Low Compression? No Spark

[Salty Tricks]

1991 200hp Evinrude<br /><br />After weeks of putting together all the accessories I wanted to install on this boat I tried to fire it up. First I wanted to know how my compression was and was shocked to see low numbers. Are these normal for this motor. I am used to numbers higher than 100 psi<br /><br />70,66,70,70,75,73<br /><br />I also decided to check my spark and low and behold no spark on any plug!!!<br /><br />Last time out engine was hard starting, my mech put a new power pack on. Still wasn't starting easy so I pulled the boat(couldn't get on plane while riding to the ramp) Out of the water I change plugs and filter and it started right up on muffs. I put it to bed for the winter until now. I only bought this motor in September and at first it ran the boat quite good ..about 30 knots top end for a pretty heavy 23 footer. I was really satisfied with that. The motor appeared to be a well cared for engine when i bought it and,as I said my first few trips went very well.<br /><br />I'm a bit shell shocked and could use some advice

 

[Joe Reeves]

Re: Low Compression? No Spark

The engine should be checked for spark, and obviously for compression with the spark plugs removed. The reasoning for having the s/plugs out during the spark test is that you want the engine to turn over as fast as possible.<br /><br />The engine must turn over at least 300 rpms in order for the stator to deliver approximately 300 AC volts to the powerpack in order to energize it.<br /><br />Should you have a slow cranking engine, you would have either weak or non existent spark/ignition. A slow cranking engine could be due to a faulty batteryc, loose cables, tight but dirty/corroded cables, etc etc. If this is the case.... check everything.<br /><br />Compression on the OMC engines was dropped at some point in the 1980s to compensate for the poor quality gasoline we were faced with. Bottom line is that your engine should register about 90 psi compression.

 

[Salty Tricks]

Re: Low Compression? No Spark

Joe<br /><br />I charged both batteries and cleaned all battery connections before I took the compression test. The engine seemed to crank strong at good speed....enough to register the tach. I am wondering if when I was wiring some accessories I somehow disturbed the cut off circuit. However my manual (Clymer) is unclear how to eliminate this circuit for troubleshooting...it does not tell me color of wire to disconnect. It tells me to disconnect two single pin amphenol connectors. I found one...maybe? But I am not sure. Is there another way?<br /><br />Re: the low compression. I seem to recall I had my mech take a compression test before installing on my boat and he thought the numbers were low also (I don't remember the actual numbers)...HOWEVER, when we installed it, it ran very well and, as I said, I was quite pleased. <br />It is possible that my compression gauge is not totally accurate but I was shocked to see such low numbers.

 

[Joe Reeves]

Re: Low Compression? No Spark

Plugs out, key on, check spark. If no spark, disconnect main RED electrical plug at engine. Recheck spark by jumping the starter solenoid battery terminal to the small 3/8" nut terminal that energizes the solenoid/starter.<br /><br />If you now have spark, the usual cause is a failing ignition switch. To test switch, reconnect main RED electrical plug, then remove the black/yellow wire from the raised "M" terminal of the ignition switch. Recheck spark.<br /><br />If you still have spark, replace the ignition switch. Let us know what you find.

 

[Salty Tricks]

Re: Low Compression? No Spark

Thanks Joe <br /><br />will let you know tomorrow when I get to that.<br /><br />About the compression...should I be really worried about these numbers or the fact that this engine did seemed to run fine with what I believe were low numbers before?

 

[Joe Reeves]

Re: Low Compression? No Spark

Compression.... The difference between the lowest and highest is 9 psi. That's not good but not too bad either. What I see wrong is that none of the cylinders approach the 90 psi mark.<br /><br />With all of the spark plugs removed, try a different gauge to see if you obtain a higher reading.

 

[voodoo]

Re: Low Compression? No Spark

Unless the guage is in bad condition that motor is in trouble.<br /><br />Even then you ar 10+ % apart with the same guage.<br /><br />Maybe a peak inside?

 

[Salty Tricks]

Re: Low Compression? No Spark

Okay<br /><br />I separated the red connector and hooked up a remote starter switch. Hooked up plu leads to a homemade spark gap tester. Sure enough I got spark. Played with the cut-off switch. recrimped some connectors and I was getting spark from the ignition switch. I can't say the spark was strong and I failed to start the motor although she wants to. Sneezes and coughs but can't get it to start. BTW Primer bulb does not pump up hard.

 

[Solittle]

Re: Low Compression? No Spark

On the primer bulb - Check for air leaks in the fuel lines or you may have crud in one or more of the carbs.

 

[Joe Reeves]

Re: Low Compression? No Spark

The spark, with the spark plugs out, must be a strong blue lightning like flame.... a real SNAP!<br /><br />Anything less indicates a weak erratic spark, usually caused by a failing stator. Check the stator under the fywheel to see if there are any cracks and a oozing out of a sticky substance that would be dripping down on the timer base and block. If so, replace it.

 

[Salty Tricks]

Re: Low Compression? No Spark

Thanks Joe ( and others)<br />I guess that means pulling the flywheel!<br />I pulled the flywheel on my other engine (1985 Johnson 90hp) and I learned to use an impact wrench to get that nut off. I assume I'm looking at the same thing here.

 

[Joe Reeves]

Re: Low Compression? No Spark

I neglected to mention above.... the gap the spark must jump on that spark test would be 7/16".

 

[Salty Tricks]

Re: Low Compression? No Spark

Thanks Again Joe<br /><br />I actually did have my homemade gauge set at 7/16" gap. The results were inconsistent... some would fire and not fire...some would have nice snap and blue spark some were weak. I believe I back track on the entire Ign. system. Oddly when I had the remote switch hooked up control harness disconnected, no prime the motor actually started up albeit poor idle! When I hooked everything back up it wouldn't start although it did cough and sneeze.