omc 3.0 rpm's

[liesight]

I have a 1986 omc 3.0l, the tech manual says may rpm's are 4500-5000 rpms. When at w.o.t. on a smooth lake (lake mead), with no wind, my boat hits about 2200 rpm's about 33-35 mph . Now here is my question, my tach even though very old seems to work ok, I timed the engine with the 600rpm mark and it seems right on. I have checked the throttle linkage and it is engaging 100% at full throttle, (I think), so is the tech manual wrong? Is 2200 rpms the most I can get from my engine? Does it have some type of rev limiter on it. It has the rochester 2bbl carb. It runs great, but the difference in rpm's has me wondering, is my tach gauge wrong? Is something else wrong?<br />If anyone has experience with this engine please help.

 

[DJ]

Re: omc 3.0 rpm's

liesight,<br /><br />You do not say what type of boat you have, but your numbers seem awry.<br /><br />Your engine should turn 4400-4600.<br /><br />Look on the back of your tach. and see which "pole" it is set on.

 

[Walt T]

Re: omc 3.0 rpm's

I agree, tach is most likely inaccurate. This could also be related to your other problem of the boat shutting down. Disconnect the tach from the coil, see if that problem goes away.

 

[dhammann]

Re: omc 3.0 rpm's

Either your tach or speedo is wrong. It is theoreticly impossible to run 35mph at 2200rpm with a 3.0 and matching outdrive. 35 at wot is about tops for a 18-20 foot boat.

 

[Boatist]

Re: omc 3.0 rpm's

Liesight<br />Tell us about your BOAT, (length, wieght,type hull).<br />My guess is your tach is set for a 8 cylinder engine. If it is the stanadard OMC tach it will have a lever on the back to set it for a 4,6,8 cylinder engine.<br />I also think you will get more power and RPMs if you adjust your valves to proper setting.<br /><br />My boat spec for comparison: 21 foot, Deep V, Aluminum, 92 inch beam, wieght 2800 lb Dry. WOT I turn 4500 RPMs at 38 MPH with a 13 3/8 by 17 pitch 3 blade Stainless steel prop. Engine OMC 140 HP 3.0L 181 cubic inch 4 cylinder.<br />Engine spec: WOT range 4200-4600, dwell angle 31-34, Points gap .019, Timing 4 degrees before top dead center, Fuel pump at idle 3.5 to 6 PSI and one pint in less than 45 seconds, Valve lash- one turn down from zero lash point, idle RPMs 500-600.<br />Hope that helps, good luck.

 

[geriksen]

Re: omc 3.0 rpm's

These guys are all right, 2200 rpm and 30 mph don't add up. If the switch on the back of the tach is set correctly, replace the tach.