Rebuilt '90 70HP Evinrude - de-carb?

[bshellrude]

Just a quick question for all of you.<br />I've recently reached my 20 hour break-in following a complete powerhead rebuild on the above engine.<br /><br />My compression when cold is 100, 95, 98. This is using a push-in gauge, not a screw in one. After speaking with a local marine tech, he said that's typically lower than he would like to see on a rebuild.<br /><br />My question is this, due to running double oil for the first 10 hours, is it possible that carbon has built up enough to skew compression? That aside, should I perform a de-carb now that the engine is tuned and broken in?<br /><br />Thanks in advance.<br />Ben

 

[JB]

Re: Rebuilt '90 70HP Evinrude - de-carb?

I think your readings are more guage dependent than actual compression dependent, Ben. Your wrench almost certainly uses a screw-in guage and very consistent technique. Your numbers are fine.<br /><br />It is very unlikely that 20 hours would build enough carbon to make a difference.<br /><br />Don't worry about the psi, worry about the spread. A 5psi spread is excellent for an engine that is still getting seated.<br /><br />Good luck.

 

[bshellrude]

Re: Rebuilt '90 70HP Evinrude - de-carb?

JB, thanks for the input. Much appreciated! <br /><br />So then, one other quick question... When should a de-carb be performed. I've seen a number of posts suggesting every 50-60hrs?<br /><br />Thnx<br />Ben

 

[JB]

Re: Rebuilt '90 70HP Evinrude - de-carb?

50-60 hours is okay.<br /><br />Depending on how and how much you use it I think annually (Spring) is okay, too.

 

[DJ]

Re: Rebuilt '90 70HP Evinrude - de-carb?

Agree with JB on the decarb interval.<br /><br />Make sure the engine is propped to run at least 5500 RPM with a light load.

 

[Dhadley]

Re: Rebuilt '90 70HP Evinrude - de-carb?

Absolutely!<br /><br />The 3 cylinder motors are very happy at 5800-5900 with an average load. Like DJ says -- set it up to at least 5500.