Engine RPM

[fintastic]

I have twin 200 Johnson Ocean Pro's. I recently experienced a drop in the port motor of 800-100 rpm. I compression checked all cylinders are good. Changed all plugs, and used engine tuner. The port motor now runs within 400 rpm of the startboard but obviously still off. The motors sound great and pick up great but I'm not sure whats happening on the high end? I do not want to starve a cylinder. Could this be a carb problem? or is it possible the Power pack? Any ideas of where to go from here.

 

[Dhadley]

Re: Engine RPM

That rpm difference is about what we see if one cylinder isnt firing at wot. Assuming everything is the same as it was when they both turned the same rpm (props, carbs, ignition, water pumps etc) I'd use a timing light to verify each cylinder is at least getting spark. <br /><br />If you even suspect the carbs, rebuild them. That includes soaking them clean.

 

[fintastic]

Re: Engine RPM

Being that it has improved is a good thing? I'll do spark test. Coils resistance tests. So do you think I'm out of the woods in regards to cylinder/ring problem? <br /><br />Thank you!

 

[Dhadley]

Re: Engine RPM

Well, the compression test indicated all is well. <br />Which was a good place to start. Especially if the motors are being lugged (they need to be set up at 5800 with an average load). <br /><br />Since the Engine Tuner helped, it might not hurt to do it again. Did you change plugs before or after the Tuner?

 

[fintastic]

Re: Engine RPM

Before the tuner. I've heard conflicting stories on the tuner as weather you should change the plugs after using? SOem say yes others no? As for lugging, my book calls for 5000-6000 RPM @WOT.I now get approx 5200RPM @ WOT.I carry four-five persons gear tackle and 210 gallons of fuel along with weight of hardtop/tower & rigging on Mako 261B in primary bluewater and sometimes a very strong inlet current.Should I look for another set of props?

 

[Dhadley]

Re: Engine RPM

We generally would like to do the Tuner with old plugs and then change them afterwards. It might not hurt to try a new set. If they act the same you know you have a good spare set.<br /><br />5200 is pretty hard on the motor. At 5200 your combustion temps will be higher than we'd like to see them. That promotes coking which is that stcky black goo that causes the rings to stick.<br /><br />I wouldnt change to a lower pitch to gain rpm. You'll generally lose efficiency. We go to a lower pitch only as a last resort. You might play with the set up some. Try raising the motors a bit. That will reduce drag and increase efficiency. That will let the r's come up. It all depends on the props you have now.

 

[fintastic]

Re: Engine RPM

Yes I've gotten some of the black goo in the past during the winter mostly but have kept tuner going through it every 20-30 hours and fresh plugs. You think I should raise the motor height by moving to a different slot on the transom bracket.

 

[v12mac]

Re: Engine RPM

I am running the same hull and motors without the bracket, what pitch are your props? What kind of speed are you seeing on the gps?<br />Mac