Boat two stroke engine stalls when throttle is applied unless I throttle up very slowly

[sylvaing]

And at one point, power will kick in and the engine will work as usual. If I put more people in the boat, I have to rev up even more slowly before the power kick in. It kicks in at about 2K RPM and revs to about 3K almost instantaneously. It will run fine if I keep the throttle applied. Engine is a 1992 75HP Mercury.

My boat wasn't used at all last year. The year before, I stored it with fuel stabiliser in its 80L tank which was about 1/8 full but when I tried to purge the fuel from it last weekend, it was dry. When I stored it, I disconnected the fuel line and let it starved. I also foamed the cylinders through the spark plug holes.

After putting gas in the tank last weekend, it started easily but when idling, it's running very low RPM and will eventually stall.

Where should I start to try and figure out what's wrong with it?

Thanks

 

[Dave1027]

This behavior usually indicates a lean idle mixture. Try opening the idle mixture screws on the carbs 1/4 turn each. See if that helps.

 

[jimmbo]

Could also be dirt/gum in the Idle Circuit, you can adjust all day but, only leaner, not richer. Another cause could be a Misadjusted Carb-Spark Sync

 

[airshot]

Probably needs carb rebuild with a proper kit. Sitting for a year probably didnt help.

 

[sylvaing]

Hi, I took video to show the behavior

On this one, the first two throttle up was very, very slow and you can see (and hear) that once about 2500 rpm is reached, it revs up to 5000 rpm quickly and I have to slightly drop the throttle to prevent it from over revving. The next two throttle up were quick, I was expected the engine to buck but it didn't. Under load, it will stall.

https://imgur.com/vaPtITp

The next one, I dropped the throttle from 2000 rpm to idle. It almost stalled and if I would have left it there, it would have stalled.

https://imgur.com/Skc1ukC

Not showing here but if I left the engine running at roughly 4000 rpm, after a minute, it will start to drop its speed, almost to a stall, unless I slightly increase the throttle, then it over revs again.

The last one is not related to that problem but I noticed that when revving high in neutral (never checked with the propeller turning so don't know if it's the same), there is water flowing from the bottom of the engine to behind the engine foot. The hose connecting to the exhaust water nozzle (for a lack of a better term) is not leaking and water is flowing well from the nozzle. Not sure if it's normal or a sign of something bad about to happen. Like I said, never noticed it before.

https://imgur.com/TeC8NSm

Thanks,

 

[jimmbo]

Revving in Neutral means Squat. In fact, keep doing it, and you are likely to not have to worry about any Running Issues...
You have had several people suggest things to check, Revving it Neutral wasn't one of them.
Compression
Ignition that can provide a Spark that can jump 3/8" on all cylinders
If the above are fine, and the Timing and Synchronization are fine, then it is time to start tearing into the Fuel System.
As for the water leak, try running the engine with the Cowl off and if there is no Hose that drains there, start looking for a Bad Hose/Fitting, and Leaky Gaskets, or cracks in the Block

 

[909]

Revving in Neutral means Squat. In fact, keep doing it, and you are likely to not have to worry about any Running Issues...
You have had several people suggest things to check, Revving it Neutral wasn't one of them.

Absolutely Brutal Jimmbro I'm dying over here

 

[sylvaing]

Revving in Neutral means Squat. In fact, keep doing it, and you are likely to not have to worry about any Running Issues...
You have had several people suggest things to check, Revving it Neutral wasn't one of them.
Compression
Ignition that can provide a Spark that can jump 3/8" on all cylinders
If the above are fine, and the Timing and Synchronization are fine, then it is time to start tearing into the Fuel System.
As for the water leak, try running the engine with the Cowl off and if there is no Hose that drains there, start looking for a Bad Hose/Fitting, and Leaky Gaskets, or cracks in the Block

Not sure if you watch the same video but you can see I revved up for a few seconds, a few time. I have a hard time believing that will do any damages.

I also posted them because I got three different answers and wanted to pin point the problem.

Although yes, no load and with load are two different things, but I did point out that the behaviour is the same under load, except I have to increase the throttle even slower otherwise it will stall.

For the foot, I gather it's not supposed to be doing that so I'll look more into it. Mind you, it does it under high rpm only so I'll have no choice to run in neutral to figure it out. I'll try to keep that to a minimum. I'm not about to bend over the motor while going at 50+ km/h over water trying to figure out where it leaks

 

[Dave1027]

The video of water coming out of the cowl does not look good. I think you need to find out what's going there. It may just be the tell-tail hose came loose. But you don't want to take a chance on water going into the combustion process. Who know? Maybe the two issues are related?

 

[sylvaing]

The video of water coming out of the cowl does not look good. I think you need to find out what's going there. It may just be the tell-tail hose came loose. But you don't want to take a chance on water going into the combustion process. Who know? Maybe the two issues are related?

Ok, one more video, this one showing where the water is coming out from when running at 1500 rpm. Raising the motor until the the bottom of the lower end is off the water, I can see it's a hole near the base of the foot. I'm guessing it's a overflow from the pump? As I rev up the motor in neutral, I assume it splashes against the engine mounting bracket and flows upward to the base of the motor.

https://imgur.com/a/9KYl67M

Now regarding my engine problem, I added seafoam (15 ml/L) in my gas tank (filled with 5L of premium) the other day. It probably idled about 15 minutes then and revved to 3000 a few minutes (and a few spikes to 5000). After a 30 minutes boat ride today, it seems to run smoother. Four adults in the boat, it still had trouble to move from idle but doesn't stall, just hesitated before revving up. I'll add another 15L with 15ml/L of Seafoam and see how it does when that has been through the fuel system.

One question, can I add Seafoam to the two stroke oil holding tank? Will that help clean the oil injets if needed? Engine is from 1992.

Thanks again

 

[jimmbo]

NO!

 

[sylvaing]

NO!

No to what? To add Seafoam to the oil tank? Because I was just about to post that Seamfoam seems to think otherwise.

https://seafoamworks.com/questions-...o-a-2-cycle-oil-tank-mercury-outboard-solved/

 

[jimmbo]

It is your engine, and if you want to risk it by diluting the Oil...

 

[racerone]

Stop revving this engine !!!----Soon it will come apart by itself.------Learn to do some trouble shooting.

 

[sylvaing]

Indeed. That's why I'm doing some research and asking around. Right now it's starting to run better and don't want to make it worse. One ounce per quart is just 3% dilution but I don't run the boat enough to spend that amount in a decent amount of time and I'm worrying it will degrade the oil as time go by.

 

[sylvaing]

Stop revving this engine !!!----Soon it will come apart by itself.------Learn to do some trouble shooting.

Yes, that's what I've been told. That's why I only revved it a few time for a second or two each to diagnose the problem.

 

[racerone]

Post the compression numbers.----Does spark jump a gap of 3/8" on a test device.----Not a blinking light or on a sparkplug.----Are carburetors confirmed clean ?----Water pump impeller replaced ??

 

[sylvaing]

So far the Seafoam seems to help, I'll see if thing gets better or not. If not, I'll get them.

Today, I was able to cruise a 2000 rpm for about 30 minutes and the engine was running smoothly. I was able to 'punch it' and it went WOT after a slight delay. Only issue I'm currently seeing is I couldn't be pulling someone water skiing as there is too much hesitation leaving idle to WOT. Hoping the Seafoam will keep doing its thing and that will be fixed too.