82 Johnson - No Combustion

[sah440]

I have an 82 Johnson 25hp w/ electric start. I am getting spark in both cylinders but no combustion. I sprayed fuel down the throat of the carb and still nothing happened. The flywheel spins but there is not combustion. Electric problem? or fuel delivery problem??

 

[Joe Reeves]

Re: 82 Johnson - No Combustion

Has this engine run properly in the past for you? Has it been sitting for some time?

With the spark plugs removed, the spark should jump a 7/16" gap with a strong blue lightning like flame.... a real SNAP! Does it?

What are the compression readings of all cylinders?

Spraying fuel into the carburetor throat should have cancelled out any fuel delivery problem as you would be delivering the fuel fairly well direct. Did you also try spraying some fuel directly into the cylinders, then installing the spark plugs?

If you have fuel, spark, and compression, the engine has to run.

 

[sah440]

Re: 82 Johnson - No Combustion

Has this engine run properly in the past for you? Has it been sitting for some time?

With the spark plugs removed, the spark should jump a 7/16" gap with a strong blue lightning like flame.... a real SNAP! Does it?

What are the compression readings of all cylinders?

I have never ran this motor. I got it really cheap and could part it out for double what I paid. Therefore I do not know what the compression reading are.

After reading your comment I believe the spark is too weak. I bought an in-line spark checker. It doesn't have an output device, only a light that indicated that there is some type of spark present. And thats what I see - it lights up. But I did not see a blue arc when I removed the plug. Not sure if I heard a snap either because the motor was attempting to start.

To answer any future questions: I have a brand new battery. It is fully charged. I load tested it in addition. The ground connections are clean as well as all other junctions.

Some of the wiring in the motor cable assembly is beginning to corrode. Could this create enough resistance to supress my spark???

 

[sah440]

Re: 82 Johnson - No Combustion

could it possibly be a bad gasket??

 

[highcountry]

Re: 82 Johnson - No Combustion

If you put your finger tight over the plug hole and turn it over does it blow air hard? Are the plugs wet?

 

[boobie]

Re: 82 Johnson - No Combustion

If you're going to keep it, go back to step one and check the compression with a gauge.

 

[Joe Reeves]

Re: 82 Johnson - No Combustion

Exhaust fumes...... Engine on a boat and in the water, it's a different story as the exhaust fumes get pretty well spread around and away, BUT in a barrel or test tank those fumes are just sitting and trapped under the engine.... only one place to go when you put the hood on.

 

[dew2]

Re: 82 Johnson - No Combustion

heres one of the many testers where you can see the spark jump,it can be set to different jump distances
http://www.toolfetch.com/Category/Automotive/Spark_Testers/LIS50850.htm

 

[sah440]

Re: 82 Johnson - No Combustion

Exhaust fumes...... Engine on a boat and in the water, it's a different story as the exhaust fumes get pretty well spread around and away, BUT in a barrel or test tank those fumes are just sitting and trapped under the engine.... only one place to go when you put the hood on.

????

 

[kbait]

Re: 82 Johnson - No Combustion

Electric start/choke cables shouldn't mean anything if you've got spark and it spins over. It is a self-contained ignition, and doesn't require 12v battery for anything. And if you're getting spark, the kill switch wires aren't grounding together. Check compression, and put a bit of premix into the plug holes (after you've pulled it over a bunch of times w/plugs out to make sure it's not flooded) and give it a try. It should fire up for a few seconds. If it does, you have a fuel delivery issue. If you then can't get it to fire by squirting some premix in the carb, perhaps you have a reed plate/valve issue or bad crank seal(s)?? First things first.. check compression and check for proper spark, then premix in plug holes. Good luck

 

[Joe Reeves]

Re: 82 Johnson - No Combustion

The reply about exhaust fumes somehow got cross posted from another area, sorry.

 

[dew2]

Re: 82 Johnson - No Combustion

????

Exhaust fumes in through the carb are very low oxygen=no combustion.