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1997 merc 9.9 2 stroke wont run under load

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OntarioKyle

New member
Hello all. Frequent visitor but first time poster on this forum. I cant find any other issues that match my exact issue, so I will outline it below.

after winter storage, my 9.9 2 stroke fired right up after one pull. after a warm up idle, i took off and for about 2 seconds, the motor made power fine. then it died down as if starving for fuel. for the remainder of the day, the only way I could get around was 1/4 throttle and a bit of choke. without choke, it idle fine but dies as soon as I try to put power down. after it quits. It always fires right back up easily.
I would like to add: priming the fuel line (pumping the ball) does not help, and the fuel pump diaphragm is in good shape. I have inspected the lines and tank for air leaks but haven't found any yet. Main jet and pilot jet were cleaned thoroughly. Carb was drained and motor fogged before storage. fresh fuel at the beginning of the outing. I believe it is a carb issue because it will not die or sputter when being choked, only without choke.
problem is intermittent. Every now and then I can get 30 seconds of good performance before it starts to die again.
I would like to add that the cooling system is working well, and hot water fires out the back of the motor while running. Would also like to add that the bottom end oil is also brand new and was put in 25 min before launching the boat, so its not the bottom end seizing up.

I looked at the float and when the carb is held upside down, there is about a 1/4'' gap between the bowl mount flange on the carb and the top of the float. i have looked and looked, but can not find factory spec for float height setting, so I'm not sure whether float height is to blame,

I have yet to try sea foam and am going to clean the carburetor again. other than than, I am at a loss on what to try, the motor ran awesome last time it was used (last November) .If anyone has any clue what to try/check, please let me know. It theres any more information I can add, or anything you need clarified, let me know.

Thanks in advance.
 
I would also like to add, i can rev the motor out in reverse as much as I want and it will not die. that combined with the fact that it runs all day with the choke half way on leads me to believe it cant be electrical, however I have been wondering if the problem could perhaps be the CDI Box
 
Check for spark with a spark checker should jump a 7/16" gap. It could be the switchbox go to www. cdielectronics.com they have the testing procedures for your ignition. Running in reverse means nothing it is like revving in neutral. The reason is the prop cavitates in reverse if you rev it to high it is basically running in air.
 
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flyingscott said:
Check for spark with a spark checker should jump a 7/16" gap. It could be the switchbox go to www. cdielectronics.com they have the testing procedures for your ignition. Running in reverse means nothing it is like revving in neutral. The reason is the prop cavitates in reverse if you rev it to high it is basically running in air.
Click to expand...

why would the motor run fine with the choke on if its an electrical issue? not that I am doubting you, I just want to know the logic behind it.
 
I say check spark because it is a good thing to do. The carb probably needs to be soaked and rebuilt with a quality kit. Another reason to check spark is because of the 30 seconds of run time then kicks back out.
 
Sounds like something was missed in the carburetor work.----Also run with a timing light to see if anything shows up as far as ignition problems with the " instant improvement " in performance.--------Have you checked for water in your fuel ?----Sorry,----You have to turn the wrenches on your motor.----We can not inspect for you !
 
racerone said:
Sounds like something was missed in the carburetor work.----Also run with a timing light to see if anything shows up as far as ignition problems with the " instant improvement " in performance.--------Have you checked for water in your fuel ?----Sorry,----You have to turn the wrenches on your motor.----We can not inspect for you !
Click to expand...

I have been turning wrenches on the motor for the last two weekends. I'm looking for advice on what the problem may be based on what i've explained. and again, like I said in the original post, if theres any other questions I can answer that may clear things up, let me know.
I have not done much in the way of checking timing or spark. I actually ruled out electrical problems due to the fact that I can run it all day long with the choke half way out. i'll replace plugs and check out the ignition system while im at it, but im pretty much convinced it is carb related.

I havent checked for water in my fuel, but I ran 89 (mid grade) in it. it was brand new fuel so I cant imagine the water wouldve separated from the fuel that quickly. tank was filled up an hour before I ran the motor and encountered the problem.

I'm wondering if its possible the carb float level is set too low, but that would cause it to sputter out at high rev in neutral and reverse, so I would think.
 
Your motor has a primer not a choke. By running it 1/2 out you are bypassing the carb circuits. How many turns out is the low speed mix screw? Is the carb base gasket on correctly it only goes on one way?
 
flyingscott said:
Your motor has a primer not a choke. By running it 1/2 out you are bypassing the carb circuits. How many turns out is the low speed mix screw? Is the carb base gasket on correctly it only goes on one way?
Click to expand...

actually, it has a choke AND a primer. (primer puller has a choke plate linkage attached to it, and when choke is pulled all the way out, it it hits a primer on the carb) you are correct though, I am bypassing the main carb circuits by choking it, which is what leads me to suspect fuel pump, timing and spark is good. I have yet to check the number of turns out the low speed mix screw is. motor runs mint in a barrell in the driveway, only has problems on the water, which makes it difficult to adjust stuff like that. ill be bringing some tools with me on the water next time.
 
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I have never seen a choke flapper on one of those. If it is a remote model it has the mechanical primer off of the knob and the electric one mounted to the top of the carb.
 
not sure what is meant by remote model. it is a tiller drive if thats what you mean. as for choke, it has a mechanical primer, and the same knob you pull for the mechanical primer on the carb has a link attached to what appears to be a choke mechanism on the side of the carb.
I only have to pull the knob a quarter inch, not enough to hit the primer plunger, just enough to pull (what I believe to be) the choke link a bit, and it will run fine (albeit, rich).

I was doing some thinking... the fuel gauge on my fuel tank had an issue with leaking right by the fitting for the fuel line on the fuel tank. I seem to recall noticing a couple bubbles of gasoline around the previous repair job (silicone) and am wondering if perhaps it is sucking air from there. the primer bulb did feel a little soft, like there was air in it. could this explain why choking the motor makes it run? pulls fuel a little harder due to the added negative pressure inside the carb?

only flaw there is that I would think it would sputter in neutral in reverse in that case too.
 
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That is not a choke. When you pull it forward like that it either pulls the throttle open or advances the timing for your high idle. What it does depends on which ignition system you have but you do not have a choke. The fuel sender should have nothing to do with the fuel pick-up in the tank. The bulb will go soft after it runs thats normal. Now if the bulb stays soft when you are first priming it that is a carb issue with the float and needle. I would clean and rebuild the carb with a quality kit that includes the fuel pump and primer diaphragms. You need to answer this is the carb base gasket on correctly? If it is on backwards it will cover the fuel pump pulse port.
 
thank you for that information, I was not aware it wasnt a choke. so sucking in air at the connection between the fuel tank and fuel line wouldnt cause an issue? IO seem to remember specifically feeling air in the bulb while the motor was running. but then I still dont see how pulling the primer knob would fix this to the point that the motor runs properly again.

the bulb, from what I remember, stays soft no matter how much I prime it. as for carb base gasket, do you mean the one between the float bowl and the carburetor body? if so, I believe it is, but wont know until I see it in front of me friday evening. I will definitely check. perhaps you are right, I may start looking into a full rebuild kit.
 
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If your bulb stays soft and never gets firm then you have a float and needle issue. The base gasket I am talking about is between the block and the carb. Look at the wire from the primer knob if it goes under the flywheel it adjusts the timing. If it is a short wire and goes the carb it adjusts the throttle those are for cold starting. That will have nothing to do with your running issues. Maybe your best bet is see if Racerone is near you and take it to him. I gave you a place to start ,it is time to go outside and work on your motor or take it in.
 
trust me, ive worked on it a bunch already. im close to taking it in, but want to make sure ive checked everything first. i suspect the float level could be wrong. i think i've found the factory spec for the float height so ill check it next time I get the chance. cheers.
 
Many possibilities as mentioned in the above posts are valid, and suspects to be investigated, but I suspect it is a carb issue, you say you have cleaned the jets , but, was the cleaning successful. also, especially with pilot jets, the jet leads usually to a drilling, the actual jet just being the device to deliver the correct quantity of fuel. The drilling in the carb body is just as susceptible to obstruction but only by things smaller than jet size, old fuel gunge and debris, if blocked your starting would not be so easy, but partial ’floating‘ obstruction which ‘settles’ enabling the easy start, but moves under increased fuel flow and vibration fits the clues you give, the total fuel delivered is pilot plus main fuel quantities, on the increase demand for fuel and a floating blockage the mixture becomes weak and the motor appears ‘starved’ and won’t rev higher than the fuel squeezing through will allow, …. along with too much air from an open throttle for the amount of fuel delivered, perhaps kill the engine whilst it struggles and look for white spark plug electrodes.

With carb cleaning I find the can of WD40 and straw helps, not in the actual cleaning, but to be able to see a good squirt of fluid making its way through the jets and drillings through to the bore of the carb. Better than just blowing compressor air through and assuming the job is finished.

I confess to knowing absolutely nothing about your actual engine and carb, but 40 years running vintage motorcycles with awful carbs teaches one a few things, and the physics of carburettors doesn’t differ on a boat.
Hope the above is food for thought in your diagnoses, and you find the cause.
you might consider ultrasound cleaning of the carb body …….. followed by a squirt of WD.

(Yes I realise it’s an old thread, but the subject is of interest to a new 9.9 2 stroke owner)

CB
 
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