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Mercury 1998 15hp 2 stroke stalls under load at 1/2 speed

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windswepttom

New member
Hi
My 1998 Mercury 15hp 2 stroke stalls under load at 1/2 speed. It starts easy, and I can rev it up in neutral with no problem which I would think means the high speed jet is OK?

See video of boat tied up to dock revving in neutral and putting it in gear at 1/2 speed at https://www.youtube.com/watch?v=FlHmExFaUrs&feature=youtu.be

Things I tried:
1. Rebuilt carburetor, flush it out with generic carburetor spray, did not soak it in carb cleaner but it revs up in neutral so I think the high speed jet is OK.
2. Adjusted low speed jet
3: Put in new switch box
4. Put in new spark plugs
5. Disconnected both kill switches
6. Changed oil in lower unit.
7. Spun prop in neutral and checked for ease of spin and and clicks and catches
8. New gas and put in seafoam
9. Fuel bulb was hard and squeezing did not help
10. Took boat out for a spin for about 15 min at 1/2 throttle and it worked fine if I did not increase the throttle
11. Did a compression test, both at 90 psi

I put in new coils and stator about 3 years ago.

Any help is much appreciated.

Tom
 
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First off, Do not rev in neutral,parts will go flying! There needs to be a load on her, Run a compression test, Then an open air gap spark test,followed with fuel diagnostics
 
Thanks, OK no more revving in neutral, I did a compression test and both are at 90 psi. If it starts easy, does that not mean I have good spark? I just put in new 90 octane non-ethanol (which I always use), so why do I need to do a fuel diagnostics?
 
Start at the tank pickup tube inside of fuel tank,there could be a small screen at the bottom of that tube,check it, then move forward inspecting all fuel lines,clamps,fittings ETC. How long was your engine sitting? If the carb. was not soaked properly the jets would still be clogged, it needs to be torn down completely and scrubbed, jets reamed carefully to get the job done right, You probably don't need to test the spark, but it can't hurt the troubleshooting process
 
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Thanks, The engine was only sitting one week and I ran it hard. When I cleaned the carb with the can of carb cleaner I spayed all the passages, jets several times with the red tube inserted in each one. But I'll try soaking it over night this time.
 
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windswepttom said:
Thanks, I'll try that, but would it not knock or run ruff in neutral if it was only running on one cylinder?
Click to expand...

No it will run just fine on one cylinder you will just not have any power. Did you put the carb base gasket on correctly it only goes on 1 way.
 
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Almost classic signs of a motor running on one cylinder.---------------We are not there to do the simple no $$ spent checks for you.
 
racerone said:
Almost classic signs of a motor running on one cylinder.---------------We are not there to do the simple no $$ spent checks for you.
Click to expand...

Thanks I'm pretty sure I put the carburetor back together I've done it many times I'll check the spark and both cylinders tomorrow currently the dinghy the davits and back of the sailboat and I'm in Naples
 
The Saga continues
I've been out on the sailboat trying to fix the outboard, now I'm back at the house trying to fix the last issue ( I hope). I had some success.

So I did the live spark test and it was only firing on one cylinder (I was at the beach standing in the water and had a friend pull the starting rope, NOT a good idea, my knuckles were in pain for about 2 hours). Thanks for every one that suggested that.

So I replaced the coil on the cylinder not firing and I had full power and got right up on plane and tested it for about 1/2 hour. Then we went on a dinghy ride for about 45 min with no issues and then it started coughing and sputtering with only 1/2 power, then it would take off on full power for about 5 sec. This went on for about 20 min, and then it ran fine and I got back to the boat. I thought bad fuel so went into a marina and dumped the tank and got all new fuel.

Then I took it for a test and it ran great (problem solved, I thought). We took it for about 1 and 1/2 hour ride. worked great, then the next day it ran great for about 1/2 hour and coughing and sputtered and quit. It was hard to start, got it going with some carb cleaner. Then I readjusted the low speed jet. It worked fine for about 1/2 hour and then repeat of the coughing and sputtered and quit. Hard to start again.

Next morning it starts on first pull, runs for 30 to 45 min and than repeat.

Maybe something heats up and shorts out??? How would I test for something like that?

Any ideas?

Thanks

Tom
 
I made a post this AM, but it didn't take make the forum for some reason, so here is the short version again.

I did the live spark test and found only one cylinder had spark. So I ended up replacing that coil. I had full power and started on first pull.

Thank you everyone for you suggestions.

I tested it for about 1/2 hour then we went on a dinghy ride for about 45 min and it worked great. On the way back it miss-fired and ran about 1/2 power then it would speed up for about 5 sec. It did this for about 20 min. Then it ran fine.

I thought it maybe bad gas, so I took into a marina and they dumped the gas and I put in all new gas. I tested it and it ran fine, started first pull. Went on maybe a 1 and 1/2 hour dinghy trip and it ran great.

Next day it ran great for about 1/2 hour, then miss-fired and quit. It was hard to start, I had to use some carb cleaner to start it. I thought maybe it was too rich, so I readjusted the low speed jet.

I retested it for 30-45 min and it miss-fired and quit. It was hard to start. I let it sit for a few hours and it starter first pull. I repeated this a few more times.

I had the cover off and the fuel bowl/filter was full and the squeeze bulb was hard every time.

Maybe something if heating up and then shorting out???? How would test for something like this?

Anyone have the ohms readings for the stator/trigger?
It is a 1998 I think serial number OG55....

Any ideas?

Thanks
Tom
 
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