25 HP Johnson Year 2000 J25RSSE Thermostat or Carburetor Backfires then stalls

[w2much]

This motor has some issues . New to me would not stay running. I did a basic carb cleaning. I did not soak as I normally do because I was hoping for a quick fix. I did however do a thorough job cleaning all of the orifices making sure they all carried a nice spray of carb cleaner through them then reassembled.installed and started it up. I have to have the idle adjustment screw out at least three or more turns for it to keep running. Occasionally it will still sneeze and quit. The test tank ( a large barrel ) has a large amount of gunk in it from unburnt fuel I guess. I have seen this on many outboards previously when running poorly. This thing smokes like crazy also.. For this issue I have ordered a carb rebuild kit. When it arrives I will soak the carb and do a proper rebuild.
The sneeze and stall seems odd in that if the carb is running super rich and creating all the gunk in the tank and excessive smoke why would it sneeze as if lean then stall?
I was wondering also if a stuck open thermostat would give me the same symptoms? The motor does not heat up higher than 130 degrees. It spits water out the telltale shortly after start up then out the exhaust relief a couple of minutes later.

 

[F_R]

Several issues there.
1. Gunk in the barrel is normal. So is smoking (in a barrel). Put that out of your mind. It was made to run on a boat on the lake, not go barrel cruising.

2. Some of those carbs do require the low speed needle to be turned out more than expected. Mine does.

3. Weather (air temperature) makes a difference. Back to the barrel cruising issue. If you were running it on a boat on the lake with the hood on, it would be breathing slightly warmer air. But trying to run it in a barrel with the hood on is futile.

4. Other things can cause lean sneezing. Not the least of which is a leaking crankshaft seal. Or as simple as a busted recirc hose.

5. Sure, a stuck thermostat can cause it to run cool. But the honest truth is that those motors do a poor job of regulating temperature. Too much water bypasses the thermostat through the pressure valve. Mine doesn't warm up worth a hoot.

6. Water discharge sounds normal as you describe.

 

[w2much]

" Barrel cruising" !!!!! I love that term. Kind of describes my hobby. When not on my boat I "barrel cruise " on my driveway. I joke with friends that I enjoy messing with out boards almost as much as I enjoy going out for a day on the water. Love the smell of two stroke in the morning.
I agree with you on the gunk in the barrel being normal. But I must add that a motor running poorly will spew a heck of a lot more of it than one properly tuned.
As for the smoke I am quite familiar on the amount to expect. Again this thing smokes more than my 2 stroke 150 EXEOM. My thought is it is running so rich that the excess smoke and gunk are a result of its problems.
I appreciate your input, just hope the lean sneeze stall is corrected by the carb rebuild .

 

[F_R]

With the new information we now have, it would seem that you are more knowledgeable than the novice monkeying around with a motor for the first time and shocked that it smokes and barfs oil. Sorry I misjudged you.

Nevertheless, the thoughts I shared are my best. I assume you are thinking it is running rich on one cylinder and sneezing on the other. That could be. That points back to the crankcase leak possibility(?) Hope you find the problem.

 

[oldboat1]

I also get comments like you describe (time spent tinkering in the driveway). Thing is, tinkering is fun too.

You could have a fuel pump issue (pump diaphragm), or ignition issue. Think I would do spark and compression tests if you haven't done that, and check out the diaphragm.

 

[w2much]

FR. I do truly love the term "Barrel Cruising" As far as being "novice monkeying around on the driveway" VS an experienced outboard tech you are probably closer on the novice thought not having wholly misjudged me . As far as an apology, you are a gentleman and trust me none is necessary.
I did enrich the idle a bit more thanks to your reply and have not had the sneeze yet. I have the idle screw out about 3 1/2 turns. I sprayed a bit of starter fluid up under the stator and around the crank case block union. Nothing happened so I assume that is a good thing, no air leaks there,again assumed. Motor is running a bit better since enriching the idle. I will still be soaking and rebuilding the carb when the kit comes . But boy ohh boy does that engine smoke and make a mess in the water.
I will also check the fuel pump . I have had bad fuel pumps in the past but usually they would flood out the engine and only run on the top cylinder. (on 2 cylinder motors). Good suggestion as the bottom plug is a lot blacker and wetter than the top. It is running on both cylinders as I have tested that. Perhaps there is a pinhole vs a total diaphram failure allowing it to run extra rich but not totally flood out the bottom cylinder.

 

[jakedaawg]

The pin hole would not explain the lean sneeze if in fact it has one. Good friend has exact same motor. Sneezes 3 times thenew is good for the day, never have been able to solve it.

Have you tried a can of brp engine tune then a good strong run to clean it.all out? Then.new.plugs.and see where you are at.

 

[w2much]

Been thinking on it also. Good thought. Thanks. Will barrel cruise it today. Carb kit should arrive saturday.

 

[w2much]

Been thinking on it also. Good thought. Thanks. Compression is even at about 100psi, bottom plug darker than top plug, both quite wet with fuel. Will barrel cruise it today. Want to cold start now after enriching idle mixture.

 

[w2much]

OK So the cruising today ended badly. When I received this engine I checked the compression and spark. Both cylinders were at 100 PSI. Both had hot blue spark which would jump about a half inch. With the motor running I removed the spark plugs one at a time to be certain each hole was igniting and therefore running on both cylinders. The engine ran better on the bottom plug than on the top plug. I assumed a carb and plug cleaning was in order. I performed both and the engine ran a lot better but still a sneeze and stall persisted. I followed FR and enriched the idle mixture. Motor seemed to run better. Today it started up easily but seemed to be running on one cylinder. I checked and sure enough. The top plug porceline is clean and white. The bottom plug is wet and firing. The motor will run on the bottom cylinder with intermittant firing on the top cylinder. There is constant spark going to the top cylinder it is just not igniting.
So I guess I have solved why the excessive smoke and excessive gunk ( unburned fuel and oil ) in the test tank. My thought is water intrusion into the cylinder thus all the smoke and gunk..
What are your thoughts?
Head gasket?
Exhaust cover gasket ?
I hate when this happens. Especially to salt water engines. Each bolt is a prayer to come out without breaking. And then whats inside may be an unwanted surprise. Kinda like eating Cracker Jacks and hoping for the better surprise inside. You may get a whistle or a wash off tattoo or you may end up with a pink ring you have to give to your little sister.

 

[racerone]

Checked the fuel pump ??------Does primer bulb go hard ?---Does spark jump a gap of 7/16" on both leads ?

 

[w2much]

The primer bulb goes hard, the spark jumps 7/16 on both leads.
I am not familiar with this fuel pumps operation. There is a pulse hose going to the bottom cylinder and the pump is attached to the upper cylinder on the crankcase. I am quite familiar with the smaller older pumps which attach at the crankcase to receive pulse through the hole in the back of the pump. On this pump does it receive receive a pulse through the pump body and the hole in the back or just through the pulse hose ? Usually when the pump is bad the fuel will flood out the bottom cylinder. At least that has been my experience. Would it flood the top cylinder but not the bottom one/?.

 

[w2much]

OK Tried again. I unhooked the fuel pump and plugged both pulse upper with a bolt and lower hose with a bolt pushed in.Hooked the fuel to carb and let it gravity feed. The primer bulb gets hard. I am fairly certain the carburetor is not the problem. Motor runs well on bottom cylinder. The top cylinder is firing with a hot blue spark which definitely jumps 7/16" it is just not igniting in the hole. Have tried different plugs with the same result. I can start the engine and run it with the top plug boot off or on and it will run on the bottom cylinder. When I try to run it with the bottom plug boot off it will sputter and stall . It will not run on the top cylinder. The compression is 100 psi per cylinder probably higher as my tester is harbor freight and always reads low.
Where to go from here ?
If the head gasket is bad would I read lower compression on the top than the bottom cylinder?
Appreciate the replies.

 

[racerone]

Check the reed valves.

 

[w2much]

Can this be done through the carb hole (for lack of proper term) ? Or does the manifold need to come off?

 

[w2much]

Thought I would follow up on this one. Carb rebuild, fuel pump rebuild, great spark, even compression. After all of this it runs well enough but I am not comfortable with it.So I let it sit and would start it when I had the chance. Each start attempt would be successful. I kept trying to convince myself that the smoke and gunk and sometime running on one cylinder was acceptable and that a good run would perhaps fix the issues. Today I tried to barrel cruise . She would not start. I pulled the plugs and they were soaked with fuel. So somehow it was flooding. Although I thought I had checked the primer to my satisfaction I rechecked it anyway. Sure enough as long as the engine was running fuel was or is passing through the primer. I unhooked the primer system and plugged the fuel line to it. In a few minutes after the smoke cleared I realized I had solved the problem. My primer pump assembly is /was bad. Way to much fuel entering the crankcase, same symptom as a bad fuel pump which I had replaced.
Now to either purchase a new primer pump assembly or attempt to rebuild the existing one. Looks to be just a matter of O rings. I am of course leaning toward the rebuild. Hopefully my harbor freight O ring kit will have the correct sizes needed.