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1997 Yamaha 9.9 outboard starting/stalling problem

My 1997 Yamaha 9.9 outboard was running fine. Turned it off for a few minutes and it started hard. The next day it started hard but was ok at idle for a few minutes. Turned it off and tried to start it. Would only start if I gave it full throttle and would stall unless I throttled way up.

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Any stalling/starting problem of an outboard motor may be solved with new spark plug(s).

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Changing the spark plugs is not a bad idea. They are consumable items, designed to be replaced as they wear out, cheap, and easy to do. Why not? BUT if that does not work ...

A common culprit is bad fuel. Two possibilities: water in the fuel, or old fuel that has degraded to a point where it combusts poorly. You wouldn't believe how many truly mysterious symptoms stem from bad fuel. Generally poor quality fuel and the addition of ethanol (attracts water, degrades non-metal parts) make this more and more common. The octane rating (burn-ability) of the fuel goes down as it gets old and eventually it just becomes unusable as fuel.

(There is a third possibility related to fuel, but that involves debris that clogs up the tiny passages in the carburetor. That's a whole different problem that only gets fixed by a) changing out the fuel and the filter and THEN b) cleaning the debris out of the carburetor AKA disassembly/rebuild. Not going into that here!)

I would dump the fuel tank and refill with fresh and see if that solves it. If the carburetor has a little brass drain plug in the bottom of the fuel bowl, take that out, drain the liquid (see what comes out if you can catch it) and refit it. If no plug, just get it running long enough to use up the old fuel and get new fuel through the system.

See if that alone doesn't fix it.

If you have an inquiring mind, when you dump the old gas, pour it into a clear container and see if it separates into water on the bottom and fuel on the top. If it does, you'll be saying, a-HA!

You changed out the fuel and the problem is not solved? If no joy, further and more systematic troubleshooting will be required. I would start by making sure the fuel supply system is not leaking air anywhere between the carburetor and the fuel tank and every hose in-between. I have seen bad primer bulbs (it won't pump up tight like it usually does), loose hose clamps, and bad pickup pipes in the (brand new) gas tank.

The problem is generally either electrical-related or fuel-related. Fuel system problems are easier to troubleshoot first. Determine if the problem is too MUCH fuel or too LITTLE fuel. Here's how:

While running at full throttle (not on the bench, but in the boat and underway), unplug the fuel line. It will run for a minute or so on the fuel in the carb bowl, then run out of gas. BUT: In that 2 seconds before it runs out of gas and quits, if it suddenly runs better as the carb goes dry and the mixture leans out, that is an indicator that the problem is too MUCH fuel. I'd look at the carburetor. Plug in the fuel line, pump up the bulb, restart, and head for home.

But if that trick doesn't make a difference, and while running for home at full throttle again, point a stream of propane gas from an unlit propane torch into the carburetor throat. You are supplying extra fuel for just a moment to the system. If the engine suddenly clears up and runs strong, thats an indicator that the problem is too LITTLE fuel. Go home and investigate that!

If neither of these tricks makes any difference, then you can probably eliminate the fuel system and begin looking at electrical problems. As one poster suggested, changing spark plugs is cheap and easy and sometimes plugs just go bad, so if you didn't do that first, try it now and you may find your solution right there.

After that it gets more complicated. Run the engine in the dark with the cover off and look at the spark plugs, plug wires, and coils. The darker it is the better. Look for anything glowing or sparking ... sometimes old plug wires will allow the "fire"to leak out to ground before it gets to the spark plug, and if that's so, you'll see it.

After this, you'll either need to find more troubleshooting tips or take it to a mechanic. I once had a most baffling problem with a my Yamaha 30hp and got a great tip (the one above about diagnosing too much or too little fuel) from the website http://www.maxrules.com. Click the tab "Technical Assistance" and then "Troubleshooting Tips"and you will find a very systematic diagnostic rundown. If you're still stuck, you can have a paid phone consultation with Bill Kelly, the "MasterTech." I have done this myself and he helped me solve the mystery. Good guy, money well spent.

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first of all you need to check if the water is in the fuel or not. carburetor has the drain plug use flat screw to drain it and see if any greasy or water come out. if you see it, dump all the old fuel and start from there.

make sure you start you engine in the right proceeds: pump the gas to the carburetor (prime bulb) turn the key 1 click to the right (do not start) wait for fews second, and now press the key down for 5-6 seconds so that the "fuel enricher device" sucks the fuel to the engine, wait for 30 second and now start the engine.

if it still not start, try quick start fluid: (don't use it too much if you have 2 stroke engine, because it is not contains oil)

1. if the engine start for the short time and dead (with the quick start fluid), the problem is the carburetor (you need to clean it or even rebuild it).( specially the holes next to the butterfly valve)

2. if with the fluid the engine is not start, you can conclude that because of your ignition is bad (spark plug, wire, coil...) and you need to check the pressure of the engine to see if the piston is not cracked.

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90% of the time this type of issue is due to gunk in your carb, but before you do a carb rebuild (it’s not that hard) remember this.

Rule of thumb, you need compression, spark and fuel to make an engine run.

Most 9.9hp are two cylinders, this procedure works for two and four stroke engines. Take out the spark plugs. Put the spark plugs back in the spark plug boot (make sure they’re in there good and tight) ground the exposed tips of the plugs on a piece of metal (I usually wedge them against one of the bolts) and make sure it stays there, do not touch the spark plug and pull the starter cord and look for spark. If you see whitish blue spark then that’s not the issue.

If you only see spark on one spark plug, swap the plugs. At this point you should trace each the spark plug cord to coil and remember (or mark like I do) which is which, I usually number the coil for the top cylinder 1 and bottom 2. With the plugs swapped to the other boot/coil, make sure they’re grounded and pull the cord again. If you see only one spark and it’s in the same boot/coil (with the other plug) that fired before, then you have a bad plug. If you only see one spark (with the other plug) and it’s in the boot/coil that didn’t fire before then you probably have a bad coil and need to replace that.

Lets assume you have spark in both plugs.

Remove the spark plugs from the boots and put them in your pocket. Press your thumb into one of the spark plug holes and pull the pull start (or ask someone else to) and if you feel a solid puff of air, you have compression. Repeat this with the second spark plug hole. If you feel a good puff of air on both cylinders then you have compression. If you don’t feel a good puff of air with either cylinder (or both) you probably have lost compression and need new rings in the cylinder(s) without compression.

Lets assume you have compression in both cylinders.

Like I said, 90% of the time it’s a fuel issue.

Be prepared to watch a few videos on removing and cleaning the carb, before you do it, I’ve had small Yamaha’s like yours, it’s not that hard to do if you have a few tools (or maybe it’s a good excuse to buy a few?) here’s a good video of a guy cleaning a carb while on the boat! https://youtu.be/LbEM5BNU1Xw

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This is the rule of thumb diagnostic four any small engine, two stroke or four stroke - you need spark, compression and fuel.


Remove plugs, ground them on an engine bolt and pull the starter to check for spark. If there’s spark they’re not the issue. If there’s no spark replace them and test again, if there’s still no spark you probably have failing coils. The coils can be tested with voltmeter, you can look up online how to do that and voltage for your engine, it’s not hard to do.

If there is good spark, remove the plugs and put your finger in each hole on the engine to plug the hole, and pull the starter. If there’s a strong puff of air pushing your finger in each cylinder you have compression. If you feel nothing pushing against your finger you’ve got no/weak compression and need to rebuild and replace rings if it’s a two stroke. If it’s a four stroke engine it may have stuck valves or timing chain skipped a link or two. Either way you’ll need to open up the engine if you have low/no compression.

If there’s spark and compression you’re not getting fuel, and you should clean your carb and probably replace fuel pump.

Outboards I’ve had that behave like yours 80% of the time it’s been the carb and or fuel pump. Usually the fuel pumps are not very expensive so I just replace them with new OEM pump, then take the carb apart and clean it well. Plenty of vids on YouTube how to clean a carb.

I think you’ve got a common issue and pretty easy to fix yourself and know what to do in the future. Good luck!

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