High RPMs - Update for DHadley

[rboat99]

I was talking to a Johnny/Evinrude mechanic and was talking to him about my recent fuel problems at 6000 RPMs. He said that my boat should only be running at about 5500 RPMs. I told him that my OMC manual said that my RPM range was 5000-6000 RPMs. He said, "Well if that is the case I guess 6000 is ok, but I think 5500 would be better." He suspected that I may have a worn prop causing my RPMs to be that high.<br /><br />So I ended up fixing the fuel problem last night, and when I tested the boat on the river -extremely calm waters, ~10 gallons of fuel, no ice in the cooler, just me and my wife - I was getting up around 6400 RPM (just below it). So is that too much, or is it because I had a light load?<br /><br />It looks like the original aluminum prop, 13x9 I think. It has some wear, but not that much. Should I think about changing it?

 

[Dhadley]

Re: High RPMs - Update for DHadley

Do you mean a 13x19?

 

[kennedyt]

Re: High RPMs - Update for DHadley

Over rev is real bad for 2 strokes. Has it always run this high? Could be lots of things. <br /><br />WOT mark in correct position on throttle linkage? <br /><br />Prop sliping? <br /><br />Tachometer reading error?<br /><br />Don't run it that high until you verify. Remember - 2 strokes die when over-rev'd.

 

[Dhadley]

Re: High RPMs - Update for DHadley

As long as there is a load on it you can safely turn it that high. Some V4 loopers have the rev limiter at 6700.<br /><br />Lets verify the prop size and then the tach settings.

 

[rboat99]

Re: High RPMs - Update for DHadley

I've had fuel starvation problems at WOT ever since I bought the boat so I do not know where it should be.<br /><br />And yes, I meant 13x19.<br /><br />How would I verify the Tach settings?<br /><br />I don't think the prop is slipping because the speed steadily increases as the RPM's do. Tops out at about 30 MPH. Maybe that is not a good indication though.

 

[Dhadley]

Re: High RPMs - Update for DHadley

OK, good info. The tach should be set on position 6. Not 4. I suspect this may be where some problems lie.<br /><br />The 19" pitch is about where we would start but I doubt we'd be anywhere near 6400. In fact, depending on which gearcase your Sea Drive has we might end up with less pitch.<br /><br />If we assume the tach is correct you are over 45% slip at 30 mph. Definately something amiss.<br /><br />Lets look at the tach and make sure its set right.

 

[rboat99]

Re: High RPMs - Update for DHadley

OK, is that just a setting on the back?<br /><br />Also, what does 45% slip mean?

 

[Dhadley]

Re: High RPMs - Update for DHadley

Yes, its a setting on the back of the tach.<br /><br />You are losing, in theory, about 45% of your forward thrust. You want to get down under 15% for sure. More if possible. Its a bit harder with a Sea Drive or I/O than an outboard.

 

[rboat99]

Re: High RPMs - Update for DHadley

So what speed would I be running if I was under 15%? I actually didn't have my GPS or Depth finder on the boat when I tested so I am not completely sure of my top speed. I was just trying to recall when the boat was running a little better and I thought it was around 30MPH. I could be off by a few MPH though. Sorry. I am taking her to Egmont Key on Friday so I will verify max speed then.

 

[Dhadley]

Re: High RPMs - Update for DHadley

Thats good. Lets look at the tach setting so we know your numbers Friday will represent a good baseline.

 

[rboat99]

Re: High RPMs - Update for DHadley

OK, thanks a lot for your help.

 

[rboat99]

Re: High RPMs - Update for DHadley

BTW DHAdley, did you see my other post on the reg/rect gray tach wire? Do you know why it it is wired that way?

 

[Dhadley]

Re: High RPMs - Update for DHadley

I'll go take a peek.

 

[rboat99]

Re: High RPMs - Update for DHadley

Update - I checked the tach and just as DHadley suspected, it was set to 4 instead of 6. I moved it to 6 before I headed out. Now I think maybe my RPMs are a little low.<br /><br />With me and my wife, a couple bags of ice, a few more supplies and about 25 gallons of gas I would say it was a medium load. We were inland, but it was a little rough out due to some thuderstorms offshore.<br /><br />Depending on wind and chop, the boat ran at from 4900 - 5100 RPMs at WOT. Is that too low? At this RPM we ran from 29-32 MPH again depending on conditions, and which instrument I was reading the speed from (the GPS was always higher than the wheel on the depth finder).<br /><br />BTW Dhadley, in my other post, hopefully I explained myself right when I said that the grey tach wire was tied in with the orange black wire - meaning the orange wire with the black stripe. One comes from the stator, and one from the power pack.<br /><br />Thanks again for your help.

 

[Dhadley]

Re: High RPMs - Update for DHadley

Yeah, thats a little low but with a Sea Drive there's not much we can do other than use a lower pitch prop. If it were an outboard we could raise the motor to reduce drag to pick up a few rpm's.<br /><br />Thats good that you tested with an average load. We like to do it that way too.<br /><br />I understood about your wiring. Thats really wierd. The orsnge wire with the black tracer has to do with the SLOW circuit, Quick Start and the rev limiter. I dont know why your tach wire is tied in there.

 

[rboat99]

Re: High RPMs - Update for DHadley

OK, well thanks alot for all the help/advice. I am happy with the way it's running now that I got the fuel problem worked out. The boat has never run more than about 32MPH - at least since I bought it, that's fine for what I do. If I can just get my charging problem taken care of I will be done.