77 Evinrude 115 HP running strangely

[RustynHouston]

this is my first boat and outboard experience-<br /><br />just purchased 77 Evinrude 115 HP that had carb overhaul and new water pump before I got it. I just put on new fuel pump. (compression same in all cyl and good)<br />while running across the lake at set throttle, the engine sounds like it revs up for a while then revs back down. Speed remains the same with no noticeable performance shift. Engine idles and shifts fine. Its almost like the clutch is slipping, but these are direct drive once they are in gear. There is no "clunk" or jerking when the rev up and down takes place.<br />any ideas out there? thanks!

 

[ob]

Re: 77 Evinrude 115 HP running strangely

Check to insure your prop hub isn't spun.You can do this by close visual inspection or making two relation marks on the prop and hub and see if they stay aligned after experiencing symptom.Good luck.

 

[RustynHouston]

Re: 77 Evinrude 115 HP running strangely

thanks OB. You are an immense help along with this forum....aint the internet grand?<br />I bought a Seloc manual and they don't talk about the "prop hub spun" issue, except for a brief mention. <br />After your naming the probable cause, I researched the forum and self educated on it. Am I correct in that all I have to do is repair or replace the prop?<br />If that's true....I'll be a happy camper!<br />Thank you again.

 

[Walker]

Re: 77 Evinrude 115 HP running strangely

Rusty, from what you describe I'd say you are correct. But you need to be sure its your prop first before repairing it. Do the mark thing OB mentioned. One other thing might cause your problem. that is having your prop too close to the water surface. Motor mounted too high or trimmed out too much.

 

[Joe Reeves]

Re: 77 Evinrude 115 HP running strangely

Usually props, once they have slipped at a high rpm usually do not grab again until the rpm (throttle setting) is dropped to a great extent. If this problem was due to a slipping prop, the rpms should increase beyond the present set rpms and the craft should drop in speed.<br /><br />If I understand you correctly, the problem is a slow up and down surge. That should affect the rpms and the forward speed, however possibly it is not a major surge problem.<br /><br />I've found that type problem is usually caused by a air/fuel leak somewhere between the fuel pump and the fuel supply, or a mild fuel restriction. Check the O Rings if you're using snap on fuel connectors, all hoses etc.<br /><br />When this problem takes place, have someone pump the fuel primer bulb, acting as a manual fuel pump. If this eliminates the surging, the problem is fuel related.

 

[RustynHouston]

Re: 77 Evinrude 115 HP running strangely

Joe,<br />The first problem I had with the boat (I consider it minor) was the squeeze bulb going flat due to faulty quick disconnect(S) in the fuel line. A $10 Walmart replacement hose between the fuel tank and the Evinrude corrected that. The bulb was the first thing I checked.<br /><br />I may be wrong, but the boat doesn't seem to slow down when the motor revs.If I do, in fact reduce the throttle, she seems to "get a grip" faster, but I let her be once and she still came back and "gripped" (How about these non nautical terms?)<br /><br />My prop is well under the bottom of the boat so I ruled that out. <br /><br />Now when turning sharply, the experience of losing grip is called cavitating? Then if going straight, the experience is called ventilation? I went from a 17 pitch to a 19 pitch. (115 HP on alum 18' semi V hull)If the hub is not spun, I will consider going back to a 17 pitch to see if the problem goes away.<br /><br />I am going to mark the prop and hub, then when she revs and slips, I'll check for a change.<br />If that doesn't show a change, I'll try a 17.<br /><br />thanks much!

 

[Joe Reeves]

Re: 77 Evinrude 115 HP running strangely

The "Flat Bulb" scenario is caused by a fuel restriction. The hose replacement may have been a partial fix. If you're using a built in tank, see the following.<br /><br />(Fuel Anti Siphon Valve)<br />(J. Reeves)<br /> <br />Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vaccum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.<br /> <br />NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models. <br /><br />The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

 

[ob]

Re: 77 Evinrude 115 HP running strangely

Originally posted by Joe Reeves:<br /> The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction.

I must have missed something either in this post or another one.

 

[Joe Reeves]

Re: 77 Evinrude 115 HP running strangely

OB.... That horn warning mentioned would pertain to the V6 & V8 models.<br /><br />I'm wondering if he has a partial fuel restriction.

 

[ob]

Re: 77 Evinrude 115 HP running strangely

I understand now Joe.In was intitially stumped and recommended checking for spun hub because it sounded like a possibility.The fact that he mentioned changing props from 17" to a 19" (possibly used) makes me even a bit more curious as to whether his issue is prop related.<br /><br />I am also aware that a partial lean out from a fuel restriction can cause a rise in rpms as he is experiencing.<br /><br />I wish him luck in finding the problem ,whatever it is.

 

[Joe Reeves]

Re: 77 Evinrude 115 HP running strangely

OB.... I'm also curious about the prop. I've never heard of one acting that way but I'm not that old whereas I'm not able or willing to learn something new.

 

[Walker]

Re: 77 Evinrude 115 HP running strangely

Another thought. You may be dropping a coil. At an easy cruise speed with light load you may not notice much change in performance when it happens. I'd pull all the coils off, inspect them for cracks and leaks, and clean the ground straps and where they ground to the block.

 

[RustynHouston]

Re: 77 Evinrude 115 HP running strangely

Back when I experienced the fuel pump bulb collapse, I did have the lean fuel rev you mentioned above. The rev experienced now is similar but the bulb is not collapsing. Perhaps I still have a fuel starvation problem. <br /><br />The newly installed 19 pitch prop was picked up as rebuilt at a Houston reputable prop shop.<br /><br />Concerning the coil drop....what would be causing the rev? A coil going out would be a reduction in the spark intensity wouldn't it? Would this cause the rev?<br /><br />I will be marking the prop/hub to check for spin, checking coils for leaks, cracks, grounding, etc, checking fuel starvation possibilities - all this weekend. I'll report findings Monday. Thanks guys.

 

[RustynHouston]

Re: 77 Evinrude 115 HP running strangely

severe case of the flu has postponed my boat activities......will advise later

 

[RustynHouston]

Re: 77 Evinrude 115 HP running strangely

well I finally got the time to check out the spun hub theory and the WAS the problem. Replacing the old ss 19 pitch prop with my spare aluminum one (19 pitch)fixed it. I'll be taking my ss prop in for a repair. I have learned that the 19 pitch means faster forward speed even at dead slow and I don't think I like that. I can see in close quartered marinas, I like to go slower. I'll go back to a 17 pitch if my prop shop has one.<br />Thank you again! <br />Thank you for the help

 

[ob]

Re: 77 Evinrude 115 HP running strangely

Glad you found your problem Rusty.Whatever pitch you end up with ,make sure it allows the engine to reach its recommended wide open throttle operating range.On your engine anything below 5500 rpm will be overpropped.The higher the pitch number ,the lower the rpm capability.

 

[RustynHouston]

Re: 77 Evinrude 115 HP running strangely

Well maybe I HAVEN'T solved my problem after all:<br />I took the 19 pitch prop back to my prop shop and they said it didn't look like it was spun. They asked what RPM I was running and I dont have a tach so I couldn't say. After some discussion, they recommended I install one ($120)so they had more info to go on. They asked me questions as to what were the water conditions when I had "the blow out" (they called it)and I remember it was choppy. My most recent test was on smoother water, but all my troubles began with the 19 pitch SS (choppy with 3 on board - not full throttle but clipping along nicely) and I didn't notice any "slippage" with the 19 aluminum spare on flatter water - no passengers. <br />This "blow out" phenom??? is this leaving the water? air borne? or just air bubbles around prop?? and can this be caused by too much pitch? cause nothing else has changed and my prop is well down beneath the boat and worked fine before.???

 

[Basscat 1]

Re: 77 Evinrude 115 HP running strangely

Is it just me or does it sound like the boat may be porpoising (sp?) Does it seem like the boat may go airborne for split second or does it bounce when you hit even the smallest of waves?<br />Just a thought. If so you may want to invest in a fin. It will slow your boat down on top end, but it will certainly handle better.<br />Just curious. What size boat do you have that 115 on?

 

[fireman57]

Re: 77 Evinrude 115 HP running strangely

Sounds like a job for NautiJohn.

 

[RustynHouston]

Re: 77 Evinrude 115 HP running strangely

It's an 18' aluminum Waco (looks like the Tracker deep v model those northerners use to troll for walleye.<br />No sir I'm not bouncing or porpoising at all. I'm not leaving the water either.