Am I expecting too much out of a 10 HP motor?

[eavega]

Hello to all

I have a QD-21 (Johnson 1960 10 HP Sea Horse) that I acquired about two months ago. I have done the following work to it:

1. New spark plugs
2. Impeller replacement
3. Cleaned and rebuilt carb
4. Changed LU oil
5. Inspected coils
6. Gapped points

Apart from that, I did some other necessary repairs like replaced the recoil starter spring (snapped) and the prop nut (damaged it while trying to remove the prop for inspection)

I ran it in a barrel to make sure it would start and was pumping water and cooling properly.

Last weekend I finally put it on the back of my boat and put it on the lake to make final adjustments on the needles, and just to see how it would perform.

I have a 14' Valco semi-vee fishing boat. Plate on the back says its rated up to a 25 HP motor, max weight in the boat of 950 Lbs. The boat itself is probably about 150Lbs-200Lbs. I would estimate I had about 500 Lbs to 600 Lbs in the boat (myself, electric trolling motor plus battery, seats, 4 gal fuel, tools, and fishing gear), heavily weighted to the stern (fishing gear, 3 gals of fuel and some of the tools were in the bow, everything else was in the back)

The motor started cold with choke pulled out in 3 pulls (primed until the squeeze bulb got hard). I shut down and restarted the motor probably a half-dozen times, longest interval between restarts may have been about 10 minutes. Longest interval of running the motor without shutting down was probably about 20 minutes. Started on first pull on each of the restarts. Motor smoked some at first (expected, b/c I had sprayed each cylinder with Deep Creep back when I was working on it), but by the time I was heading in, it wasn't smoking any more than I would expect from a 2-cycle motor.

Now, here's the problem; with the throttle twisted as far as it would go, the boat mustered a whole 6 MPH, measured with a GPS. That was after I trimmed the motor up to try and get the bow down a bit. The motor ran smooth, would rev up and down in response to twisting the throttle, did not bark, hiccup, or hesitate.

As the title implies to my post states, though, am I wondering if I am expecting too much out of this motor. Should I be happy that it is running smoothly, but doesn't pull the boat very well? What are some of the possibilities for smooth running with no power?

My next steps:

I have a "tiny-tach" on order, b/c I don't know what the RPMs actually were on the motor at WOT. That is my next check.

When I have it on the water again (next weekend), I am going to check to see if I have a cylinder that is not firing. I checked the spark when I changed the plugs, and I get a nice blue-white spark. Given that is is running fairly smoothly, I would think that both cylinders are firing. Granted, I did not change out the coils and points, but the coils did not appear cracked or even old, and I was getting good spark. I haven't changed the coils b/c this involves having to get a harmonic puller, and the budget is a bit thin for one of those plus the parts I need, and I was avoiding it if possible.

The prop on the motor is probably the one that was originally on the motor when it rolled out of the factory in 1960. There is nothing obvious with the prop, but you can imagine is has some wear on it.

Anyway, any insight, observations, or reality checks would be appreciated. Thanks for reading my long post.

-Eric

 

[tysonnathan]

Re: Am I expecting too much out of a 10 HP motor?

Was the boat planed out, or just plowing through the water? I would expect more than 6mph from that rig. I have a 14' Sears v-hull aluminum boat, and i can do well overs 6mph with an 8hp mariner with two people, trolling motor and fishing gear... I dont know where to tell you to start looking as far as possible problems go... just thought my rig might give you something to compare to

 

[CATransplant]

Re: Am I expecting too much out of a 10 HP motor?

Couple of things you might want to consider:

It sounds to me like your outboard is probably running OK, so let's look at a couple of other things.

Frankly, you're at a marginal horsepower to plane that boat out. Weight distribution and trim angle are going to be key in getting it to plane for you.

Check where things are in the boat. You gave a pretty high number for loading, and said it was stern heavy. Try moving the battery up front, near the front seat. Tools, too, and get your tackle at least near the center of the boat. You'll be amazed at how much difference weight distribution makes. Consider finding a way to move yourself forward, too. Even six inches can do the trick.

Next, experiment with the tilt pin. On that semi-V design, you have to get the boat riding on the flatter part of the boat. The V will plow through the water and contribute more drag. You may have the motor tilted too far in toward the transom, which pushes the bow down.

I know that sounds wierd that you'd move weight forward to get the weight off the stern, but it works. Then, with the motor tilted to the right angle, the bow will ride a bit higher and the boat will plane.

Since this boat is rated for 25 hp, you're on the edge of what will plane it, at less than 50% of rated power.

I have a 12' semi-V aluminum boat, rated for 10 hp. I have a 6hp on the back, with all the junk you have in the boat, as well. To get mine to plane, even with 60% of rated power, I had to move the battery and fuel tank forward of the middle seat and move my rear seat about 6" ahead by building a box for the seat to mount on. Even so, if I put too much gear in the boat, it will bog down and refuse to plane. If I take the trolling motor, battery, and everything else I don't need out of the boat, it planes nicely, and at about 17 mph. With all the gear it in, it takes a little time to get on plane and goes about 14-15 mph.

Finally, if you can swing it, consider going up to 15 or 18hp on that boat. 18 would be ideal, and there are lots of those around. Then, it'll plane just fine, and do well over 20 mph. You can probably find one about the same age as your 10hp for about what the 10 is worth. Maybe even a trade.

 

[R.Johnson]

Re: Am I expecting too much out of a 10 HP motor?

I always have to chuckle when people insist on laying down a sub-floor, and carpeting their fishing boat, talk about adding weight.

 

[fishrdan]

Re: Am I expecting too much out of a 10 HP motor?

CATransplant is right on the money, balance the boat and trim the outboard.

I have a 7.5HP on my 14' jon and it flies when loaded up with 400+#, throw on another 200# (max weight) and it's a bit doggy, but still gets up on plane. When I bought the boat the 1st thing I did was to load all my gear up and take it to the river for some testing of where the load needed to be placed. I have 200# (batteries, anchors, fuel tank) under the middle seat of the jon, this load is centered at 7'9" from the transom. I know my boat is a different hull design than yours, but this will give you some direction to head.

I don't think decking a boat is bad,,, as long as it's done properly. I low decked my jon boat with 3/8 ply, 1" stringers and foamed underneath. This added 40# made the boat feel solid under foot and significantly dampened the tinny hull noise. The benefits of the decks are well worth the extra 40#.

 

[eavega]

Re: Am I expecting too much out of a 10 HP motor?

Gents

Thanks for the replies. I guess I never really considered that the boat is rated for 25 HP. The hull is old, and I really didn't want to stress it, which is why I went with something on the smaller size. Good thing, b/c I had been negotiating pretty hard for an 8 HP motor, which eventually fell through.

I guess my first step is to visit the weight and balance issue. I had a suggestion in a previous thread about mounting the trolling motor off of the bow, so I'll start there, thus sliding the 100 Lbs of trolling motor and battery into the bow.

Now trying to move the fuel tank into the middle, will that affect how the fuel feeds into the motor, i.e. am I going to have problems if the fuel has to travel further than the 5 feet of hose it currently travels through? My vague recollection of fluid dynamics tells me that the fuel pump would have to work harder since there will be more fuel (and thus more weight) in a longer fuel line, but that change in weight may be negligible.

I also thought about getting a tiller/throttle extension put on the motor, so I can slide my non-inconsiderable weight forward closer to the middle seat, but the only concern I have is that the gearshift and the kill button are on the motor itself. I guess I can rig up some kind of extension rod for the gear shift, since there is a slot on it which I would imagine is there for just such a reason, but for the kill button, what would work?

Thanks again for the responses, and in the meantime if I can find someone that has an 18 HP motor they would like to trade for a working 10 HP, I can explore that route too. It just kinda hurts, because I am rather proud of the fact that I got this motor working again.

-Eric

 

[CATransplant]

Re: Am I expecting too much out of a 10 HP motor?

You don't need to move your seat that far forward to make a difference. In fact, moving mine forward made it a lot easier to steer the boat, since the seat was in the center and sometimes interfered with the tiller handle. I only moved it about 6" forward, and I steer now just by hanging my arm over the back of the seat. Very nice.

As for the fuel, I have 10' of hose on mine, with the bulb near the tank. No problems with the fuel pump on my 8hp. What I did, though, was mount the tank at seat height, so the pump doesn't have to lift very far. I actually built a 10" wide shelf between the rear, middle and front seatst, put a little frame for the tank to sit in, and two screw eyes, where I run a bungee across the tank for stability. It can't move. I also mounted my tackle box on that shelf, opening up the floor of the rear of the boat. Works very nicely.

 

[CATransplant]

Re: Am I expecting too much out of a 10 HP motor?

Oops! Double posted.