Do engines with low compression usually run smoothly?

[fishndvm]

Just curious. I have been looking for a larger engine for my J12 Carolina skiff, as the 15hp motor (Force 1991) I matched it to just won't plane it, let alone run it at a reasonable speed. Over the past couple of days I have been informed by a number of Carolina Skiff owners that the 15 should push the boat with a couple of people and gear with no problem. The engine seems to run perfectly in my opinion, but I'm just wondering if it could have low compression and still run like a charm. One gentleman suggested that the way horsepower was rated in 1991 is different than the way it's rated today, and that it may be closer to a 10hp than a 15. Any thoughts? Thanks.

 

[LubeDude]

Re: Do engines with low compression usually run smoothly?

Its probably just over propped for your aplication.

 

[fishndvm]

Re: Do engines with low compression usually run smoothly?

Sorry LubeDude...I'm a little new at this. I'm not sure what "over propped" means, but I assume you mean that there probably just isn't enough engine for the job. If not, what exactly do you mean.

 

[gsbodine]

Re: Do engines with low compression usually run smoothly?

he means that you don't have the right propeller for what you're trying to do with that motor. Try reading the Prop FAQ or wait for walleyehed or others to help you. <br /><br />Here's the link, actually:<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000030;p=1#000000 <br /><br />I would help if I could, but I just listen to these guys.

 

[roscoe]

Re: Do engines with low compression usually run smoothly?

Over propped - the propeller has too much pitch ( refers to the angle of the prop blades)<br /><br />A lower pitched prop provides more "bite" and power to plane a boat. Kindof like using a lower gear in a transmission to get up a hill.<br /><br />For your reading pleasure:<br /><br /> http://www.boat-props.com/prop_info_2.cgi?page=pitch

 

[rodbolt]

Re: Do engines with low compression usually run smoothly?

hello<br /> if you suspect the motor is not making powewr have the dealer run it up on the test wheel. if it will turn in the proper RPM range on a test wheel then your going to deal with a prop problem or you just have to much boat for the motor. there is no such thing as a "standard" prop. just like eyeglasses each engine will need the prop properly "fitted" for the application.<br /> good luck and keep posting

 

[fishndvm]

Re: Do engines with low compression usually run smoothly?

Thanks for all your help. I found a buddy in the area with a 15hp engine. I intend to put that motor on the boat and see how she goes. If the boat moves well, I'll try to figure out what's wrong with my engine. If it doesn't move well, I'll find another engine with more zip.

 

[cobra 3.0]

Re: Do engines with low compression usually run smoothly?

Those links may be a lot of technical jargon for a newbie. What is boils down to is if your prop for example, is stamped 9 dia. x 11" pitch, a lower pitch prop like a 9" dia. x 9" pitch will give you more torque and power for your heavier boat.<br /><br />Prop selection becomes very significant with a marginally powered boat.<br /><br />If your two stroke has never been decarbed with Seafoam (a decarbing spray), this can really bring your motor back to life too.

 

[Scaaty]

Re: Do engines with low compression usually run smoothly?

Make sure your hull is clean!!! And unload the junk!

 

[CFronzek]

Re: Do engines with low compression usually run smoothly?

How good is the motor? Has it ever had the cylinder pressures checked? If the motor has been used hard it may not be making sufficient HP any more. Changing props on a motor that's over the hill won't get you much. <br />Also, the ability to plane is affected by what's in the boat. A boat with two 150 lb. guys in it might pop right up on plane. With two 300 pound guys and a couple of 12-packs it might not plane with twice the HP.<br />Don't get sucked into speculations about the manufacturer's HP numbers. Concentrate on making sure that what you have is up to snuff mechanically. <br />Charlie

 

[FlyBoyMark]

Re: Do engines with low compression usually run smoothly?

That particular motor was one of the fastest in the early 90's and one of the better motors made by Force/Mercury. At full throttle with the proper prop its supposed to turn about 6,000 RPM @ WOT. There are two props available for that engine; a two blade 8" pitch for bigger loads and a 3 blade 9" pitch for lighter loads(under 600 lb gross). That engine is also quite contankerous to a dirty carb or plugged filter on the inlet side of the fuel pump(remove fitting to extract filter, very tiny screen) The spark advance setup on that engine can easily be messed up by some unknowing individual messing with the set screw on the spark advance idler cam roller adjustment linkage. I own one of these engines on a SeaNymph 12R and with my 240lbs my son @ 160 lbs, boat @ 100 lbs, motor 70 lbs, battery 20 lbs, trolling motor, gear and ice chest and 3 gal of fuel we get 24 MPH. And 27 MPH alone with no gear. Mine is a Sears version, 1989 vintage. There is a posibility that someone swapped the cowel on you and its only a 9.9 HP. Need serial numbers to verify this. On your particular engine, the only difference between the 9.9 and 15 hp is the carb and induction manifold.