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Rough running Yamaha 9.9 4-stroke

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eric.werkowitz
Captain

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USA
283 Posts

Initially Posted - 09/30/2003 : 23:37:28

I have a 1993 Yamaha that seems to be schizo. At times it runs as smooth as anyone could expect from a 10 year old salt-water outboard. Other times it coughs and sputters and runs only in a narrow RPM range without sounding like it's only hitting on one cylinder. Yet other times it runs smooth, but will spontaneously increase RPMs for about 30 seconds before dropping back down.

I have rebuilt the carb a couple times. Pretty sure blocked jets do not cause the current problems. I suspect the electronic ignition and/or the electric choke. Does anyone have any experience with this engine that might help me to choose the right multi-boat unit part to try replacing first?

Eric Werkowitz
C25 #4969

PS Did you see that Tohatsu is now delivering their new light weight 4-strokes? 85# for a 9.8. They say a 25" shaft will be available in January/February.

Edited by - on

cch
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202 Posts

Response Posted - 10/01/2003 : 08:37:30

Eric,

I have a 93 Yamaha 9.9 as well. Has been a great motor until recently. When we hauled our boat for the last bottom job about a year and a half ago we took the motor to the Yamaha dealer for tune up, oil change etc. After running the motor for a few outings (maybe 4 hours) running time, we developed a problem. The motor would start and run fine for about 15 to 20 minutes then would cut down to about 1/2 to 2/3 rpms. There was nothing we could do to correct this. After about 15 to 20 minutes running at lower rpms it would suddenly come up to normal speed.

The Yamaha dealer suggested a new plastic gas tank, a ring and valve shock treatment and keeping the tank totally full of fresh gas. End of problem. At least we thought. The last time out the problem was back. I have been using the ring and valve additive and a gas supplement although, since we use so little gas the tank is not always totally full.

I have tried everything I can think of (fuel filter, plugs, new fuel line etc.) to no avail. Our boat is out of the water for a swing to wing conversion, so while it is out I am going to try the Yamaha dealer again.

I'll let you know if I come up with anything. Good luck, let me know if you find something.

Chris Hunsicker
Panama City FL
Moonglade
80 C25 #2126 sr/sk
<img src="http://im1.shutterfly.com/procserv/47b3d636b3127cce8c9d4c83e7890000002010" border=0>

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cch
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202 Posts

Response Posted - 10/01/2003 : 08:40:29

Hey Eric,

After posting I realized you are in Niceville. Maybe it is our northwest Florida weather upseting our motors?

Chris Hunsicker
Panama City FL
Moonglade
80 C25 #2126 sr/sk
<img src="http://im1.shutterfly.com/procserv/47b3d636b3127cce8c9d4c83e7890000002010" border=0>

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 10/01/2003 : 08:44:07

Eric,

Before replacing costly components, I would first determine that you have no air leaks in the fuel/carb systems. You mention rebuilding the carb a couple of times...Did you replace the gasket?

<img src="http://www.catalina25-250.org/c25sm.gif" border=0>Don Lucier<img src="http://www.catalina25-250.org/c25sm.gif" border=0>
<img src="http://im1.shutterfly.com/procserv/47b2d904b3127cce9f7cd9ffdf1d0000003010" border=0>
North Star SR/FK

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allencl
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USA
143 Posts

Response Posted - 10/01/2003 : 09:54:51

Guys,

My 87 Yamaha 9.9 FT had very similar symptoms this season- would run perfectly at times, but would spontaneously drop RPMs exactly as Chris described. Three mechanics were consulted (to no avail) prior to replacing the CDI which fixed the problem. The second mechanic said he thought it was the CDI but since he wasn't an authorized Yamaha service guy, recommended that I take the engine to one. The Yamaha folks spent 800 of my dollars screwing around- with no effect on the problem- prior to replacing the CDI which was my written request to them in the first place. Frustrating! But she's back up and running now...

Hope this helps,

-Chris on "SPIRIT" C25 SR WK #5644

Edited by - on

eric.werkowitz
Captain

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USA
283 Posts

Response Posted - 10/01/2003 : 18:45:04

Chris,

Thanks for the info. The CDI was my first guess based on what little info I was able to find on the net. How much did the part set you back?

Other Chris,

I think Chris 1 has the culprit. I'm going to wait a bit and see if anyone pops up with other candidates then I'll order the CDI. And what do you mean "northwest Florida weather?" Was last Sunday great or what?

Eric Werkowitz
C25 #4969

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cch
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Response Posted - 10/01/2003 : 20:50:25

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
I'm going to wait a bit and see if anyone pops up with other candidates then I'll order the CDI. And what do you mean "northwest Florida weather?" Was last Sunday great or what?

Eric Werkowitz
C25 #4969

<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

Eric,

I am not much of a motor mechanic. What is the CDI? You are right Sunday was fantastic. We are in the perfect spot for weather for the next few months. Overall we sure don't have much to complain about do we? How is the sailing in your bays? Haven't made it over your way yet.

Chris Hunsicker
Panama City FL
Moonglade
80 C25 #2126 sr/sk
<img src="http://im1.shutterfly.com/procserv/47b3d636b3127cce8c9d4c83e7890000002010" border=0>

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eric.werkowitz
Captain

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USA
283 Posts

Response Posted - 10/01/2003 : 22:33:23

Chris,

The CDI is the capacitor discharge ignition module. It generates the timing pulse for the ignition coil. If it malfunctions the spark to initiate the firing of the cylinders happens at the wrong time or not at all. The bad news is that I think it costs about $200. Bummer man.

Choctawhatchee Bay is good sailing. I've never been out in the Gulf. Maybe if I can get the outboard to be more trustworthy I'll give it a try and sail over to St. Andrew's Bay!

Eric Werkowitz
C25 #4969

Edited by - on

Gary B.
Admiral

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USA
969 Posts

Response Posted - 10/02/2003 : 02:57:49

I had an early '85 Yammy that finally gave up the ghost by doing what yours sounds like....There was corrosion in oil cooling unit below the power head. The P.O. thought he would fill this "cavity" with marine tex. I never noticed a problem for months after I bought the boat (back; I had owned it before) because I only ran it for 5-10 minutes in and out of the marina. It did not have time to overheat. The first time I ran it for 20 minutes or so it began to shut down the revs, and sound like it was on 1 cylinder, just as you describe. I believe that Yamaha as an automatic "shut-down" feature when the engine oil temp. reaches a certain number of degrees. Since my engine cooling "water cavity" had been filled by the P.O., my only recourse was to buy a new engine in 2000. I love the Yamaha and the new one is GREAT.

I would suggest that you query any good mechanics about the oil cooling feature.....I am certainly no expert on repair options....

The fact that you state that this is a "salt-water engine" makes me very suspicious that I might be correct......

Good luck,

Gary B.
Encore! SK/SR #685

Edited by - Gary B. on 10/02/2003 02:59:57

Edited by - on

Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 10/02/2003 : 03:05:47

The Intermittent Rough Running Yamaha 9.9HP 4-Stroke Problem 

My 1992 Yamaha 9.9HP 4-stroke outboard has had what sounds like the same mysterious symptoms lately. In my case, it seems like one cylinder is firing all the time, but one cylinder is cutting in and out sometimes. The engine seems more likely to run smooth at low throttle, and more likely to run rough and loose power at higher throttle. When the problems occurs, it seems very much like the power is suddenly reduced by half, and then suddenly returns to normal.

Here are some misc. thoughts that I hope will head at least one of us in the right direction. Obviously, if any one solves this, be sure to let the rest of us know what worked.

 Why I have trouble believing it's anywhere in the ignition system. Like many 4-stroke twins with 360-degree firing order, the Yamaha 9.9 uses a single ignition coil to fire both sparkplugs at once. The two sparkplugs are in series with each other. This means that both cylinders share all the same ignition components except the sparkplugs, plug caps, and plug leads coming out of the coil.

 I have tried replacing the sparkplugs, ignition module, and high voltage coil. That seemed to fix it for a while, but the problem came back. I suspect I could have gotten the same temporary cure with just fresh plugs. If you can pin the problem down to one cylinder, you could try swapping plugs, plug caps, and criss-crossing plug wires to see of the problem follows any of those parts to the other cylinder.

 Why I have trouble believing it's anywhere in the fuel system. Again, Like many twins with symmetrical firing order, the Yamaha 9.9 4-stroke uses a single carburetor to feed both cylinders.

But on the other hand... Here's either a long shot or a red herring. If the high speed jet's emulsion tower were clogged, maybe the fuel spray wouldn't be rising high enough in the air stream passing through the venturi to supply an equal fuel/air mixture to both cylinders. If this were the case, I suspect that the lower cylinder would be running richer than the upper cylinder. So, y'all check your plugs while the symptoms are present, and see if the lower plug's insulator cone around the center electrode on the combustion chamber end is darker than the upper plug's firing tip. If you're feeling brave talented and lucky, try getting that high throttle emulsion jet apart and see if it's dirty. If you're feeling more affluent than mechanically inclined, you could try a new carburetor assembly. Let us know what it costs.

 Other long shots to eliminate: So what's not shared in common between both cylinders? Compression. Check your compression as best you can. This can range from seeing if both cylinders blow your thumb off the sparkplug hole about the same, to getting ahold of a professional quality screw-in compression gauge. Either way, be sure the throttle is wide open during all compression testing. (I'd say open the choke too, but I'm 99% certain that these use a bypass enrichener circuit, and so there's no choke butterfly to interfere with air flow.)

Then there's tight, leaking, or mysteriously sticking valves. Do the compression test, check your valve clearances, and while the valve cover is off, see if you can feel whether the valves move freely. Be sure the pistons aren't at DTC to avoid accidentally bending a valve while pushing in open by hand.

I didn't use to consider sticking valves to be all that likely. However, just after dumping some stale boat motor fuel into my lawnmower and mowing the lawn, it wouldn't restart -- no compression. After more troubleshooting than should have been required, I found a stuck valve covered with fuel varnish.

I can't think of any other causes of low compression that could come and go suddenly and randomly. Most of them just come and stay, like a bent valve or blown head gasket. I've never heard of sticky piston rings causing such a sharply defined intermittent change in power output.

I think that's enough wild guessing for one post. <img src=icon_smile.gif border=0 align=middle> This mess will probably need editing anyway.

-- Leon Sisson

Edited for spelling and clarity (maybe).

Edited by - Leon Sisson on 10/02/2003 03:27:49

Edited by - on

cch
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202 Posts

Response Posted - 10/02/2003 : 08:11:51

Hey Guys,

Alot of things to check. I will have my motor in the shop next week and I will discuss all of this with the mechanic. Maybe we can all get rid of this problem.

Thanks for the ideas.

I am off to pick up my new keel at last!!!

Chris Hunsicker
Panama City FL
Moonglade
80 C25 #2126 sr/sk
<img src="http://im1.shutterfly.com/procserv/47b3d636b3127cce8c9d4c83e7890000002010" border=0>

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allencl
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USA
143 Posts

Response Posted - 10/02/2003 : 13:24:40

Eric,

Sorry to take so long to reply. Cost for CDI was just under $200.

Leon- good theories all, I'm sure. I don't know if our engines are showing the same symptoms or not. I will say that fresh plugs did not change the situation for me. Interestingly, the lower plug does tend to run a little darker than the top- but always has in my engine.

When my engine would lose power, it still ran incredibly smoothly. In fact, you could mistake it for running properly if not for the comparison to when it would pick up again- a little louder, more power, faster boat speed. It was as if an invisible crew member was playing with the throttle. This tended to occur most often at the beginning of a run- it might "switch" several times between normal and reduced power within the first 30 minutes and then run perfectly for 12 hours straight. Over a period of several months, the symptom occured more frequently and lasted longer. Eventually, the engine would intermittently run rough and sputter (maybe by then I had fouled a plug) and I no longer felt safe with the situation.

No problems since July 3 when the CDI was replaced. I hope that it isn't just a temporary fix. The Yahama mechanic must have had multiple theories as well because he did rebuild carb, replace thermostat, etc. but judging from the quality of our conversations, I felt he did these by rote rather than thinking through the problem.

Anyway- hope yours gets straightened out. Our symptoms may have different underlying causes, but after my frustration with my own situation I was interested to see that other Yamaha owners are having similar problems.

Regards,

-Chris on "SPIRIT" C25 SR WK #5644

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ksaum
Deckhand

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USA
14 Posts

Response Posted - 10/13/2003 : 21:30:03

I had this problem and the mechanic tried a bunch of things: new plugs, rebuilt the carb, new wiring new gas tank. No change. Then finally it died completly, and a new power pack was needed. This fixed the intermittant power!

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ksaum
Deckhand

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USA
14 Posts

Response Posted - 10/13/2003 : 21:32:16

Sorry, I forgot to sign off---

Ken Saum
Been There C25 #5225

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cch
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Response Posted - 10/13/2003 : 23:45:14

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
Then finally it died completly, and a new power pack was needed. This fixed the intermittant power!
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

Hi Ken,

What is the power pack? How much did it cost to replace?

Chris Hunsicker
Panama City FL
Moonglade
80 C25 #2126 sr/sk
<img src="http://im1.shutterfly.com/procserv/47b3d636b3127cce8c9d4c83e7890000002010" border=0>

Edited by - cch on 10/13/2003 23:46:11

Edited by - on

eric.werkowitz
Captain

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USA
283 Posts

Response Posted - 10/14/2003 : 01:30:43

Chris,

I think Ken means he replaced the motor. At least in a tank or armored personnel carrier, the power pack means a new engine.

I was just going through my Clymer manual for Yamahas and found another suspect part. The pulser coil sits under the flywheel and generates a pulse used to trigger the capacitor discharge ignition (CDI)unit to produce the spark at the plug at the right time. The book says that "...a faulty pulser coil can cause an intermittent or constant ignition misfire." Could be our boy. The good news: it costs $50 which is better than the $200 the other Chris said he paid for the CDI.

There are a couple tests that can be performed on the pulser coil. One is the resistance of the coil which can be done with the engine off, the other one measures the voltage produced while it is running. They should be performable by a reasonably competent mechanic. The Clymer manual, available in many book stores and some auto parts stores, describes how to do the tests.

Eric Werkowitz
C25 #4969

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 10/14/2003 : 09:52:50

A late FWIW... A Yamaha guy once told me the 8hp High Thrust 4-stroke would automatically cut out a cylinder if it overheated. That appears to be a newer design than the 9.9s up to a couple of years ago, but I believe the Hondas (at least the newer ones) do the same. If so, the thermostat could be high on the list of suspects--especially in salt water. I replace it every 2-3 years. Also up there on the list would be whatever sensor is used to detect overheating--it could be a bimetalic switch that might be subject to some corrosion. I'd probably try those before replacing the CDI--the thermostat is a good thing to replace anyway.

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 10/14/2003 : 11:01:29

About a month or so ago, my outboard started to intermittently sputter and miss like it was firing occasionally on just one cylinder. Since this only happened once in awhile and only for a few seconds I put off troubleshooting it until I hauled out this past weekend. When I got the motor home I removed the first plug and inspected it and it looked great. When I removed the spark plug wire boot from the second plug half of the electrode came out with the boot. From the outside the plug looked great (including the firing tip), but the part of the electrode inside the insulator was corroded and apparently broke an inch into the ceramic which resulted in the rough running motor. I replaced the plugs and fired up the motor and so far it’s running smooth.

The moral of this story is…Just because your plugs look good from the outside doesn’t mean that it’s a good plug. With plugs being one of the cheaper and easier things to replace on a motor, they should be changed first when trying to diagnose rough running engines.

<img src="http://www.catalina25-250.org/c25sm.gif" border=0>Don Lucier<img src="http://www.catalina25-250.org/c25sm.gif" border=0>
<img src="http://im1.shutterfly.com/procserv/47b2d904b3127cce9f7cd9ffdf1d0000003010" border=0>
North Star SR/FK

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tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 10/16/2003 : 19:28:35

A similar problem was cured by replacing the fuel pump diaphram. Squeeze the priming bulb a few times, if the revs pick up it's a fuel problem.
Val on the hard DAGNABIT

Val Bisagni]<img src="http://im1.shutterfly.com/procserv/47b3df11b3127cce94709c5ff2e90000000010" border=0>

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eric.werkowitz
Captain

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USA
283 Posts

Response Posted - 10/16/2003 : 20:25:18

The CDI is mounted on the side of the power head just above the ignition coil (the thing the spark plug wires come from). The pulsar coil is under the flywheel which requires a puller to remove. If you buy the Clymer manual for the Yamahas, it steps you through the process.

The manual also describes some tests that can be done that MAY isolate the bad actor.

Eric Werkowitz
C25 #4969

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cfoucht
Deckhand

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USA
19 Posts

Response Posted - 10/16/2003 : 23:33:44

I have a similar problem with my 1989 Yamaha 9.9. After running for several minutes the rpms drop to an idle. Then I can increase the rpms by turning the throttle up. I'm wondering if the CDI can be replaced easily by the owner or is an experienced mechanic required? I hate to spend $200 but I don't want the problem to develop into a motor that won't run when I really need it.
Carl Foucht

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JimB517
Past Commodore

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USA
3285 Posts

Response Posted - 10/17/2003 : 00:12:23

I am sure replacing the CDI is as easy as removing the engine cover, unscrewing a screw or two, unplugging color coded wires, and putting the new one in. A CDI is a classic "black box".

Check the pulsar coil and all the electrical wires for corrosion - especially in a salt water boat. The pulsar provides timing info to the CDI. Any wires that look like green toothpaste need to be cleaned up first.

<img src="http://www.indiscipline.org/cat25/pictures/icon.jpg" border=0>Indiscipline 1978 FK #398

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Dick Johnson
1st Mate

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USA
40 Posts

Response Posted - 10/19/2003 : 11:18:36

Check the oil pump. Mine did that two years ago and it was the oil pump. The motor will shift to a lower rpm when it senses the drop in pressure. It is a built in safety feature.

I had a dealer change the oil pump and it was pricey... Over $300.00.

Richard Johnson

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stephen marcoe
Deckhand

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Response Posted - 11/14/2003 : 11:52:51

rough yamaha problem solved!!!!!!!.if your 9.9 four stroke engine runs smooth with a rpm loss, IT"S the cdi gone BAD..the dealer rebuilt my carb,ran fine for 30 minutes then I rebuilt the carb,which lasted 30 minutes,I played with it for months,by accident as i was testing the spark with one plug out , a spark jumped across to the cdi which for a second made the rpm increase, I was under warranty,and the dealer gave me a cdi no questions asked. I don't know why the dealer is not trouble shooting this problem correctly.the engine ran perfect and never had a problem since

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cch
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Response Posted - 11/22/2003 : 19:00:00

Finally got my Yamaha to the shop, supposedly fixed and back again. The mechanic said There was a combination of bad CDI, thick oil, and overheating due to an impeler getting bad and a partialy clogged cooling line. He said any one of these items would have produced the low rpm condition. All in all repairs cost $424!!!

I can't understand the thick oil as it had been recently changed, I was not aware of any overheating but the CDI seems to be a fairly common fault.

Moonglade will finally go back in the water Thursday or Friday (weather depending)so then I will be able report if the problem is solved.

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