15hp mercury help needed bad

Post before mine is 4 months old...

Good info Par and RF!

 

btw guys I look at any replies to my posts regardless or age
thanks again

 

Bump. I just purchased a dinghy with a 15hp mercury 4 stroke. 2009 or 2010 model. I have also heard that the 20s are the same engine. It would be great if I could bump it up to 20hp for under $500. As stated the displacement and all other specs except hp are identical on mercurys site. Any information you guys have on part numbers would be appreciated.

 

To find out why the 20 has more hp one can check part numbers of various parts like the camshaft. For example if the camshaft is different it probably provides different valve timing and/or lift. Carb jets and many other parts may tell the story and/or offer solutions. Check the engine speed for rated power. It's possible both engines are the same and only spec'ed for power at different engine speeds. But all this sort of thing may/will/could be quite time consuming. At lower rpm the 15 hp probably has the same ability to push a boat as the 20 and it may have the same ability to get a boat on plane w a normal prop. The extra 5hp is probably all at the very top end. I recommend for you to try a lower pitch prop to get the thrust you are looking for.

 

or even a restrictor in the throttle body /mount but its usually a smaller carb

 

Thanks guys. Does anybody have a parts list from a 2009 20 hp? Even if you have a serial number I can order a parts list for that engine. I have the manual and parts list ordered for my engine. The boat is pretty decent, but who doesn't want a faster boat? I am also having carb issues where it will bog hard and require me to keep goosing it, or pumping the prime, and have the choke out to keep running. I think there is some junk in the carb so a new carb with 5 extra hp would be the perfect solution!

 

I just got the part list, and guess what, its the same for the 15 and 20. Here are the only differences between the 2. They have the hp rating in bold when they are different and I went through the entire parts list. The heads, crank, and camshaft are the exact same.

Code:

PN: 3303-853720T14 carb assembly 15 hp tiller
PN: 3303-853720T15 carb assembly 15 hp remote
PN: 3303-853720T16 carb assembly 20 hp tiller
PN: 3303-853720T17 carb assembly 20 hp remote
* I'm not sure if these part numbers include everything in the carb.

PN: 803689008 15 HP JET, pilot (#46)
PN: 803689009 20 HP JET, Pilot (#52)

PN: 19-802702002 15 hp plug
PN: 19-802702001 20 hp plug

PN: 812650021 Main Nozzle 15hp tiller
PN: 812650019 Main Nozzle 15hp remote
PN: 812650022 Main Nozzle 20hp tiller
PN: 812650020 Main Nozzle 20hp remote

PN: 802701011 Jet Main #121 20hp
PN: 802701010 Jet Main #99 15hp
* It looks like you may need the carburetor assembly for the 20hp to fit the above parts into, but I can't tell from the drawings.  It might just be an either or type of thing

PN: 48-897750A10 15hp propeller (9.25" x 9 pitch)
PN: 48-897752A10 20hp propeller (9.25 x 10 pitch)

This is for a 2009 4 stroke model, but there are a bunch of serial numbers listed. I think my plan will be to buy the prop, nozzle, plug, and jets and see if they fit in the same carb body. Fingers crossed! (I probably won't get to this project for a while due to my long project list, but its gonna happen!)

 

Timing, jets and throttle limiter . . . The carb rebuild kit has both sets of jets, so give a it a few more degrees of timing, swap out the jets and knock off the limiter cap or screw. Also check the specs. what RPM does it produce 15 HP, ditto the 20 HP. I'm pretty sure you'll find the 20 HP is permitted to twist up higher (no limiter).

 

15 to a 20hp

Well I just just installed the new jets and nozzle for a 20hp in to a 15hp carb and every thing fit!! so the carb bodies are the same......Also installed on a new prop!!

Have not started it yet as we have about 10" of ice....going to have to wait till spring!!

 

The carb bore could still be larger and it must be to get a 30% power increase if everything else is the same.
If they dont sell the throttle butterfly as a part you have no way to compare them without having both in your hand.

 

Yep, see if the carb butterfly is the same part number between the two models. I suspect it is the same and they just choked up a 20 HP with RPM limits and smaller orifices to get a 15.

 

check the reed plate too....sometimes it has a blocked off reed orifice to restrict the air flow.

 

before going thru the expense of motor conversion, check height of motor on boat make sure motor is mounted at proper height. I have a 450 lb smoker craft 14 ft. I raised motor 1.5 inches i was motoring along with 2 people in boat at 12 to 13 mph i am now at 18 mph, make sure tall tail is working properly and motor rpm sounds right you will know,amazing what 2x2 will do, but be carful. cavation plate sould be level to bottom of boat.

 

The underside of the cav plate could be 20 mm above the bottom of the boat as a starting point not flush !! what is the motor hp ? a 14 foot with a couple of people sinks down so setting the motor up is not a problem !! cut down on spray from the front of the leg at speed also makes the steer lighter . also check the motor is vertical and in the middle , you would be amazed at the number of boats where motors are not in the middle and are cockeyed not straight !.

 

motor is a 15 hp 4 stroke mercury . My cavatation plate was 1.5 inches below boat bottom its a different boat now. i hav no spray i messed with the tilt rod and a gps onboard wow its great it does not jump on plane right away, I figure i am moving close to a 850 to 950 lbs with mom ,picknick lunch 50 lb dog ,chairs cooler, rods towels, and misc items,mom sits in front of boat,period. gas milage has increased much. our trip to our fishing hole is 14 miles round trip, 3 gal tank was close to half a tank now its a little better than a quarter. adjusting the motor height is a good thing. I took 3 pieces of wood with me ,1 1/4, inch,1 inch, and i started with 1 1/2 inch .1 1/2 inch worked best.hope this helps. there web sites that tell how to set motor height. boat load is key factor. the 15 hp in all reality is to small for my boat. max hp on the boat is 40 hp 2 stroke. I would be afraid to set a 40hp 4 cycle on her it would sink her, to much weight.