What could be the problem?

[The Shoe]

Kk gang, thanks for the help with my earlier problem of motor not wanting to run under load (cleaned and rebuilt the carbs)<br /><br />Now, the new problem...this 70hp 1985 Evinrude has done this since I bought it last year....it is slow on acceleration! When I give it throttle,it raises the bow and will not "grab" and take off for probably 15-20 seconds (thats forever in a fishermans life). When it does catch...it takes off like the space shuttle.<br /><br /> I thought when I rebuilt the carbs, that may take care of that problem as well...nope! Motor is mounted on a 15 foot Dixie Bass Boat. I've tried playing with the trim..it just seems like it takes sometime for something to realize I want to go faster. Motor does not seem to pickup right away.

 

[R.Johnson]

Re: What could be the problem?

It sound's like you are over propped. Drop the pitch a couple of inch's.

 

[Solittle]

Re: What could be the problem?

What rpms are you getting at WOT? That will answer the prop question. When on a plane is the bow level, low or high?

 

[The Shoe]

Re: What could be the problem?

When on plane...bow is level. I'll check rpm at wot tomorrow and report back.

 

[ob]

Re: What could be the problem?

If propped correctly,expect rpm numbers from 5500-6000 with an average load.Anything under 5500 is overpropped or engine setup is too low.Also try to get some numbers off the prop you are currently running so someone can help ID it for dia and pitch.

 

[marinemech]

Re: What could be the problem?

there is an upgrade to carbs on that modle year<br />to see if you need upgrade (with boat in water moter running not tied to dock)shift moter into reverse and give it full throttle.<br />did moter stall?<br />if it stalled it requires up grade<br />remove core plugs from top of carbs and enlarge holes in off idle circut unfortunatly i can't remember size i think it .057 but not sure maybe someone else remembers? the fellow who told me about this is a retired tech rep from omc

 

[The Shoe]

Re: What could be the problem?

What is over-propped and under-propped?

 

[JB]

Re: What could be the problem?

Check the stator and carb link for free turning and spring return, Shoe.<br /><br />Getting full torque when you open the throttle requires full advance of the ignition as well as opening the butterflies in the carbs.<br /><br />If either sticks and then slowly catches up you will get exactly what you describe.<br /><br />Good luck.

 

[imstillatwork]

Re: What could be the problem?

What is over-propped and under-propped?<br /><br />A boat is run full throttle a lot. so when at full throttle, you want the rpms to be within a recommended range for your motor. To do this, you match the propeller to your boat and motor so that the combination at full throttle will run in the desired rpm range.<br /><br />more pitch on the prop is harder for the motorto turn, but potentialy faster if your motor can spin it. a underproped boat will take forever or never plane, because the motoris at WOT, but the prop is not moving enough water to plane.<br /><br />since yours does plane and take off like mad after that, you are trying to move to much water for your motor, making it take a long time to plane, because your motor doesn't have quite enough power to get it there quick. when your motor eventually gets the boat to plan, a lot of resistance is lost, and it takes off.<br /><br />More experienced here can correct me and say it simpler probably.

 

[imstillatwork]

Re: What could be the problem?

that is, of course, if that is even the issue here.

 

[The Shoe]

Re: What could be the problem?

Weather didn't permit me to get out on the water this weekend <br /><br />I'm eager to get to the bottom of this!

 

[Chesapeake Explorer]

Re: What could be the problem?

My 88 90 hp did the same but only on starting out from the marina after starting and warming up a bit. I had a air leak on the VRO system , check to see if all the plastic hose clamps are tight. That said it only did it on cold start after a good warm up it quit. I mixed 50-1 so the air leak did not affect oil mix.. VRO was fuel pump function only.

 

[The Shoe]

Re: What could be the problem?

Ok, finally got to take the boat out and check the RPM's at WOT....5,800<br /><br />Now what? I guess it is propped correctly...

 

[Walker]

Re: What could be the problem?

It could be the angle of your transom. I have seen some boats that required beveled shims between the top mounting bolts to get the motor at the right angle to the hull.

 

[rayjay]

Re: What could be the problem?

Are you just hammering the throttle all the way open or are you smoothly applying the throttle over about a 5 to 10 second time frame ? Plan B is better.<br /><br />Is the motor picking up revs and the boat not going anywhere or is the motor gasping or refusing to rev?