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Just went through a recent carb rebuild and tried to test my Whaler yesterday. This is how my day went;

Outboard started and idled well at the dock, idled through "No Wake Zone" at marina with no issues. Got out on the bay and pushed the throttle, boat came up on plane effortlessly but nose dived a minute later.

Tried to get on plane once again but the outboard would not develop rpm. When I would carefully throttle up the outboard it would begin making a noticeable low growl/rumble as it would try to develop power. It would not develop sufficient rpm's to get on plane. I thought I had spun the prop hub but if that was the case it would over-rev not bog down on rpm's. It idled back to the dock without hesitation put her back on the trailer and home to investigate. Could not find any visible issues so I concluded it might have been the prop.

I replaced the prop last night and made a second attempt this morning. As before, the whaler idled out to the bay with no issues but when I attempted to get on plane the same condition with rpm and engine sound reappeared. Outboard will develop between 2000-2300 rpm's and just loads up not making any real power. Definitely was not a prop problem. Back to the docks, on trailer and home again. NOT A GOOD DAY...

Outboard idles and rev's effortlessly in neutral since carb rebuild, it's only in gear and applying a load that this new condition has appeared. I have already checked fuel supply and feed to outboard. No issues (I tested with a portable 3 gal tank and again with my primary tank alternating between them various times). Have rechecked electrical connections, carburetor "link and sync" and all relevant fuel/oil hose connections just in case, no issues found.

One thing that I noticed yesterday and again today (but didn't give much thought at the time) is when I would shut the outboard off and afterwards (key-on) but (motor-off) my GPS would shut down. It's wired and fused directly to D.C. (Bat.) not through the ignition switch so there's no reason for it to turn off. It has never done that before. The music radio is wired in the same fashion and it too is doing the same thing.

I decided to check the battery just a short while ago with a D.C. Voltage/Load tester and have discovered the battery may be shorted according to the meters readings. I tested the meter with a known good battery to be sure it isn't reading false and it's not. Boat battery appears beyond a recharge at this point.

What I can't understand is how it can still start the outboard, some residual magic amperage or ??? Can this battery condition be the cause of of my outboards sudden power lose at load? The outboard is a 2007 Yamaha 90 2 stroke with just over 97 run hours.

This particular Yamaha 90 outboard does not appears to have a true alternator but a "Stator". Can this stator run the outboards power needs on it own with a compromised battery or does it need the battery to keep a stable voltage? I am a bit rusty with this subject but my feelings are that maybe the "Stator" cannot sustain the electrical system on it's own???

Any and all suggestions will be greatly appreciated. My wife and I will be on vacation all next week and were really looking forward to spending some quality time with our kids and the whaler.

Thanks in advance and I apologize for the lengthy write-up...

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I would go back over what you did on that carb rebuild...sounds like a jet problem. Hate to be the bearer of bad news, but it is much more likely to be something wrong with the rebuild than anything with the electrical system. Put a fresh battery in it from your car and see what happens, if it still does the same thing, you KNOW something's wrong with that rebuild...

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Oh, if it isn't the rebuild that is the problem, it could be that there was actually something else going wrong BEFORE you rebuilt the carbs thinking that the carbs were the problem...Have you consulted a certified Yamaha mechanic?

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Doubt very much the electrical issue is related to your loss of power. You've probably got a piece of lint or something in one of the three carbs, blocking the fuel flow - it was probably floating around in the bowl, allowing you to get on plane the first time, and then got sucked into the high speed jet. I speak from experience, having had the same thing happen to me on a Johnson 70, with exactly the same symptoms resulting. It would idle fine, rev in neutral no problem, but no way was it getting on a plane.

Did you rebuild the carbs yourself? If so, open them up and look for a piece of fuzz or something - it doesn't take much.

Tim

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Before redoing carbs and electrical sytems I would have the motor checked for compression AND vacuum. Two Stroke Engines must have compression above and below the piston rings. Everyone takes engine compression readings from spark plug holes but a lot of people seem to forget that a two stroke engine must have a sealed bottom end that will hold both compression and vacuum.

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It could well be a lack of fuel flow to the carburetor adequate to sustain full power. Has the fuel pump been replaced? It is an inexpensive part. It would not matter what fuel tank was tested because a bad fuel pump is under the cowl.

A bad stator could also cause a loss of power but the loss of power would be manifested by no spark on one or two cylinders.

The odds are far greater that this is a fuel problem rather than an electrical problem, and yes, it could be a clogged jet too.

Needing a new battery could be coincidental to all of this, or you could merely need to thoroughly clean the battery terminals.

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Thanks for the replies. The original problem was carb related, float needle in bottom carb was found to have been stuck in it's seat along with debris in bowl. Outboard would not idle, rpm's would drop and stall O/B.

I took on the carb rebuild myself, I cleaned and inspected each and every removable component for blockage.
I did one carb at a time from tear down to reassembly and am quite comfortable that no contamination got back in. The carb's on these Yamaha's are incredibly simple on the inside, the real issue is the amount of small (and hard to reach) items that have to be removed and disconnected (electrical and mechanical) to get them off.

If they have to come off then so be it but, I want to be sure before deciding by doing the inquiries. So the consensus is that the bad condition of the battery would not affect the outboard when developing a load???

Thanks again to all...

Angel M.

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Just missed your post Tom.

The fuel pump was replaced with carb rebuild. It operates on engine vacuum and have only visually checked for a bad gasket seal at this point. I do see fuel movement through a clear filter in the portable tank's line when connected and running the O/B with it.

From my previous carb issues I am very aware as to how sensitive this motor is to any fuel issues at idle. If there was a newly clogged jet or float needle it would not idle at a steady 800 (factory rpm +/- 50) even with the typical rpm oscillation 2 strokes have.

I am considering visiting and discussing the latest issue with a couple of local Yamaha boat shops guys. I have come across a few different threads discussing pro's and con's of certain AGM / deep cycle batteries as primary engine starting batteries. Found these threads interesting seeing as my current AGM battery is roughly going on 2 years since purchased and is now bad. Tom I did clean the battery terminals and tested the battery yet again with voltage/load tester, it failed again.

I may be mistaken but I still feel this may be an electrical issue.

Thanks again for the replies...

Angel M.

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If a high speed jet is obstructed, it would not affect idle at all - my motor also idled perfectly. I also would have sworn there was no way any foreign material could be inside one of my carbs - I was so careful during the rebuild to have everything perfectly clean. The culprit was a tiny fiber, much smaller in diameter than a human hair and about 1/2" long, stuck in the high speed jet. I have no idea where it came from - could have been just floating in the air when I reassembled that carb. Like I said, it does not take much.

You clearly don't have a problem with the float needle - those symptoms would be completely different, and you would indeed have a problem at idle.

In your situation, I would be flushing out the high speed fuel circuit on all 3 carbs before looking for any electrical gremlins.


Tim

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One way to test it is go to heavy dock and secure the boat and you can similate a load - you can't go wide open but you can let it run a few minutes under load and see if it starves for fuel. As my high school auto shop teacher said during carb rebuild class "they won't go back together wrong, but you can leave s*** out"

If it runs good then sowly conks out you'll know to search the fuel delivery (pump, fuels lines, filter, dip tube, etc...).. If it falls on it's face immediately then you need to look at compression, electrical - or one of the carb circuits. I'm about 50/50 on carb rebuilds anymore - the carb cleaner dip chemicals are much weaker and you are never sure if there are parts that might dissolve.

Good luck with it...

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Thanks again for the replies.

I've decided to have a local Yamaha shop (that I have visited for small purchases and warranty questions) look at it, so happens it is the same shop that rigged the O/B in early 2008 for the previous owner of the Dauntless. The whaler will be dropped off this coming Thursday morning. Other local shops couldn't take it until (and with a big maybe) sometime next week.

I meet with them this afternoon and discussed the outboard's symptoms and what has been done to the motor (by me) thus far. The shop owner was a delight to talk too and offered constructive criticism (about my carb rebuild) along with other possible culprits to the problem.

They will test the outboard with a load and work back from there. I'm not comfortable throwing more money and drive time to the marina in trying to solve this gremlin myself (and possibly hurt the outboard in the process).

The Yamaha is just about at it's first 100 op. hours (98 hours actually) so I'll have them check timing and any other service/mechanical related items that are dealer issues just for piece of mind.

I still have some Summer boating time left (and no Hurricanes on the horizon so far) so I'll bite the bullet and get this resolved properly. At least I gave it my best shot and it may still prove not be a carb issue.

I'll post when repairs are complete and water tested, thanks again to all for the input.

Angel M.

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Your engine has all of the symptoms of a bad stator.

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I have my reservations as well with something electrical. I'll just have to wait an see. The shop owner suggested a simple diagnostic check involving the alarm/buzzer for over heat/ low oil condition.

During both water attempts this weekend I never observed any warning signals or alarm. My Yamaha was setup with a Yamaha digital tach with these features. The shop owner suggested testing the buzzer for a possible malfunction which would set the outboard into a safe mode condition.

Sad to report "No Joy" with alarm it is functioning correctly. So no safe mode condition.


Angel M.

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Well it's Saturday and still no good news to report with my Yamaha 90.

This past Thursday the Dauntless got dropped off at the mechanics. Their preliminary testing showed no issues with electrical nor mechanical. They informed me of this and said that the next tests would be with the outboard being run under load with the prop-dyno.

I went back to the boat shop a while later and they had already concluded the dyno test with no issues or failures to report. The mechanic spoke to me saying that the motor ran strong (up to 5000-5200 rpm's) and the pressures it generated on the dyno were at or better than factory spec's. He could not find any issues with the carburetors as well. The owner (who's a mechanic as well) and the mechanic who worked on my outboard we're stumped with the condition I had experienced the weekend before. The mechanic did drill out the plugs that covered the air-mixture screws to check their adjustment. They were set way to "lean" for the mechanic's liking so he readjusted them to factory settings.

The boat was water tested yesterday on the bay. Once out of the "No Wake" channel I hit the throttle and to my amazement she jumped right up on plane. I got her going at about 4200 rpm's and pushed her a little harder. She was "cook'n" at around 5000 rpm's when just suddenly something didn't feel right, I looked down at the tach and the rpm's had begun to fall. No alarm warnings or buzzers had gone off and the rpm's as occurred last weekend stayed and would not go beyond 2000. I had been on plane for roughly a minute or two when the problem re-occurred.

I immediately called and informed the boat shop on what had occurred. I did a self diagnosis with their instruction while still on the water. That entailed removing the cowling and the air box. I checked for fuel flow from and out-of the emulsion tube visible in the throat of the carb when throttling up, that checked o.k. Next was spraying starter fluid into each carb individually to detect or cause a rise in rpm's if it was a fuel problem, that checked o.k. as well. Final test was while throttling up to slightly cover the carburetor opening (one at a time) to detect a rise in rpm's, no issues could be found. I did check at different intervals the condition of the primer bulb and it was functioning correctly, no collapse or irregular stiffness.

Was not a good day, back to the docks, back on the trailer and onto the boat shop she went. I arrived and spoke to the mechanic and the shop owner on the results of the self-test. Since the motor was still warm the mechanic hooked a water hose to the outboard and started it to better check if a coil or plug wire was the failure. All checked o.k. and he re-inspected the fuel flow coming out of the emulsion tubes at rpm. While in neutral the outboard will rev with no issue at all, it's under load (or while in water) that it's failing.

The carburetors are coming back off but, this time I will be taking them to the mechanic for his inspection and repair if any. The mechanic is not convinced it's the carburetors but, the devil is in the details I guess.

The mystery continues with this Yamaha 90 of mine. Will continue informing on results...

Angel M.

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Something "simple" like fuel line restriction? Vacum created in the tank? We had similar problem one time in a big center console and it was a piece of tape in the full tank that would plug the outlet at speed and then fall off it when we backed off.

Try rigging up a portable fuel tank (shop could do it for you if you are taking it back) and run it on the portable tank.

You know the engine is in good shape. Fuel starvation sounds likely, something not engine related.

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I had the same issue with my Yamaha 70. My guy said it was the carb, then after a cleaning, it ran fine.

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The primary fuel tank was emptied, checked and cleaned. Along with all fuel lines, filter head-mount and connection at motor. The motor was tested with an external fuel tank (at shop) but not on the water, my bad...I forgot to bring my portable tank on the water test.

I'll soon know (Monday) if in fact it is a carburetor issue at the root of this gremlin.

Thanks for the replies.

Angel M.

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If it tested perfect on shop dyno then it has to do with the mount in the boat, either the angle of the engine causes some internal fuel issue when running or the external fuel system has some issue.

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Still sounds like the stator is faiing once it gets heated up. they will do this. Eventually it will go completely, but for now it is testing OK and then failing when it gets hot. I've been there, but with a Merc.

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Wouldn't the stator have overheated during the full load dyno tests?

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You may have already addressed this in post #13 but I had a similar condition with a 115 Yamaha 2-stroke. There are two small heat sensors that insert into small recessed holes in the block. They have a pink and a yellow wire if I recall correctly. and look kind of like a camera battery. If one is bad it is telling the motor it is overheating and will reduce RPMs. Takes seconds to disconnect and it was my problem, also seconds to replace. They do not make the alarm sound.

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It could well be the stator, but it is more common on much older motors and much more common on Mercurys than Yamahas.

I went through this with one of my Mercury 150s. It was running very poorly and the mechanic spent a great deal of time trouble shooting until he finally determined bad stator.

It was not able to generate enough voltage to get the switch box to fire off each cylinder and it was exasperatingly intermittent.

The trouble with replacing a stator preemptively is that it is an expensive part and laborious to replace. Be sure you need to do that first.

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Just happened to find a spare of the part I was describing. Yamaha part #688-82560-10. Wires are pink and black.

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I thought mine was going into some sort of "safe mode" with no alarm. Sounds like yours is doing something similar. It has done it one other time, since the carb was cleaned, and the mech found a loose spark plug wire, but I am still sceptible about that.

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Thanks mtown for the sensor info, I will investigate to see if my Yamaha 90 uses one and mention it to the mechanic.

Mtierney, the coils and spare plug wires have been exhaustively checked (during cold and hot conditions) and we can't replicate the rpm "drop" issue.

Tom, the stator was checked as well but unfortunately it is not displaying a fault that can be detected as of yet. I too have dealt with Mercury stator issues with some old 200 Black Max's that I had on a previous boat some years ago. Hugh pain to diagnose when they are just beginning to go.

Eagles, the fuel delivery set up on my Dauntless is simple and straight forward and has been functioning for the last 3 years effortlessly. The primer bulb that I had installed 3 years ago is what precipitated the carburetor rebuild when it began to degrade internally and send contaminants into the fuel circuit.

I have extensively inspected and cleaned the entire fuel system (twice) for a fault with none found since the original problem began.

I removed the carburetors yesterday and dropped them of with the mechanic this morning for his review. If no issue is found with the carb's the mechanic offered to accompany me one afternoon this week (after carb's are re-installed) for an on-water test. I drained the fuel from each of the carb's float bowls for an inspection but, was very clean and clear.

I'm hoping that the mechanic does find some fault with my carburetor rebuild rather than the problem turning out to be an intermittent electrical glitch.

Angel M.

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And may no longer be functioning effortlessly. Easy to grab a portable tank and hook the engine up directly. An cheap and easy test. The fact the engine was dynoed would seem to elimate all the engine issues like the stator, carburetor crossed wires etc. that would show up with an engine under full load.

I'd certainly check out the fuel system as it does sound like fuel starvation occurs when the flow rate goes up.

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Thanks for the input Eagles. When I get to do the next water test I will certainly bring my portable tank along for the "just in case" senerio.

The "Prop Dyno" test has one flaw that the mechanic made me aware of, the outboard will be run for a brief period of 6 to 8 minutes or the motor will begin to overheat due to water flow or lack there of. 2 or less of those minutes will be at full throttle for generating the pressure/load number. If there is an electrical component issue that fails due to operational heat, the brief "dyno" test will not typically uncover it.

So the jury is still out on wether it's an electrical issue. The mechanic has a suspecion that it maybe a fault within what he refered to as the "C.D.I." control box which sits under the voltage rectifier.