Evinrude 9.5hp to 15hp quality conversion

[alumistar]

I have a 1965 Sportwin 9.5 on a 12ft. Starcraft Superstar. It almost gets on plane but not quite. I have heard a few different suggestions, but I am afraid of what may happen if I do it wrong. Can you help?

 

[Dhadley]

Re: Evinrude 9.5hp to 15hp quality conversion

You might look at the set up you have now to make sure youre getting the most out of what you have already. There wasnt a 15 thats built from the 9.5 and the 18 is a completely different motor. Look at the cavitation plate and make sure its not running too deep. Try to get it about level with the bottom. <br /><br />Good luck!

 

[alumistar]

Re: Evinrude 9.5hp to 15hp quality conversion

cavitation plate is exactly 1" below the bottom of the transom. I have a tinytach ordered, but I know I'm only pulling about 3500rpm( Therein lays the problem) motor runs strong, but I live and fish above 5000ft. So I'm trying to beat mother nature in that sense. If there is nothing that I can do what's the biggest I should go, with respect to the 70lbs. that my 9.5 weighs?

 

[Paul Moir]

Re: Evinrude 9.5hp to 15hp quality conversion

Your not running too deep then.<br />Sounds like your running on one cylinder. Remove one spark plug lead and try it out to determine which one isn't pulling it's weight.<br />The most common cause for that engine is a cracked ignition coil. That happens to old ones from that time. They arc over at high rpm causing one cylinder to missfire.<br /><br />Good luck!

 

[Chinewalker]

Re: Evinrude 9.5hp to 15hp quality conversion

If you know you're spinning 3500 now, then you are probably running on both cylinders. It sounds to me like you've got a tuning problem or a tired motor. Have you checked compression? Are you getting full advance on the throttle linkage? It's also possible that you have the wrong prop, or your prop might be bent or damaged? That 9.5 on a light 12-footer ought to scoot, regardless of the altitude...<br />- Scott

 

[ledgefinder]

Re: Evinrude 9.5hp to 15hp quality conversion

Try pulling the starter cord slowly a few times, with the kill button pressed. Does the resistance going over feel the same on both cylinders, or can you repeatably tell one cylinder from the other? If they're the same, you're cylinders are likely OK - it's rare for them to be able to wear down at the same rate. If one turns through top dead center with little resistance, then that's at least part of your problem. <br /><br />However, even a leaky cylinder produces pretty decent power, so sounds like it may have other problems. Does it seem to run smoothly? Did this problem just occur, or has it slowly built over time. <br /><br />The 9.5 is a great motor, but is basically a hopped-up 7.5. The 9.9 looks the same, but is basically the 15 with a smaller carb (and in some years other tuning changes). Thus the 9.9/15s are a good deal stronger than the 9.5, but also heavier. A good running & well-propped 9.5 ought to be plenty of motor for a 12-footer.

 

[knobby]

Re: Evinrude 9.5hp to 15hp quality conversion

here's the scoop on the conversion + maintenance<br /> http://www.pugetsoundanglers.org/Fishing Info/Johnson 9.9_15.htm

 

[wayne h]

Re: Evinrude 9.5hp to 15hp quality conversion

i have a 9.5 and had the same problem make sure your linkage is timed right and the arm that throttles the carb is not warn. you will be surprized that alittle wear on that finger will drop your RPM's<br />there is a line on the plate under the flywheel that when the finger is on that line it should be touching the throttle linkage on the carb. if its not you have to losten the screw that is in the center of the carb linkage and push it so that the plate (with the line) cam follower and the throttle all touch.<br />take a look and see if that is setup right and let us know. <br />is thats right maybe your not running the right size prop i have about 2-3 diffrent size props i had to play with also to get my RPMs up.<br />there are great motors when they run right.look for a factory shop manual on ebay they are on there pretty cheap and are deffrently worth having.<br />i hope this helps you.like people have said there is no real hope up for the 9.5 since its a hoped up 7.5 already and to go with a 15 hp you will be gaining weight you dont want on a 12 footer

 

[alumistar]

Re: Evinrude 9.5hp to 15hp quality conversion

o.k., so i have a 8 1/4 x 8 1/2, a 8 x 8 1/4 and an 8x7. They two smaller props I have not tried yet due to the recent chill the hit us. If my problem is not motor, which it sounds like it isn't,(95/93 compression, good spark, good throttle response) then it must be the prop, right? My props will make the motor spin faster, but will it give me the thrust I apparently need? If not, would anyone recommend a 15hp, or is that too much motor?<br /><br />p.s. thanks too all for the advice given!

 

[Solittle]

Re: Evinrude 9.5hp to 15hp quality conversion

A 15 would give you the performance you are looking for. I have a 9.9 on a 12' that runs just fine and gets the wife & I up on a plane & we ain't small people.

 

[alumistar]

Re: Evinrude 9.5hp to 15hp quality conversion

as long as it is agreed that a 15 isn't too much motor for a 12ft alumi. then that is the route i will follow i guess. if anyone has any other ideas on this i would love to hear them. thanks all for your assistance!!

 

[Paul Moir]

Re: Evinrude 9.5hp to 15hp quality conversion

I would expect your 9.5 would plane off a 12' boat with just about any prop. That is unless there's something you havent told us about the boat, like it weighs 2000 lbs, or there's something wrong with the engine. Since it's not compression, it's probably not an expensive fix.<br />When I posted, I was assuming your 3500 rpm figure was probably optimistic, and you were running at half power (~2500 rpm). That would probably bring your boat almost to plane. The obvious reason for such a loss would be running on one cylinder. Do follow all the good advice givin above! <br /><br />PS - Legfinder and Wayne describe the 9.5 as a hopped up 7.5. I have to admit, i don't see the similairity. It seems to me the block is vastly different (it's reeds and carb are in a completely different place), as well as the bore and stroke. The 9.5 has roller bearings, and a thermostat too. I'm not looking for a debate, but I would like to know why it's supposed to look like a 7.5.

 

[alumistar]

Re: Evinrude 9.5hp to 15hp quality conversion

I guess i'm not completely sure what the rpm is. i ordered a tinytach today and i expect it in the next couple weeks. hopefully it will give me the difinitive answer that i need to solve the rpm question. as far as i can tell there is good compression in both cylinders (95/93)psi. both plugs spark. i do know that altitude plays badly with a motor. if i am only pulling 2500 or so, then a prop change is definitely needed, whether it is the answer or not is another question. i am skeptical on the thrust output of a smaller prop as i have been told by many different boat dealers and repair shops very different answers on what rpm you gain from the size reduction in the prop, and whether or not that rpm gain is motor gain or prop gain. if i got that figured out it wouldn't matter whether it was the motor or the prop rpm since i know my gear ratio(13:23). i guess what i need to know is the absolute holy grail answer on:<br /><br />RPM vs. THRUST and, 9.5hp vs. 15hp and,<br />how big of a motor should one go on an aluminum <br />1972 Starcraft Superstar that carries 600lbs. including motor(70lbs),some 30 lbs. of fishing gear, my fat butt(270 lbs), my 3year old(38 lbs), and, on occasion, my girlfriend(135 lbs)-p.s. don't tell her i said anything about her weight! <br /><br />"It's not what you have, it's what you do with what you have!"<br /> boating is fun huh?