1990 Johnson 35HP 2 stroke bottom cylinder won't function

[Jay Ainslie]

Need help, i'm out of ideas...
I have a 1990 Johnson 35hp 2 stroke that is working only on the top cylinder. Both cylinders have excellent spark at the spark plugs. Compression is about 85 on both cylinders. Motor starts right up and when I pull the plug wire off the bottom cylinder, there is no change. I did a spark test with motor running on the bottom and spark is bright and at almost 1/2". I am now suspecting the fuel pump because I took off carburetor and removed and checked the reed valves. They were seating good... Any help would be greatly appreciated... Thanks Jay

 

[matthew daley]

Re: 1990 Johnson 35HP 2 stroke bottom cylinder won't function

hi if its twin carb try smuthering bottom carb by restricting bottom carm see if cylinder picks up sounds like dirty carb to me this will draw all the crap out of jets what colour is plugs are they the same have you switched plugs around to see if plug breaking down under compression

 

[Jay Ainslie]

Re: 1990 Johnson 35HP 2 stroke bottom cylinder won't function

HI, it's a single carb. Plugs are the same and I have switched plugs with same results. The bottom plug is wet with gasoline because it isn't firing, but then the top plug is kind of wet also (not dry) even though it is the only one firing..
Weird..

 

[Jay Ainslie]

Re: 1990 Johnson 35HP 2 stroke bottom cylinder won't function

actually I was thinking that the problem may be in the fuel pump... maybe diaphragm leaking fuel into the cylinder. Would an 85 compression be able to cause this; I believe compression should be around 110 right?

 

[Bosunsmate]

Re: 1990 Johnson 35HP 2 stroke bottom cylinder won't function

Check its fuel on the plugs and not water from a gasket leak

 

[Jay Ainslie]

Re: 1990 Johnson 35HP 2 stroke bottom cylinder won't function

hmmmm I will do that... even though the top cylinder is firing good... I will check the bottom

 

[Daviet]

Re: 1990 Johnson 35HP 2 stroke bottom cylinder won't function

If the fuel pump is attached to the lower cylinder it is possiable for a defective pump to flood the cylinder and cause it to miss. You need to either rebuild or replace the pump.

 

[boobie]

Re: 1990 Johnson 35HP 2 stroke bottom cylinder won't function

Which cyl is the fuel pump attached to ??

 

[Anchor Marine Repair LLC]

Re: 1990 Johnson 35HP 2 stroke bottom cylinder won't function

Your motor doesn't need a fuel pump to run. It idles off the fuel vapors that come out of your carburetor. A healthy motor will run 1-2 minutes with just the fuel in the motor side fuel lines. You can run any outboard without the lift pump in the equation, just install the fuel tank (without any check valves) several feet higher than the motor. It will gravity feed and run all day long. Since that's not practical there's fuel pumps.

If your compression is only 85 lbs each, that's the problem. The 2 cyl block that goes on the 25, 30 and 35 always run 120+ each on a healthy motor. Those are known for bad head gaskets, and you might have a washed out #2 cylinder.

A new head gasket won't be a fix, if the gasket is bad. There will be piston skirt damage at a minimum with only 85lbs compression. I've had successful repairs when the head gasket showed to be bad via a Leakdown test. But those had 105-110. Cheapest and easiest diagnosis would be pull your cylinder head and inspect. Any scuffs or scores on the cylinder wall will be proof this motor needs to be rebuilt.