8 hp Evinrude won't plane off boat

[silverwaters]

Just bought an 8 hp Evinrude, used 1994. I was a YachtTwin, but the dealer converted it into a short shaft for me. I saw it run in the tank and it ran great (with the shaft extension still installed). I took it home, put it on a 12 foot boat, and it wouldn't plane off. The motor should easily plane off a 12-foot 100 lb. boat. I could also tell it was not running at full throttle even with the handle twisted to WOT. The higher the rpm, the less the engine would run smoothly and smoke more. At WOT, it ran as if the choke were partially closed. <br /><br />The dealer put a remanufactured prop on this motor because the one it came with was meant for a sailboat motor (probably more pitch, right?) I am thinking this is the problem. The prop will not allow the motor to turn enough RPMs yet it is getting WOT fuel poured into it...it can't burn it fast enough w/o the RPM...causing the poor running and smoking the higher the speed. <br /><br />Any other theories? At low speeds, the motor runs super smooth. It has few hours on it and is in nice condition.

 

[silverwaters]

Re: 8 hp Evinrude won't plane off boat

Oh yeah, the prop the dealer put on it is 8.5" x 9". A quick check on iboats indicates that they offer two pitch sizes...7" and 9". Would a 7" pitch prop solve this problem????

 

[68whaler]

Re: 8 hp Evinrude won't plane off boat

I have an 8' plywood boat that would move along very slowly with the bow in the air with a Rude 7.5, a lad when I got this boat I was heartbroken till I moved my skinny butt up to the middle seat. The RPM's picked up and she about jumped into a plane. Once there I could move back to the rear of the boat. For a 7.5 she really hauled.

 

[silverwaters]

Re: 8 hp Evinrude won't plane off boat

I tried that myself...moving the middle seat...no such luck. RPMs didn't increase and the motor continued to run less than WOT.

 

[Chinewalker]

Re: 8 hp Evinrude won't plane off boat

The problem isn't the prop. I've run the same motor on my 12-foot Duranautic with the same prop and it flat out boogies... You've got something wrong elsewhere in the motor. Check for spark on both cylinders...<br />- Scott

 

[WillyBWright]

Re: 8 hp Evinrude won't plane off boat

An 8 isn't likely to plane a 12' boat. A 9.9 would have a tough time. A 15 would do it.<br /><br />We had a 20' long 7' wide jon boat for delivering piers and lifts. A 5Hp Scott planed that boat off. It was the amount of surface area that did it, sort of a planing surface to weight ratio. You'd probably have an easier time planing a 15' jon than a 12 footer. You'd also have an easier time planing a jon than a v-hull. If you have a 12' vee, an 8 ain't gonna plane it. You might get lucky, but it's a borderline combination at best.

 

[tashasdaddy]

Re: 8 hp Evinrude won't plane off boat

search my post "1960 lonestar 55 15hp rude finished for now". it's 2 1/2 ft longer than yours and 2x the hp. when 1st set up with gas can,battery in front, all it would do is stand up and point the bow to the sky. move gas can to the stearn, installed esy glide stick steering and remote engine control, now it jumps on plane, runs around 25 mph, and likes rough water. it's the best one man boat i've ever had, and my favorite. and i've had many boat big and little over the last 40 years. i'm teaching the grand kids how to ski with it as it has enough power to pull them, but not enough to scare them.

 

[Texasmark]

Re: 8 hp Evinrude won't plane off boat

I had a 12' lake john which was a large 12' john. I could load it down with fishing gear, or duck hunting gear, 3 gal of fuel and myself at the stern. My 7.5 Merc would not only plane it off but run it at a good clip estimated to be 22 to 25 range.<br /><br />Mark

 

[JB]

Re: 8 hp Evinrude won't plane off boat

Check the carb, SW. Sounds like it is 4 cycling at high speed, running too rich. Excess smoke, leveling out below full rpm and burbling sound are the clues.<br /><br />I don't remember if the '94 engine had an adjustable high speed jet, but if it does, turn it in (CW) at WOT, under load, until she smooths out. <br /><br />If there is no adjustment on the high speed jet, it could be a stuck float or bad float needle.<br /><br />Good luck.

 

[silverwaters]

Re: 8 hp Evinrude won't plane off boat

First, I guarantee you that an 8 will plane this boat. Willy, I understand what you saying about a large surface area riding on top of the water easier and giving a higher top speed. But I had a 6 hp Yamaha that would easily plane this boat and a 5 hp Force that would plane it with the gas tank up front.<br /><br />UPDATE - you guys are right...it's not the prop. I tried one with a 7" pitch today. No difference.<br /><br />JB - I think you are right. There is something wrong with the carb. There is no high speed adjustment on it, so the float is probably stuck or the needle is bad. It's funny how well this motor ran just last Saturday, all rpm ranges. Yet, I take it home, plop it on the boat, and have this problem.

 

[tashasdaddy]

Re: 8 hp Evinrude won't plane off boat

taking it home probably shock up the carp in the bowl or tank.

 

[silverwaters]

Re: 8 hp Evinrude won't plane off boat

I hope that is the case. Here are the things I have checked...<br /><br />1. switched to a different fuel tank<br />2. made sure the butterfly valve in the carb was opening fully<br />3. checked to make sure the ignition was advancing to full throttle<br />4. adjusted low speed carb<br />5. tried prop w/ lower pitch<br />6. pulled out choke at WOT to see if it was starving for fuel<br />7. removed spark plugs and cleaned them up<br /><br />NONE of the above made any difference. One thing I did notice...when I removed the spark plug from the lower cylinder, it was wet, after the motor was sitting overnight resting on its back. Any significance?<br /><br />Any quick easy solution to the likely carb problem? I bought this motor from a dealer 50 miles away and it was a consignment deal. The dealer probably will stand behind it (he's a pretty good guy) but I don't want to drive a total of 200 miles if it is something I can fix easily myself w/o getting too technical (I don't want to remove and dissect the carb!).

 

[fireman57]

Re: 8 hp Evinrude won't plane off boat

Redoing the carb isn't a big deal. Just make sure you soak it in a good carb cleaner and blow out all the passages. Get a rebuild kit, if you dealer is that good he might even send you one as they only run about 20.00 I think. I say he might because it might save him shop time. There are plenty of post on rebuilding carbs using the red search feature. Shouldn't take you over an hour. The soaking should take a lot longer.

 

[silverwaters]

Re: 8 hp Evinrude won't plane off boat

The carb is all apart in the garage...can't see anything wrong with it...going to spray out the parts with carb cleaner and air (if I can) and put it back together with a rebuild kit. <br /><br />A part fell off when I was removing the pin holding the float assembly. It is a tiny little screw that has a small wire wrapped around it. I am guessing it is the spring for the float hinge. I will see if I can figure out where it goes...if not, I will be back with pics!

 

[fireman57]

Re: 8 hp Evinrude won't plane off boat

You are correct. Tiny screw with a spring holds your float. You can't see the stuff with the naked eye that will make your day pull a vacuum. I believe that if your carb is clean that you will fall in love with your engine all over again.

 

[silverwaters]

Re: 8 hp Evinrude won't plane off boat

Well...not so, fireman57...<br /><br />Carb is completely rebuilt, new gaskets, completely cleaned. Did it solve the problem. Yes. Sort of. The fluttering at any speed (probably from too much fuel) above idle and not being able to run at WOT is gone. It runs smooth at WOT. I don't know if it is running full RPM because I could only test the motor on the trailer at the ramp (it was dark). However, the fluttering from running too rich is now ever present in the midrange. Can't get rid of it. Open it up to full throttle, the fluttering continues for a few seconds then it clears out and runs smoothly. Back to half-throttle, it runs smooth for a few secs. then it starts fluttering and running rough again. Down to idle, it smoothes right out.<br /><br />I don't have a clue in the world what could be causing this.<br /><br />On this motor, there is a regular screw (not an idle or high speed adjustment) right above the throttle opening. It is part of the top plastic piece that houses the idle speed adjustment and mechanism that opens and closes the butterfly valve. If I play with that screw, sometimes I can get the motor to run smooth part-time. Take the screw all the way out (which you would think would give it more air and cause it run lean), it flutters at all speeds except idle. WHAT IS THIS SCREW FOR??? (by the way, it is a 1994 Evinrude 8 hp).<br /><br />Any, any, ANY possible ideas what the problem could be with this motor? The only thing I haven't tried is new plugs, but I don't think that is the problem. After all, it starts easy and idles beautifully. The problem is midrange.

 

[silverwaters]

Re: 8 hp Evinrude won't plane off boat

JB describes the noise as "burbling". I describe it as fluttering. The motor is not getting the proper amount of fuel...it is getting too much.

 

[Chinewalker]

Re: 8 hp Evinrude won't plane off boat

Have you checked for spark on both cylinders? Compression? You described one plug as being wet - classic symptom of not running on one cylinder. Check for spark in the open air AND while running. Try starting the motor with one wire removed and grounded, then try the other...<br /><br />- Scott

 

[silverwaters]

Re: 8 hp Evinrude won't plane off boat

There is spark at both cylinders. I checked that already. The fuel on one plug (bottom cylinder) was after the motor was resting on its back all night and hadn't been run yet. I am going to put in a fresh set of plugs tomorrow and see what the result is.

 

[JB]

Re: 8 hp Evinrude won't plane off boat

Don't read too much into a wet plug.<br /><br />The engine did not stop instantly when you killed it. It turned a bit more, perhaps pumping fuel mix into a cylinder where it did not get burned.