WOT RPMs 77 Evinrude 85 hp (revisited)

[jmcgill89]

Thanks to everyone on helping me find out why my Evinrude is turning only 4500 WOT RPMS.<br /><br />As per Dhadley's advice, I checked the throttle linkage. It seems that the arm is not completely touching the rubber stop. How should I adjust that?<br /><br />I tested the compression this afternoon (it was cold, but I had no option due to the Hurricane Ivan). My compression was about 118 on all cylinders, maybe 2-3 lbs variation.<br /><br />I also checked my prop....it has no numbers posted on it....all it said was "9517"<br /><br />Any other advice about this?<br /><br />Joe

 

[Mercathode]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

jm <br />Make sure you do not have a damaged prop. Check and make sure you have not gained any weight in your boat suhc as a live well that has filled and not drained. Often these can hold many gallons and cause some RPM loss. You may check your tach as well. Check how your boat is loaded i.e. is your load in front causing more drag. You may check your tilt pin if you don't have trim. Move the pin to maybe the 3rd or 4th position. whew! Good Luck!

 

[jmcgill89]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

The Prop is in perfect shape....looks basically new.<br /><br />I'll check the bilge, but it doesn't seem that there's much there.<br /><br />It was turning 4500 with 2 people in the boat, and it turned 4500 with 5 people in the boat. I'll check the pin.<br /><br />Concerning the "cavitation plate", what is that?

 

[G DANE]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

"Cavitation Plate" , which really is an antiventilation plate, is the largest horizontal plate above propeller. Motor should be mounted so high on boat that this plate is level with or 1" above a straight board held against buttom of boat. The higher you get your motor, the less drag will the lower unit cause in water. Beware of loosing cooling water pressure, if motor is lifted too high, though.

 

[jmcgill89]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

Well, I looked at the area where the cavitation plate should be. It seems to me that there are 2 relatively large horizontal plates...one right above the exhaust and another above that. Which is the cavitation plate?<br /><br />Also, which "hole" should I use for varying the motor angle? It's in the 3rd right now.

 

[G DANE]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

The antiventilation plate is the one right above propeller. You have to do a couple of trials to find out which hole gives you the best speed and still enables the prop to bite properly during hole shot, depends of boat transom. You lift the motor by using the next lower set of holes in the transom mounting bracket, there should be 3 or 4 sets of holes in upper pair and a long slot in lower. Do a search here on post containing word X dimention or "lifting motor" - you will find lost of good advise. Dhadley and Kenny has done a lot of experimenting.

 

[jmcgill89]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

When I look at my motor, it is difficult to see, but I think that the cavitation plate is somewhat lower than the bottom of the boat. That being said, the motor clamp is resting on the transom right now, if I lift the motor any, it will create a gap on the top of the "clamp". <br /><br />Also, the last time I had the boat out, I noticed that when I was running at WOT and made a sharp-ish turn, the rpms would go down until I straightened again.....what could this be, and could it be related to my WOT problem?

 

[ob]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

jmcgill89,What you are refering to as the motor clamp does not have to rest on the top of the transom.The vertical weight of the engine is contained just fine by the bolts thru the transom bracket.With that said,make any height adjustment necessary to attain optimal engine placement with respect to the anti-ventilation plate and the boat bottom.I'm not sure what the 9517 translates to on the prop you're running ,but I'll se if I can find something.Prop pitch is also a very crucial factor in engine performance on a given boat and it would be beneficial if we all knew which one you're currently using.Also ,post the style ,length , and or approx dry weight of the boat this engine is pushing.That also matters.

 

[jmcgill89]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

The boat is a '77 Glastron "semi v-hull", 17' boat. I think the approx dry weight is about 1100 lbs.<br /><br />Before I go moving the motor up or down, I need to be sure how to measure where it is NOW in respect to the bottom of the boat.<br /><br />No doubt the Prop is an "off brand".....I don't have the bankroll now to get a new one.

 

[Solittle]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

Joe - You should be getting 5000-5500 rpm out of that motor. You can confirm by looking in the shop manual.<br /><br />The cavitation plate should be even with or 1" or so above the bottom of the boat. It can be measured by putting any flat surface (like a yardstick) along the bottom of the hull and measuring the difference above or below the cavitation plate. Move the motor up or down as needed. Then test & adjust as needed.

 

[jmcgill89]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

I'll give that a shot. The Cavitation plate is definitely BELOW the bottom of the hull right now....so I guess I should move it up a bit.

 

[jdstephwacotx]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

Excuse me for butting into the conversation but.....<br /><br />When you guys say 'up' do you mean changing the height of the motor on the transom itself? Or 'tilting' the prop toward the sky and putting the pin up near the motor clamp in a new hole?<br /><br />If you mean the latter....is the fact that the motor seems to rest at an angle a problem? Or does this all work itself out under load?<br /><br />Thanks for the help.

 

[ob]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

jdstephwacotx,By raising up, we are in this case refering to adjusting the height of the motor on the transom itself.

 

[jmcgill89]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

Say I raise the motor about 1" on the Transom. How much could I expect that to improve my RPMs? That's my real issue here....I want to get the WOT RPMs up to 5800. I know that my compression is fine, but that still doesn't rule out bad/weakening coils and/or ignition problems.<br /><br />I basically need to gain 1000 RPMS

 

[ob]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

Expect a wot rpm gain of about 100 - 150 per hole.Once you've reached the optimal height that engine can be raised without experiencing excessive ventilation while executing tight turns on plane,the rest is down to engine performance and prop selection.Tilt/trim angle also play an important role in the rpm capability ,however you'll need to know and have a feel for the boat to maintain good control when trimmed out fully.

 

[jmcgill89]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

My main problem is I don't know ANYTHING about boats, cavitation, ventilation, etc, etc.<br /><br />Which trim/tilt angle is right?<br /><br />I can repair motors all day long, but these heights and angles have me a bit flabbergasted. Couple that with the fact that I can't get to the lake right now to to test things out. I'll probably have to wait for next spring to do anything meaningful.

 

[Boilermaker]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

What gets my attention is the fact that he said>>><br />"...It was turning 4500 with 2 people in the boat, and it turned 4500 with 5 people in the boat."<br />I may have missed something in an earlier post, but maybe we should find those missing RPM's before making changes to his setup.<br /><br />jmcgill89, how does the bottom of your boat look??? Is it a trailer boat, or kept in the water>>>marine (salt or fresh water) growth on the bottom can have a drastic amount of drag to it. Also, any blisters could cause problems with water infiltrating a core on composite type construction (altough I don't think the '77 Glastrons had a balsawood sandwiched layup)<br /><br />You already ruled out any problems with a damaged prop, and that the compression is good (all cylinders are even).<br />How do the spark plugs look??? Are they all the same???Do they have a brown coloring with a bit of oily residue???or are they a black oily/carbon mess?? Maybe yours are whiteish and dry>>>Not a good sign by the way.<br /> Do you have an inline fuel filter>>>if so change it. Check the fuel filter screen at the fuel pump under the cowling. (Its on the port side of the engine>>follow the fuel line from the connecter to the pump & unscrew the large knurled screw in the middle of the pump.You will need to carefully remove the screen from the cover>>>it will trap fine particals on the COVER side, so you have to remove it to check. <br />You may also want to check to be sure that there is no kink in the fuel line from the tank. There may also be a screen on the fuel pickup tube in the fuel tank itself. If its a built in tank it has probably been in there for 27 years now and may be clogged>>>if you can unscrew it to check, do it. Also check to make sure the tank is venting well with no obstructions. The last thing you want is to have a fuel flow problem and run the engine lean>>>on a 2 cycle engine thats a quick death>>>remember the lubrication for the entire engine is in the gasoline. A low fuel flow = a low LUBE flow!<br /><br />Is there anyway you can see below the deck, and check the flotation foam??? It may have become waterlogged. It can carry a LOT of weight there.<br /><br /> Did you add anything to or change anything in the boat since you were getting 4500rpms with 5 B.O.B.??? And do you know what your lightly loaded boats WOT RPM's were before this problem???<br /><br />I would find the reason for the loss of RPMs before making any changes to the set-up>>>Then you can fine tune>>>as I have learned here and from my own mistakes>>>ONE CHANGE AT A TIME!!!<br />GOOD LUCK

 

[jmcgill89]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

Well, I know that the tank is not clogged, but I will check the fuel filter. I also know that the fuel line is not kinked. <br /><br />I don't know how to check the venting of the tank.<br /><br />As for the spark plugs, they're brown with some oil on them. They're brand new, and only have been run once, so they're not an indicator....the old plugs were darker brown and oily. Definitely not running overly lean.<br /><br />The boat is trailered, and the bottom is in fine shape for its age...hardly any scratches. The Previous owner replaced the floor and didn't leave great ways to view the bilge....thus, I don't have a really good way to check the foam. I don't even know where it is. This is our first boat. All I can go on is the Previous owner who used it for 17 years without issue.

 

[Boilermaker]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

OK>>but did YOU own it when it would do 4500RPMs with 5 on board???<br />Do you know what it turned with just 1 or 2 people on board???<br />Has ANYTHING changed since then???<br />The vent would show up as a problem with the primer bulb collapsing when running>>>or a slight sucking sound when you remove the fuel fill cap. But it sounds like your OK with your fuel flow by your plugs.>>.check the screen in the pump anyway.

 

[jmcgill89]

Re: WOT RPMs 77 Evinrude 85 hp (revisited)

No problems with the vent.<br /><br />It ran at 4500 with various loads when I was operating it...on the same day, I had it out with 2 and 5 people, and it turned 4500. I didn't know what WOT was when I bought the boat.