35 hp Johnson Lean Sneeze / Pop causes

mato0010 · May 3, 2010

I have a 1976 35 hp Johnson Seahorse that Im having issues with. Ive gone through several checks and replaced enough that I just cant figure it out. The motor starts but when I have it running at idle, it sneezes and pops which all indication points to a lean air/fuel mixture. Here is what I have done so far:

Fresh Fuel.
New Water Pump.
New Thermostat.
New Spark Plugs. (Checked and have good spark on both)
New Head Gasket.
Cleaned Fuel Filter.
New Fuel Pump Gasket.
Carburetor Cleaning.
Did compression test and have 122 psi on lower and 119 psi on upper.

When I replaced the head gasket, I noticed that the upper spark plug and head were oily and the lower was black. Everytime I remove them and clean then test again, they come back the same with the top being oily and the bottom being dry but back coated. I dont know the reasoning for this.

Here is a link to a video that shows the motor running.

http://www.youtube.com/watch?v=-i3BAs3b76Q

What else can I check or fix? What else could be causing this? Thanks much.

bktheking · May 3, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

Remove the intake and inspect the reeds, you may have one stuck open or not seated properly.

mato0010 · May 3, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

I did a visual inspection of the reeds when I had the carb off and they looked ok. I will take the carb off again and pull the leaf plate to see for sure.

While I have everything off is there anything else I should check before I put it all back together again? Should I pull fuel hoses and blow them out? Also, when I did the carb cleaning I couldnt get the high idle screw out. I cleaned as best as possible but could that be the cause? I also didnt remove any of the core plugs which Im also going to try now.

bktheking · May 3, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

You may also have a bad upper crank seal, inspect for oil under the flywheel around the crank snout. Core plugs are essential to a proper cleaning , that could be the entire issue, do that first before the rest and see how it runs, it's a lean sneeze , you should be able to richen the mixture to eliminate it at idle.

mato0010 · May 3, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

"......you should be able to richen the mixture to eliminate it at idle. "

Yes, when I close the choke about half way it runs smooth. Would this also cause my upper spark plug to consistantly get oily?

blimp · May 3, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

I had the same issue and a link-n-sync cured it. You'll need a factory manual, but it is very easy to do.

Cofe · May 3, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

Yes it does sound like a lean sneeze. Cleaning the carb correctly should take care of the problem.

If the problem persists, check the exhaust gaskets for water internal leakage. Sometimes, a bad gasket will allow cooling water to get into one of the cylinders and make it sound like a lean sneeze. Here is a pic of the gaskets location.

F_R · May 3, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

How far open do you have the idle mixture screw? Don't be afraid to open it. 2 1/2 to 3 turns on some of them. Also, I have to ask--the 1976 was notorious for overheating. Has yours ever ran hot? If it has, you may have piston skirt scoring.

A tad less drastic, you could have a bad lower crankshaft seal, letting air into the lower cylinder, making it leaner than the top one. That would account for the top one to be richer and fouled.

mato0010 · May 3, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

Thanks Cofe, I will definitely check and replace the exhaust gasket too.

F_R, Ive backed out the low speed idle screw and no differences. Ive tried from 1 turn out to several and no differences at all.

Yes, last year it did overheat.....water impeller fin broke. These engines didnt have warnings on them. I replaced water pump to fix problem. If I had piston skirt scoring, wouldnt my compression tests show a significant drop. No other way to inspect those other than disassembling the power head which is my last resort (crossing fingers).

I have a service manual so yes I will try my throttle cam and throttle control adjustments but that again doesnt give reason to the oily plug....or would it?

Cofe · May 3, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

When you remove the exhaust cover and water port plate to replace the gaskets, you will be able to see some of the piston skirts threw the exhaust ports.

mato0010 · May 5, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

F_R,
You mentioned a possible crankshaft seal. I pulled the reed valve off and all looks good except for having to replace gaskets. Looking inside the crankcase, there were small droplets of oil residue in a couple places behind the reed valves. Should I be concerned....possible reason for oily plug on my top cylinder because that would be the crank for the top plug.

Is there anything I can look for or check while I have a look inside the crankcase? Not much I can do in there but at least I can look.

Also, I was told on 2 strokes that a good compression test would rule out crankcase and piston problems, different from 4 stroke. I had good compression 119 psi and 122 psi so should that indicate Im ok back from there?

mato0010 · May 7, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

OK, Heres a status update. Did the carb cleaning (thoroughly), reed valve check, replace all gaskets, fuel pump checks and fuel lines. Still had same problem.

Then as recommended by Cofe I pulled the exhaust housing and think I found my problem. Water residue showed that the gaskets were leaking plus the inner exhaust cover was completely warped. I have those parts on order and should know for sure next week.

Another possible cause could be this. On the left side of the exhaust there is a thin chamber for water circulation. In the middle I noticed a peice of debris which after several minutes of trying to get out, finally discovered that it was a peice of rubber hose which was stuck in there and clogging a hole about the size of a wood tick. Im sure that hole was not allowing much water to pass through and could have added to the whole problem.

Here are some pics. I will follow up with more next week after I replace the exhaust parts and fire it up again. Going to do a good decarb once thats done and hopefully should be good.

Anyone know more about that hole in the water chamber? What way does it circulate? What problems would that cause being clogged?

Here are some photos.

F_R · May 7, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

That hose is called a water deflector. It causes the water to circulate around the cylinders in the proper direction.

Looking at your pictures, I believe I am seeing scoring on the top piston and black blow-by on the bottom one. A closer look may be in order.

Reguarding your previous question, good compression only indicates the rings are doing their job. Unlike a 4-stroke, two strokes have to have crankcase compression. The piston skirts seal off the exhaust area from the crankcase. Crankcase leaks are also related in that they admit air to the crankcase.

mato0010 · May 7, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

Im not sure what you are referring to as the deflector. There is just a hole there and no "hose". Im referring to the area along the left side of the exhaust. Its about 1" wide. There is a small hole in the middle back of that section.

As for the piston skirt, I checked those and there didnt seem to be any scoring. I felt them as best as I could with my finger and no abrasions. There was oil residue on them from the water splashing back from the bad gasket which makes it look like marks on the piston skirt but they really did look in good condition. There is a bunch of carbon build up which once the water hit would turn black and got on the pistons too. They felt smooth so I dont think that is a problem.

Cofe · May 7, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

I agree with FR, a close up pic of those piston skirts is needed.

From what I can tell, looks like your exhaust housing was subject to piston blow by. The added heat and pressure would deform the inner exhaust cover allowing cooling water to get into the exhaust ports.
The top piston looks to be scored. As FR noted, a crank case needs to be sealed, some more pictures would help.

Cofe · May 7, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

Water deflectors are usually pieces of 3/8" outside diameter rubber hose.
Some motors have them in the exhaust water cooling ports. Here is a pic of where the deflectors go in the block.

mato0010 · May 7, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

Ok now I know what your referring to as the water deflectors and when I replaced the head gasket those were good.

I referring to the section on the left side while facing the exhaust. There is a big hole in the bottom and a small hole in the back middle. The piece of hose was a triangular peice that looks like it broke off of something. Very small and got clogged in the small hole.

Here are a couple more pics of the piston skirt but like I mentioned they felt good. They look like there is scoring because of the black water + carbon splashed on it from the bad exhaust gaskets. I felt them and no abrasions.

Cofe · May 7, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

Sounds like the rubber chunk you found may be a part of an old impeller, or grommet. It could have caused the over heat warpage of the inner exhaust cover.

If you like the way your piston skirts look, a good decarb would likely help once you get it back together. Thanks for keeping us posted on how things are going.

F_R · May 7, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

I apologize for my suggestion about the deflector. I was thinking you had the cylinder head off, which obviously you don't. Agreed. you probably found a piece of an old disintegrated impeller.

You are there and I am here, and you can see the pistons better than I can. I hope I am wrong in my judgement there too.

Carry on---

mato0010 · May 11, 2010

Re: 35 hp Johnson Lean Sneeze / Pop causes

Well Im back to square 1.

Last night I replaced the Exhaust gaskets and inner cover which I thought was my sure problem.....come to find out was not the problem and now Im back to banging my head against the wall. Im not a mechanic and after this I hope to never be. Can anyone please help me diagnose this and recommend my next course of action.

I keep going back to the spark plugs because its evident that whatever is causing this is leaving my upper spark plug oily and my lower spark plug black (but dry). Everytime. I decarbed yesterday thinking that might help but still nothing. My only thoughts lead back to the pistons and rings but my compression tests tell me different. What would cause the oily plug? I was told to check my timing. What does that check for? Also, I was told it could be a crankcase seal and to spray carb cleaner around where the crankcase and piston case are bolted together, if it sucks that in and smoothes out then theres the problem. I did that and no differences there. I just dont know anymore at this point and Im looking for some direction which could also give me a little motivation. Its depressing to go through all the work and not have any results.

35 hp Johnson Lean Sneeze / Pop causes

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