (a timing light is the best way).

 

[DAOliveto]

Fleet Admiral, thanks on the 110 is good for now! Had timing light on it at idle and was OEM 7 degrees before TDC, and would advance about 10 degrees after TDC while in neutral and 1,200 + RPMs. Never checked while under load in the water. It's hard to get access to the pickup tube that is mounted under the rear deck. While under full throttle in the water I repeatedly hand pump the primer bulb to see if the RMP's would go up to disprove if I had a blocked tank pickup strainer...no change at all.

 

[DAOliveto]

FishMan001, Because of running the engine at reduced speed at WOT it would cause the new spark plugs to be black and wet. My #2 carb doesn't have a choke valve. I did try while under load to move the manual red control arm from Normal to Open and then to Close with no change to the motor. I didn't have access to a timing light while on the lake and was assuming it was advancing while under load being it would go 10 degrees while in neutral at home. Plugs would clean up somewhat if I just let it idle for 10 - 15 minutes.

 

[DAOliveto]

Fleet Admiral, sorry I stated the wrong idle timing of 7-degrees AFTER TDC (Full retarded) at idle and approximately 10-degrees BEFORE TDC at 1,200 RPM.

 

[FishMan001]

My #2 carb doesn't have a choke valve. I did try while under load to move the manual red control arm from Normal to Open and then to Close with no change to the motor.

The choke valve block is the part of the carb that has the red switch on.
If it doesn't make any difference to the running of the engine when it is switched to open or closed, then I would say it's a fuel issue. Usually, if you switch a running engine to open, it will stall due to excess fuel being introduced.
Things to check for are:
Primestart works correctly (item 33)
Diaphragm not split or holes (item 40)
'O' ring not flat or broken (item 39)
Valve assembly not broken (items 35-38)

 

[DAOliveto]

Thanks FishMan001!

God bless you! People helping people for betterment of all !!!