70 HP OMC WOT- only getting 5000

[rbc]

Motor is 70 hp 1985 Evinrude that seems to run good on 17 ' Boston Whaler with 13 X 17 prop. But cannot get over 5000 on Tach.<br /> Removed VRO today and just for kicks pulled cover over carbs. and checked WOT. The valves inside carbs only seem to open about 1/2 way. Could this be my problem? Can I just adjust the black roller that controls all 3 carbs so that at WOT valves are fully open? Any timing considerations? I am really tempted to try it but wanted to check with you guys first.<br /><br />thanks<br />RBC

 

[JB]

Re: 70 HP OMC WOT- only getting 5000

Get a manual, RBC, and do the complete linkage and synchronization adjustment procedure.<br /><br />Good luck.

 

[OBJ]

Re: 70 HP OMC WOT- only getting 5000

Intersesting rbc....5grand with throttle plates half way open....if you don't look darn near square into the carb bore, they will not appear all the way open. Before going out again, take the carb cover off and shift into forward (don't forget to spin the prop) and go to full open throttle. Now take a look down the carb throats and see what ya' see. The plates should be flat at WOT.<br /><br />Also, look on the port side of the carbs. The throttle plate shaft will be sticking out. The shaft has a pin through it. This pin should be vertical on all three carbs.<br /><br />Let us know what ya' find before we start messing about with the roller and stuff.<br /><br />EDIT: I think your operating range is between 5 and 5500rpm. Hopefully one of the other wrenches will keep me straight on this.

 

[rbc]

Re: 70 HP OMC WOT- only getting 5000

OBJ, the plates inside carbs are not flat at WOT and the pin is not vertical.<br /> But I did just notice what looks like a throttle stop screw just above the idle adjust screw. If I adjusted that out it should let plates go flat.<br /><br />RBC

 

[OBJ]

Re: 70 HP OMC WOT- only getting 5000

Yeah RBC...adjust it until the plates go flat at WOT. Don't let them roll over. Not sure if the screw is adjusted in or out. Adjust it which ever way works.....

 

[ob]

Re: 70 HP OMC WOT- only getting 5000

That 70 should rap 6000 wot with a light load.I'd be real surprised to see an 85 70 hp spin that 13 X17 prop to 6000 pushing a 17 Whaler.Anything under 5500 at wot is good reason to decrease prop pitch .<br /><br />After you get your stop screw set , insure that the carb link roller in on center with the scribe line on the throttle cam and just touching when the controls are in neutral.OBJ brings up a good point in not overshooting full open on the flaps ,or you'll decrease performance.It doesn't take much.Good luck.

 

[rbc]

Re: 70 HP OMC WOT- only getting 5000

Thanks Gents.<br /> I hope to do the adjust tommorow and toss her in the water if all the other little projects get completed.<br />I will let you know results.<br /><br />RBC

 

[JB]

Re: 70 HP OMC WOT- only getting 5000

Having run a JohnnyRude 70 on a BW 17, I must respectfully disagree with OB.<br /><br />6Krpm with a light load, 5500 with medium load running a 17" prop.<br /><br />The BW 16/17 are a lot lighter than you might expect. 850 to 950lb, dry.

 

[ob]

Re: 70 HP OMC WOT- only getting 5000

And you may be right JB..Engine optimally mounted and kept tuned.I've run nothing but Whalers myself .All with 60 and 70 horse J/Rs on 15 ft class . Did you use a double cupped stainless and get those R's JB or a single cupped aluminum?Just curious.

 

[JB]

Re: 70 HP OMC WOT- only getting 5000

Used the AL prop supplied by the dealer, OB.<br /><br />According to the Ft. Lauderdale MP, she was at 38mph at WOT and 6Krpm. Very light load that day.

 

[rbc]

Re: 70 HP OMC WOT- only getting 5000

JB, what engine mount hole do you suggest?<br /> Mine is mounted at top hole.<br /> The odd thing is that the top bolts obviously go thru top hole and a nut and washer is on engine side,but the bottom bolts are not coming out thru "blind hole'. Are these bolts going into engine casting??<br /><br />RBC

 

[ob]

Re: 70 HP OMC WOT- only getting 5000

Thanks for the reply JB.Always wanted a Montauk but can't fit it in the garage.<br /><br />rbc,If I'm not mistaken the engine brackets bottom holes are a long slot and should have the bolts long enough to extend thru and nutted.The top bracket holes are individual.If your engine is mounted with the top bolts thru the highest top hole of the bracket ,you've got upward adjustment to raise engine.A rough setting is to have the engine placed where the anti-ventilation plate of the lower unit is even with the bottom of the hull at transom when engine is trimmed level with hull.Only a water test will confirm final optimal placement.

 

[rbc]

Re: 70 HP OMC WOT- only getting 5000

Thanks Gents !<br />I adjusted throttle stop so that WOT has carb butterflys full open. Today I was able to run at 5600 rpm. Much better.<br /> This is a 1985 should I be worried about running for awhile at WOT as long as I can pay for the gas?<br /> Anybody know what would be most economical cruise RPM's?<br /> Still running 17 pitch prop, maybe 15 will get me to 6K. Or maybe I better quit while I am still ahead.HA<br /><br />RBC

 

[Solittle]

Re: 70 HP OMC WOT- only getting 5000

You should be able to run at WOT until you run out of fuel without hurting your motor. I would think that the most economical rpm would be around 5k. I think the rule of thumb used to be max rpm at WOT less 10%. Many motors have a sweet spot that you can hear (but can't be described).