2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

FlyboyTR

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My recent history with Yamaha’s is chronicled in this thread. http://forums.iboats.com/showthread.php?t=525616 It has nothing to do with this problem, other than to give credence that Yamaha’s don’t like me! ;)

The following is LONG, but I wanted to ensure that I included a good history and details so that, hopefully, one of you can guide me in the right direction. …here we go…

I am having an idling and loss of power issue. The motor is a 2003 Yamaha F90TLRB (carburetor). I purchased this engine used two months ago from a dealer (is was on consignment…owner purchased a new lighter weight engine). It had 45 hours on it. The engine is super clean and was maintained by the dealer. After I mounted the engine (pontoon boat) I changed the oil and filter (oil had been drained for transport). I cleaned the “external” fuel tank (it had a 2 stroke mix in it), washed and dried it. Replaced the fuel line, bulb, remote spin-on filter with clear bottom, and new fuel line from the filter directly to the engine filter (which I also cleaned). The tank was filled will fresh 100% gas (no ethanol), and that is what I have used since.

The engine performed excellent with no issues. WOT was 5,600 – 5,700 RPM. I had lowered the idle RPM to 600-700 (at 800 trolling speed was too fast). At approximately 60 hours I had noticed it had a very slight miss at idle while running on the hose. Could not tell it when running in the water. I decided to pull the plugs and take a look.

Plug #1 looked normal. #2 looked like it was running a little warm, but still ok (negative electrode was a little light colored). #3 had a little crusty white ash on it. #4 was similar to #3 but had a white chunk (ash I assume) between the center electrode and body. I replaced the plugs using the recommended plug and gap setting.

The miss at idle (on the hose) was gone and it was much smoother. In the water my WOT was now 6,000 – 6,100 RPM. Fantastic. I used it about 3 hours with a combination of idle, midrange and WOT. No problems. On the next trip out, things changed. It developed a slight miss at idle and on two occasions at near WOT the engine ran rough, slowed down and then returned to normal.

Following this event, I checked the entire fuel system. All the new fuel components only had 15 hours on them. No lines were pinched or occluded. I removed the fuel hose from the internal/engine filter to see if it would free flow. No problems there. I installed a barbed splice and connected a piece of clear tubing between the end of the fuel line and the internal/engine filter (looking for air bubbles). I unplugged the hose from the tank while the engine was running and with a few seconds it had sucked the bulb flat. I let it continue to run until the engine was starving for fuel; no air bubbles were noted in the clear hose. Hooking it back up to the tank, the bulb immediately filled. I removed the piece of clear hose and reconnected everything. I feel confident there are no fuel delivery issues between the tank and the fuel pump.

On the next trip, we had about 45 minutes of fast idle (long No Wake Zone). The next 2 hours were in open water and I pushed her to WOT for a couple of minutes and then backed off to about 5,300 RPM. After about 20 minutes I noticed a slight miss. It continued to get worse. Over the next 1.5 hours the miss was intermittent. Slowing down to a fast idle the miss cleared. Accelerating back to WOT only delivered 5,400 – 5,500 RPM. After a couple of minutes it started missing again and would then sound like it was dropping a cylinder completely. I did the slow down speed up cycle several times. It continued to get worse. I was able to find a spot around 3,500 RPM where it ran fairly smooth, with ONLY an occasional miss. We arrived back at the boat ramp.

When I cranked the engine to put the boat on the trailer, it was very difficult to start. Back home, on the hose, it idled very rough.

This morning I removed the plugs and much to my dismay, I found a mess. #1 was normal. #2 looked like it was running a little warm. #3 was covered in thick crusty white ash. #4 was similar to #3 but the gap between the center electrode and the plug body will filled with the ash. Please see pictures. I went back through the fuel system, visually, and still feel certain that I do not have a fuel delivery problem to the fuel pump. I also unbolted the fuel pump and squeezed the bulb hard to see if I had fuel leakage on the back side (possible diaphragm issue). No problems there, reinstalled the pump.

I have seen a lot of “hot” plugs from a slight run-lean condition, but honestly I don’t have a clue about all this white ash! My next step is to pull the carbs and clean them. The next step, after that, is a bullet. Someone is going to have to shoot me or the motor…because one of needs some relief!:eek:

I welcome your ASAP input, suggestions and questions. Thanks!
 

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99yam40

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

Excessive fuel additives or oil will cause the ash build up.
How and with what did you wash the tank out with?
are using the proper oil?
Is it using oil?

Of course not all plugs are having the problem so, might look at rings of valve guides.

Cleaning carbs would be one of the 1st things I would have do, just to eliminate that
 

FlyboyTR

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

Excessive fuel additives or oil will cause the ash build up.
How and with what did you wash the tank out with?
are using the proper oil?
Is it using oil?

Of course not all plugs are having the problem so, might look at rings of valve guides.

Cleaning carbs would be one of the 1st things I would have do, just to eliminate that

No fuel additives. Tank was washed with soap and water, then dried. Yes, correct oil and it not using oil. Thanks for the input.
 

FlyboyTR

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

UPDATE:
I started with the #4 carb (since it was the worse cylinder), pulled the bowl and tiny inlet filter. Clean as a pin. I stopped, and put the bowl back on. Checked the compression. 128 on 1 & 2. 105 on 3 & 4. I then did a tongue test on the spark plugs. 3 & 4 both tasted salty. The last trip was in salt water. I am hoping that it is just a head gasket. I have placed a call to my yamaha mechanic. I will put it in his hands on Monday. I will post an update on his findings, etc. Thanks!
 

99yam40

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

Used motors are a gamble even if you can run them first, but a lot worse if you cannot.

So you are saying that build up is salt not ash?

4 strokes tend to have a lot more compression than 2 strokes and even 128 psi sounds like a real low #.
Leak down will say more on a motor. But that is not the issue right now, or maybe it is if all the cylinders have a problem and not just 3&4

Did the oil look OK
 

FlyboyTR

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

Used motors are a gamble even if you can run them first, but a lot worse if you cannot.

So you are saying that build up is salt not ash?

4 strokes tend to have a lot more compression than 2 strokes and even 128 psi sounds like a real low #.
Leak down will say more on a motor. But that is not the issue right now, or maybe it is if all the cylinders have a problem and not just 3&4

Did the oil look OK

Yes. Based on the fact that it is like sticking your tongue in salt! ...so not ash. The oil is fine and looks just like it did before the last outing.

You’re right, used motors are a gamble. When we bought the boat it had a 2006 Yamaha 50 two stroke. I bought it knowing it would not run. It would hit a few times and that was it. I figured...easy fix, clean the stopped up carbs (had been sitting for 8 months and I had opened the carb drain and it was nasty). Wrong! Turned out the top and middle crankshaft bearings had frozen, spun and spit out the bearings. They also took out two pistons. So, new crank, pistons, etc. Still wouldn't run right...very rough idle. CDI box was bad. After I replaced the box, it ran fine...but I was "done" with it and sold it. I lost some $$$ and was ready for it to go.

I put the word out to a number of dealers that I was looking for a 90 two stroke (a nice upgrade in HP). Several weeks later I was contacted by a dealer that had one he had taken on trade. He wanted to sell it "as is." I pushed and he gave me a 30 day warranty. It never ran right. Terrible idle, missing at higher RPM’s and would sometimes drop a cylinder completely for 10 -20 seconds. In and out of the shop numerous times. I finally checked the plugs myself and found white foamy goo. Turns out it had a hole in the block! ...sort of makes you wonder about those factory trained mechanics! He ended up doing the right thing and gave me my money back. The next step is motor #3... the subject of this tread. UNBELIEVABLE …

And no! That is not the mechanic that will be working on this problem! :)
 

99yam40

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

What about the compression?
How took it and did it get done?
If the butterflies are not cracked open the readings may not be what they should be
 

FlyboyTR

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

What about the compression?
How took it and did it get done?
If the butterflies are not cracked open the readings may not be what they should be

See post # 4 for the compression readings. I had the carbs off when I did the compression test. You're right. Many folks do a comp test with the throttle at idle. I always open it up, kill the ignition and crank away! :)

OH... My tester would not thread into the spark plug hole (too short). The threads are recessed about 1/2" in from where the plus seats. I took one of the original plugs, cut off the top, chucked it up and drilled it out. Then I TIGed an old adapter to it so the tester would thread in. By the time all that was done... I was at my wits-end... and wanted/needed a beverage.

And speaking of such... Thanks again!
 

99yam40

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

looks like I had one too many myself from what I wrote "How took it and did it get done?"

I meant to say who took it and how did it get done.

But you understood and answered my questions.
Still think 128 is too low for a 4 stroke, but maybe some thing to do with your tester.
Keep us informed of what you come up with
 

FlyboyTR

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

looks like I had one too many myself from what I wrote "How took it and did it get done?"

I meant to say who took it and how did it get done.

But you understood and answered my questions.
Still think 128 is too low for a 4 stroke, but maybe some thing to do with your tester.
Keep us informed of what you come up with

LOL... No problem! It is possible that I may have had a pin-hole or two in the compression tester adapter when I welded it together... causing a low reading on the good cylinders. Thanks again!
 

mommicked

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

I'm no expert but those plugs look very greasy on the threads. Are you applying too much antisieze to the threads? do you use ringfree or other additives or ethanol fuel?
 

FlyboyTR

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

I'm no expert but those plugs look very greasy on the threads. Are you applying too much antisieze to the threads? do you use ringfree or other additives or ethanol fuel?
The antisieze I use is black so it doesn't hide as well as the silver stuff! No, not using too much. I've never used Ringfree or any other additives or ethanol fuel in this engine since I've owned it. I can't say what the previous owner did.
 

FlyboyTR

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

UPDATE:
My mechanic arrived this morning to start troubleshooting and repair on our Yamaha F90 outboard motor. He pulled the head. There was nothing obvious regarding the head gasket or mating surfaces. We all took turns looking for a water track, leakage, etc, etc. Nothing. Pulled the exhaust. Same thing... Nothing. He removed the rest of the engine (block) and will do a thorough inspection back in his shop.

Scott said the next step if he can't find anything will be to call Yamaha.

Since there was a definite issue with the compression on the bottom two cylinders, I was really expecting to find a blown head gasket...or at least something that was relatively obvious.

The saga continues. I really need a cold beverage and something greasy to eat...and some chocolate too! ...sigh...
 

99yam40

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

Did he do a leak down test or compression test himself before opening it up?
I always do some testing myself on a motor before tearing it apart, not necessarily that I do not believe what someone else tells me, but then I can be sure of what the testes really say just in case there was a problem with others equipment or technique
 

FlyboyTR

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Re: 2003 Yamaha F90-TLRB: Engine Missing and Loss of Power

Did he do a leak down test or compression test himself before opening it up?
I always do some testing myself on a motor before tearing it apart, not necessarily that I do not believe what someone else tells me, but then I can be sure of what the testes really say just in case there was a problem with others equipment or technique

Yes he did. Actuall came up with the same numbers I had (+ or - a couple of PSI). I failed to mention it in my last post... the combustion chambers and exhaust manifold for #1 & 2 also had minor traces of salt crystals...getting progressively worse going down.

I will be on a snow ski/snowboard trip next week. So I will report and update with what I have when I return. Thanks again for the concern and the valuable input! ...appreciated!
 
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