2023 Yamaha 9.9 high thrust compression reading

[musky/ed]

Wondering if anyone has a shop manual to know what compression reading I should be getting on a almost new Yamaha 9.9 high thrust.
I kept having to turn the idle screw up every couple weeks last summer and finally ran out of adjustment at the end of year. I was taking it to the dealer for some other electronic warranty work and they were going to look at the kicker. While waiting to get in at the dealer I pulled the plugs and they were totally fouled and caked with carbon. As I had a couple weeks yet before my appointment, I got a borescope attachment for my phone and saw the pistons were caked with carbon, as well was the back of the valves.
The dealer ran some commercial carbon clean through for about a half hr, and adjusted in 1/2 turn on the idle circuit, and also supposedly adjusted the float. After that they were able to set the idle speed screw back about to where it was new.
It's winter here but we had a warm spell so I bought a compression gauge to check and only got just under 50 on ea cylinder, also one plug looked good while the top plug was fouled already with only 30 min running.
So I'm sure 50 is a very low reading and feel it should be over 100 but would like to know what is actually recommended in their shop manual as I am pushing them to rebuild it or give me a new replacement. They want to just run another round of decarbonization and I'm not having any of that. Also my bore scope still shows the piston tops still carboned up but the back of the valves are free of carbon now, but the valve edges are bad.
What I would like to know is an actual recommended compression reading.

 

[99yam40]

a complete model number would be good to post when asking about a motor.
Being a 2023 I believe it has to be a 4 stroke motor.
what does the oil look like, and the level?
being new, was it broken in properly.
some motors not broken in properly dilute the oil with fuel and cause it to over fill causing the oil to get into the cylinders which carbon up the valves, pistons, and rings.

 

[boscoe99]

Minimum compression reading is stated as being 91 psi.

 

[musky/ed]

Thanks Boscoe, that's what I was looking for. I knew 50 was way too low. They were trying to get out of it by saying even though readings were low, they were even, so nothing was wrong. They totally wanted to ignore the fact that after cleaning that with 1/2 hr running time, the top plug was black fouled, and soaking wet, and the bottom plug looks like you just took it out of the box. Also wanted to ignore my new borescope pictures that showed the valve edges all cratered and pistons still caked with carbon. I feel the valves & seats are now bad and possibly a stuck ring or two from the original massive carbon buildup. Something caused this kicker to run overly rich when new and they are not looking for the original cause. This was my 3rd Yamaha kicker in 7 years, all used similar, and the 1st two ran flawless.
I really questioned my 50 reading after seeing a youtube of a mechanic getting 110 reading on an older 9.9.
Other facts, yes it's a 4 stroke. I don't know of any 2023 high thrust 2 strokes. The model # T9XPB.
Yes it was broken in right. I did the 1st oil change at about 15-18 hr use as the level had climbed slightly. I then put 45-50 hrs on it and did another oil change, oil level normal. then put another 40 -50 hrs on it before taking to dealer at end of year to be looked at. So it's always had fresh oil and never made oil except the 1st factory fill and I dumped that as soon as I noticed the level starting to rise. I put a lot of hrs on trolling, from walleye to salmon to at times musky. I can put 50 hrs on in a week if my son and I fish a salmon tmt.

 

[racerone]

Perhaps a blown head gasket.----Time for 1-800 YAMAHA help.-----No way that 50 PSI is acceptable.----Or find another dealer.

 

[musky/ed]

That was my thinking with both cyl low, but if that were the case, wouldn't water in the cylinder have cleaned the carbon off? Also my borescope attachment shows the valve edges as bad.
Already called Yamaha, got nowhere, they just said go back to dealer for another carbon clean. Also they said don't worry about the low compression reading. I told them, low was low.

 

[racerone]

Send Yamaha a picture of your newest motor on the boat.----Perhaps a brand X -----But I do not believe they really care too much.-----These companies and dealers today are different than they were in the past.

 

[airshot]

Have you tested your comp gage ?? Some can read erratic.

 

[99yam40]

Since I cannot find a parts diagram for a 2023 motor, I am guessing it is like the 2022 so it has carbs with a choke.

I do not understand how a 4 stroke motor would be carboning up so bad from just gas and no automatic enrichment system to fail and be dumping extra fuel into the motor when not needed.
could the thermostat be bad and not let the motor get up to proper running temp somehow?

is the choke being opened up during running warmed up?

could you have the wrong prop on the motor and it is being loaded up too much

 

[musky/ed]

Just got off the phone with them. They were supposed to call back 1st thing this morning but didn't so I texted their shop manager. It's supposed to snow here Thursday so told him I was dropping the boat off tomorrow so at least the boat was there. Also said I would like a new engine or at the very least rebuild the one I have and if I didn't get a new engine I wouldn't bring the boat home till I checked the compression and scoped it out with my endoscope first after they repair it. He also said my readings were really low and possibly my gauge was off but more that like wasn't that far off to explain how low they were. Especially when you consider my endoscope shows the valves as bad and the pistons still carbon fouled, and also the difference in the plug burning without only a half hr of running after it was supposidly fixed. You should see what the orig plugs and endoscope photo looked like.

 

[musky/ed]

This is a shot of the cylinder when first taking in, you can somewhat see the carbon on the pistons and the scoring on the cyl walls, also the back of the valves were totally caked with carbon.

 

[racerone]

This motor needs to come apart in my opinion.------That scoring is indicating huge issues !!

 

[99yam40]

with that much scoring in that cylinder wall might indicate oil coming up past the rings fouling that one plug.
did the other cylinder wall and piston look OK?

 

[musky/ed]

There was scoring on both but the one with that picture was worse. The black plug was the top cyl. They have agreed to pull it apart as too much looks wrong. Also even with their carbon deep clean, the pistons and head are still caked with carbon, With that scoring and the condition of the valves, and low compression they don't really have much other options as I did tell them I was checking it out before I bring it home. They want to get going on it anyway as in another month and a half they will be swamped with new boat deliveries and people picking up boats in storage there.
I'm done looking at it for now till they tell me its fixed.

 

[musky/ed]

Two last pictures. It almost looks as though there is a low area in the cylinder walls. Almost as though the boring of the liner didn't make it as far as the casting. Notice the amount of carbon still there even after their supposed cleaning. Either that or the rings could be stuck in in that area and it let a build up occur there