re-powering...i put it in the wrong the first time

[uni_panther]

i have a 16ft jon boat extra wide and already have a 20hp johnson. i've added plywood floors with carpet and 3 seats and the my current motor pushed it just fine last summer but with the new additions not sure how well it will get up to plane. i am looking at buyin a 33hp johnson for a good price and was wondering if this would b a good idea. my boat is rated at 30hp so 33 is just a smidgen over what its rated for. i guess my question is is that will the 33hp b too much power like scary fast with a flat bottom being how its rite at the max rating? and another concern is weight. would the motor weigh that much more being im kinda concerned about the weight issues with all the gear etc. in the boat now?(890lbs max) the motor seems like a good deal to pass up. the two motors are the same year being 66's and didn't know if they really weighed much more than each other...any advice would b greatful. thanks if any input.

 

[cr2k]

Re: re-powering...i put it in the wrong the first time

I can't see where that would make much difference. I mean HP ratings on outboards are just a numbers game like the muscle cars of the late 60's early 70's. An outboard rated at 9.9 usually puts out 10 12 hp and is rated 9.9 because lots of lakes won't allow anything 10 hp or over.

A lot of 9.9s and 15s are basically the same engine with maybe a different head (compression ratio) or a slightly bigger carb or maybe just timing.

33 hp sounds like an old speed twin or sport twin or that kind of engine.

surly 3 hp would barley make up for the weight of the new floor and carpet.

In the 70's we would take a 16 ft ski boat rated for 90 hp, put an aluminum plate on the transom and drop on a 150.

Having had a john boat, I can't see why anyone would want one. To me it seemed tippier than a canoe.

But I would not worry about 3 hp. 15 maybe but not 3.
Good luck with your project!

 

[reelfishin]

Re: re-powering...i put it in the wrong the first time

Sounds like a nice boat.
My concern with the 33hp wouldn't be the added 3 hp over the max rating so much as the added weight. The 33hp if I'm thinking of the same motor, is an older motor which was based on the old Big Twins, which means it shares it's basic design with a 40hp not a 30hp.
The added weight would most likely not be overcome by the added HP either since the transom would no doubt sit much lower and more power would be needed to get up on plane.
Your best bet would be to find a newer 25 or 30hp motor which would be much lighter and give you a far better result. The earlier 25hp Johnson/Evinrudes with the pin drive props were the best sleepers of the bunch as they were a bit lighter than the newer versions.

I have a 1967 33HP Evinrude which I had on a 14' fiberglass MFG, which did well on that hull, but it was heavy, that same boat did much better with a newer and lighter 35hp Johnson.

I also used to have a 16' Big Jon with a 15hp motor that did just fine with two big guys. That boat had wood decks, three seats and one pedestal, bow mount trolling motor, plus a livewell and two batteries. It ran along at about 19 mph on plane.

Your 20hp should do fine although a prop change may be in order.

 

[uni_panther]

Re: re-powering...i put it in the wrong the first time

thanx for the help. i wasnt really too worried bout the 3hp over rating but it was in the back of me head this whole time. the other thing was to maybe change the prop. what would you guys recommend as far as pitch and whatnot and where would i find one to purchase?

 

[uni_panther]

Re: re-powering...i put it in the wrong the first time

i forgot to ask too...would getting a new carb to put on my 20hp, like off of a 25hp or 30hp beef it up a little or is that opening up a new can of worms by having to change a whole lot of things besides the carb. ive used the 20 last summer and tore it all apart and put a pretty penny into it replacing seals and giving it a once over and new paint and decals. u never know whats on the inside ya know. i will pry just stick with the 20hp but what can i do to squeeze all the power out of this guy?

 

[steelespike]

Re: re-powering...i put it in the wrong the first time

What year is the 20?Be sure it is in excellent tune,throttle opening all the way.
prop in excellent condition.
Start by checking your setup.Antivent plate just above the prop should be about even with the bottom or slightly above.If its the old style 2 piece gearcase you may not be able to raise it as much.
The best way to get her setup is to get a tiny tach(reasonable and easy to install.
One for your motor would fit any 2 cyl. 2 stroke, cost about $40.Also beg or borrow a gps.Test the boat, get us the prop size ,on hub or under the prop nut, and your max rpm and speed.The motor needs to operate within its designed rpm range to be efficient and stay healthy.

 

[uni_panther]

Re: re-powering...i put it in the wrong the first time

its a 66 fdl-20c. i just tuned it up and had to take the power head off, with some help, to fix the couple of bolts that hold it to the pivot tube and i dont know if its just too cold out being in the low teens here in iowa or if we missed something but its damn hard to twist the throttle handle to get it to fully open up. it opens up fine up to a certain point but to get that guy all the way over to fast its a pain. it worked great last summer. need some lube somewhere or just the cold messing with my head? and im sorry i dont know what this antivent plate is guessing near the prop and slightly above what. sorry im a goon and learning as i go.