74 evinrude wont start

[aggiechicken]

have a 74 evinrude 135hp. getting spark and fuel, but engine just turns over. just bought the boat, last owner said it ran last fall. has new plugs, coils. any ideas? thanks

 

[aggiechicken]

Re: 74 evinrude wont start

Also, the sparkplugs are NGK B7HS10 are these the right ones??

 

[emdsapmgr]

Re: 74 evinrude wont start

The older OMC engines always seem to run better with Champion plugs. You should invest in a set of 4 UL77V plugs. You need to know if you have a fuel or spark issue. When cranking, put an inductive timing light lead on each of the 4 plugwires. The flashes in the gun will show the condition/quality of the spark on each wire. Also, after cranking for a few seconds, pull a plug or two. If you are getting fuel, they should be wet. If they are dry, look for a fuel delivery problem.

 

[crb478]

Re: 74 evinrude wont start

Verify compression and as mentioned above switch plugs. It won't matter if you have spark and fuel without adequate compression

 

[Big flop]

Re: 74 evinrude wont start

The carbs may be varnished from sitting?
Can you here the choke working?

 

[aggiechicken]

Re: 74 evinrude wont start

ok, changed the plugs, getting spark, carbs are clean, getting fuel, and motor just turns over. going to check compression next. any idea how much I should have?

 

[emdsapmgr]

Re: 74 evinrude wont start

That was a very high compression engine. Compression would probably be 130+ on all 4 holes. It's important that the compression be within 10% between all 4 holes. It is not unusual for the cyls on one head to vary 5 lbs from the cyls on the other head.

 

[aggiechicken]

Re: 74 evinrude wont start

just got done checking the compression, 120lbs on both port cylinders, 105 lbs on both the starboard cylinders. Got it to actually run for about 4 seconds, then nothing after that.

 

[emdsapmgr]

Re: 74 evinrude wont start

When the engine quit running after those 4 seconds were the plugs wet or dry? You have a borderline compression problem. The starboard head compression is on the low side. I'd probably pull the head for a visual inspection. Check the head gasket, then check to make sure the top piston rings are intact. Also check for any aluminum transfer from the pistons onto the cast iron cylinder walls.