no hi speed on 3hp Johnson with inflatable

[mrdh]

When I try my 3hp in a bucket on shore it works perfectly. However when I put it on my inflatable boat (12ft Sevelor) it does not achive the high speed. Some posible reaseons I figure maby the motor is off tilt, perhaps it is mounted to low. Would either of these situations result in fine performance on low speeds but not be able to exelerate? any suggestions would be helpfull mrdh@rogers.com

 

[Drowned Rat]

Re: no hi speed on 3hp Johnson with inflatable

Hi LP. The motor should be as level as possible, but as long as it's close you should be fine. The idle relief ports on the exhaust leg should be above the water line when mounting the engine. As long as they are, it should run the same as in the bucket. What happens when you try to accelerate? Post your exact problem and you'll get some answers.

 

[Reel Appeal]

Re: no hi speed on 3hp Johnson with inflatable

If the cavitation plate is more than a couple inches past the bottom of the boat it is mounted too low(prop too deep),increasing drag.Inflatables have small transom heights which contribute to what your describing.

 

[mrdh]

Re: no hi speed on 3hp Johnson with inflatable

Thanks for your comments. For the most part the motor is level and while a bit too low, the exaust ports are exposed. The problem more specifically is not a thrusting issue but with the fact that the engin itself does not spin faster (it doesn't sound any louder past the mediume speed) but this only ocurs when it's on the boat - leeding me to belive it is an issue with the way I mounted it. Can you think of anything that might cause a motor not to accelerate because of its installation?<br /><br />Thanks again.

 

[cobra 3.0]

Re: no hi speed on 3hp Johnson with inflatable

Is your "lean" knob properly adjusted...assuming you have one? Is the choke working properly (open all the way). Is the carb clean?

 

[mrdh]

Re: no hi speed on 3hp Johnson with inflatable

Thanx Cobra. It may very well be either the choke or the lean... but then why would it work in a bucket and not on the boat - that's what's baffaling me... it works perfect in a bucket, and doesn't go in high speed on the inflatable boat.<br />thanx

 

[voodoo]

Re: no hi speed on 3hp Johnson with inflatable

in the bucket it's cavitating or the water is circulating allowing it to get to the max hp rev range<br />I cannot see 3hp pushing a 12 foot inflatable any faster than a few mph. Inflatables have big drag.<br />Your prop is hooking up but your motor aint got the guts, go down a few inches in pitch may get you a little more speed but don't expect to get on plane.

 

[mrdh]

Re: no hi speed on 3hp Johnson with inflatable

Thanx Voodoo, just so I understand you, the motor won't spin faster because there is not sufficient water circulating around the lower unit? And this is because at lower speeds there is too much drag and this prevents the motor from being able to accelerate. My boat is rated for a 2.5 hp any more hp and it would flip (this is what I was told by the mfr.) So how could this be if the boat would create too much drag to even achive suffichient speed to flip it. Am I missing something?<br /><br />Thanks again.<br />dh

 

[voodoo]

Re: no hi speed on 3hp Johnson with inflatable

..in the bucket there is alot of turbulance so the prop will spin quickly as it is doing very little "work". look at it this way, if your car is on ice and you floor it you will hear the engine rev and the tires spin at 100+ mph (because the car is not really moving the only "work" being performed is the spinning of the tires and the little bit of friction) now take that car, give it lots of traction, make it move the car and try to do the 100+. You are now performing work and require lots of power.<br />I