im confused

hey guys i just finished my 12 foot tin "slammin salmon" i got a 1981 johnson 15 hp on it, i rebuilt the carb, fuel pump, new impeller, new lower unit that i rebuilt, new gear oil, fresh gas mixed 50:1. i went for a shake down run this morning to see how she does the first time, since the time i got the motor dialed in, running on muffs, it runs beautiful first pull every time, idles perfect, revs with no problem, i kept the revs low so i dont mess it up, i got the dreaded "runs on muffs but not in water" syndrome, i get to the ramp at 5am dipped it in the water primed it first pull it starts and stalls instantly. Took about 10, 15 pulls to get it to finally fire and idle, i warmed it up on the trailer while i unstrapped it and got it ready, i idle to the dock went into gear without stalling, i go to take off after warm up, it just bogs when i give it throttle, wont go past much over idle before just stalling, fires back up first pull, neutral rev same thing wont go past much more than idle before bog and die, got it back to the trailer strapped it in while still submerged and started to engage the prop and running it while i can stand and mess with it, i work the choke and was able to get wot with it with some bogging before getting there, long story short same thing happened after i went for round 2 this time it wouldnt start back up. i called it a day and took it home. about an hour ago i put the engine in a 55 gallon drum full of water with the hose on keeping it full, fired first pull with no prime and no problems, idled perfect let it warm up for 5 minutes and engaged the prop and started to run it, went through idle to wot and held it for a few seconds and repeated it with absolutely no bog. lower unit completely submerged to create the back pressure as it would be on the lake, had no issues whatsoever. does running in a barrel simulate it running on the lake? Why would it not run earlier for anything but suddenly 15 hours later it ran perfect in a barrel? could i have flooded it earlier by over priming possibly and fouling the plugs and it sitting dried them out enough to run again? sorry for the long post im just confused and irritated after all the work ive done on my boat. thank you so much for any advice and help and for your time

pussiwillow said:

could i have flooded it earlier by over priming possibly and fouling the plugs and it sitting dried them out enough to run again?

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possibly. but not likely. the fuel will evaporate but not the 2t oil. next time it happens again try to check the plugs while you're at the ramp.

i work the choke and was able to get wot

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have you checked if the A/F screw is set correctly?


i have to admit, running in the bucket and not running in the lake is a mystery to me. i hope the guys here can help you.

You have an air leak in your fuel system - either the line, bulb or gas tank has a bad fitting


I had the same problem and was able to fix it once I tighten some fuel line fittings

Try a new line and new tank and I bet you it will run fine

my sea king 15 did the same thing. I started by taking the quick connect off the motor and off the fuel line then primed the bulb with the vent screw open and gas shot out of the hose. OK fuel to quick connect NOT past it. Replaced quick connect took it to the lake and it worked fine. You have a air leak or something bad in the line. just do like ahab said and you should be OK. :wink:

i forgot to mention, the fuel tank and fuel line is brand new, all the fuel lines in the motor are new, carb and fuel pump rebuilt nothing leaking or wet looking. i think i flooded it yesterday and fouled the plugs, i ran in a drum today first pull start like it was nothing, and had it running wide open and through all the rpm ranges in gear with no issues, if its running fine in a barrel, it should run fine on the water then right? thanks for all the input

I had brand new tank and hoses in mine as well - drove me crazy until I just fixed them and them no more problems

Hope you get it

thanks for all the help, im gonna give her a run this weekend, she runs great in the barrel with no issue so well see how she goes

I had a 48hp Johnson special that gave me fits when it came to starting and running in gear.

I found two problems. One was the floats were way off on adjustments and a kink in the rubber fuel line that was out of sight behind the starter.

Good luck.

Back pressure is one of the basic guiding factors when tuning the air/fuel ratio on a two-stroke outboard. When properly tuned on a hose the engine will be way off when the engine is actually on the back of the boat, in the water. You need to tune the engine with the static waterline at the normal position on the back of the boat in the water. The fact that the engine took a long time to start to idle properly and still would not accelerate indicates a lean condition. Richen the idle mixture and see if this helps. If not you may need to go back through the carb and check and clean the small passages inside it. The time you had it running in the barrel indicates nothing as far as troubleshooting goes. The water becomes so aerated in a barrel that it would be easy to accelerate to WOT.

pappy, i think your on the right track, my air fuel ratio was turned out 1/2 turn from full seat when its supposed to be out 1 1/2 turns and then fine tuned from there, i did all that the other night, and since then its running very nice, its gonna hit the lake this weekend. last time i took it there i couldnt get much more than idle out of it in gear, in the barrel it runs fine under load all the way up to wot back to idle and repeated through the rpm's i think its gonna be good this time around.... i hope! thanks again for all the help everyone

well i took the boat out today, it ran much better then the previous attempt but over all the engine is in bad shape, runs at about 10 mph wide open got it home checked the compression, finally got a compression tester, and both cylinders are reading about 60 psi, i figure its just stuck rings since the motor sat for 3 years before i got it, well see how it goes when i decarb and sea foam it and hope its just the rings and dont need to pull the head

Try squirting some oil into the cylinders before the next compression test if you haven't tried already. If the numbers get better, it may be a sign of bad rings.

Good luck.

60 psi is alittle low for that motor. First, lay the motor down with the cylinders facing up and pour some ATF/ACETONE mixture ( the trans fluid has exc cleaning-releasing properties and the acetone thins it out to penetrate easier) or pb blaster into each cyl and let it soak.
Try your compression gauge again after setting for some time to see if the rings free -up.
Or it could be a blown head gasket. It might have blown between the cyl`s so each stroke of compression is going into the other cyl.

You will not get your comprression back with any type of Seafoam or any other type of Witches Brew. Those numbers are way off the mark and you will not gain back almost 60psi with a decarbon agent. The 9.9 - 15hp engines I take in are normally in the 120psi+ range. Try a head gasket first since both cylinders are low. If the gasket is not blown inspect the clyinder liners, particularly on the exhaust side. You will be looking for scuff marks that you can catch a fingernail on. BTW - when you do want to decarbon an engine OMC/BRP makes a product called "Engine Tuner" that was developed specifically for that purpose, it does nothing else. Buy some and use it, it works better by leaps and bounds over any other product I have seen to date.

i decarbed the motor got a ton of carbon out, as pappy said, it didnt do anything for compression what so ever, when i said 60psi i was off, its reading 50psi both cylinders, so either way looks like the head needs to come off, i put oil in the cylinders, alot, and checked and the numbers didnt even budge what so ever. how often do head gaskets fail? its just too consistent in both cylinders to make me believe the cylinders or rings are hammered

Head gaskets fail primarily due to an overheat somewhere along the life of the engine. In your case that was probably the reason the engne was no longer used and you ended up with it.

Here is my headgasket replacement....

I knew/found I had a bad headgasket, when the engine was hard to start, would not idle smoothly, I pulled the top plug...it looked good...

I pulled the bottom plug...and the cavity between the electrode and threads was full of clear, clean water!

Now engine idles, and runs great.

https://www.tinboats.net/forum/viewtopic.php?f=4&t=21236

alright got some awesome news, i bought the motor after sitting for 4 years and not ran, when i picked it up i made sure it turned freely by hand and threw a compression gauge on it, it was a crappy one that was leaking more pressure then going in so we had to pull very fast, we got both cylinders up to 100 with the leaky gauge, so i know it had a minimum of 100 psi per cylinder like more due to not being able to compensate enough cranking to the leaking of the gauge, it sat at my house for 6 months until i got a new lower unit for it and rebuilt the carb and fuel pump, i let her soak in oil the night before it fired it, when i fired it it started first pull with a little spray of mixed 50:1 and it ran no problem without stalling or sputtering. tonight i got smart and took my compression gauge quick connect and brought my top piston up to tdc and hooked it up to the gauge hose and hooked my compressor hose to it with 60 psi held the flywheel with a homemade tool and had the spark plug out of the bottom cylinder, filled the cylinder with pressure and sure enough it i had whistling sound coming from the open bottom cylinder with air pressure coming out of it, the head gasket failed between the 2 cylinders, i pulled the head, it square and no warpage along with the block, cylinder walls are nice with no scoring or wear you can still see the cross hatches from the factory hone and looks great, i feel so much better that its just an 8 dollar head gasket, should have it back together by next weekend! i think from it sitting for so long the gasket got dry and brittle and after running the motor it failed due to this

Sounds like you lucked out. I hope it turns out well.

thank you, i hope all turns out well as well, ive got some money invested into it and was sick to my stomach to see why it had no power in the water