90 HP Johnson Outboard

[Kalino]

I just purchased a new boat/motor Seaswirl/Johnson...however I'm questioning the motor installation measurements..??<br />The dealer says it's according to spec...however according to the owners manual it's not. How important is the position of the motor anti-ventilation plate with reference to the boat bottom. Spec says parallel with the bottom...and no lower than 2 inches below. Can anyone help me...!! At the present the top of the prop is level with the boat bottom...is this okay..!!

 

[Dhadley]

Re: 90 HP Johnson Outboard

Correct X dimension height is a combination of hull design, type and style propeller, setback, balance and gearcase shape. I can't imagine a situation where the anti-ventilation plate should ever be below the keel. matter of fact if it is there may be a spray of water up the mid section that can result in water injestion. <br /><br />As a rule of thumb (one of several) remember -- a stainless prop, like an SST II will run higher than an aluminum, a Raker higher and a Stiletto higher yet. A 4 blade will run higher than a 3 blade. <br /><br />The most important thing is proper RPM with an average load. If you tell us what your specs are we can calculate slip factors for your current set-up. What top RPM (average load), water pressure, accurate speed, style of prop, size of prop and type of fuel.<br /><br />Good luck!

 

[Kalino]

Re: 90 HP Johnson Outboard

Dhadley<br />Thanks for your quick reply....however I'm still trying to track down more info you requested to answer my motor installation query. The only thing I know is 90HP@5000 RPM, the prop is 3 blade (AL) with a diameter of 12-3/4 inches, I'm guessing at the pitch here of 21". I've nothing on water pressure...On monday I'll call OMC and see if they have the latter. The motor installation instruction is missing from my package....The dealer's tech says the motor is set up okay....???? I disagree with him.<br />Thanks again pal for your outboard savey.<br />Regards<br />Norm

 

[Dhadley]

Re: 90 HP Johnson Outboard

Get a water pressure gauge. This will tell you Before something goes wrong and how high you can mount the motor. If top capeable RPM is only 5000 the motor wont last long. The motor should be capeable of 5800 RPM with an average load using FRESH 87 octane, good oil and Champion plugs. Try raising the motor before you change props.<br /><br />Good luck!

 

[Dunk]

Re: 90 HP Johnson Outboard

It would help to know what kind of boat you are talking about. It also sounds like you haven't had it in the water yet. If she's propped with a 21" pitch prop it must be a small light boat. Lots of lighter boats will run the tips of the blades out of the water and hang on great. Meaning they don't ventilate(cavitate). I'd at least try running the boat before you start second guessing the dealer. Especially if the dealer sells this kind of boat. They usually know where to hang the engine especially if it's up a couple bolt holes on the mount bracket. Dealers that don't care just bolt them up flat down on the transom.<br /><br /> I disagree with Hadley on the 5800rpm's. Those 90's are rated from 4500 to 5500 and the 90 puts out her best power at 52-5300. When you twist them higher the 90's having smaller carbs and jets than the 115hp will go into a lean condition when you get over 5500 on them. The 115's you can run to 5800, but I wouldn't do it with a 90hp.

 

[Dhadley]

Re: 90 HP Johnson Outboard

I've never experienced a lean condition with any of my V4 crossflows due to RPM. As a matter of fact I have an 88SPL that's capeable of 6000 RPM with an average load and it's been running fine for the last 5 or 6 years. We have found that motors set up at 5200 to 5300 at WOT tend to coke up quicker plus the holeshot isn't as good.<br /><br />Good luck!

 

[Kalino]

Re: 90 HP Johnson Outboard

Dhadley/Dunk<br />Bombardier/OMC says proper height for my set-up should be 1" above keel, with zero setback on the motor mount.

 

[Dhadley]

Re: 90 HP Johnson Outboard

Sounds like thats a good place to start. Especialy if they were talking about an aluminum prop. Start there and dial it in according to your prop. Let us know how you make out. <br /><br />Good luck!

 

[Kalino]

Re: 90 HP Johnson Outboard

Hopefully I'll have most of my boat defeciencies corrected by week ending....I'll make reference measures prior to testing...then adjust back-set and height to obtain maximum performance...Bombardier is very interested in what I've arrived at when completed. Maybe a trip to Montreal is in order to visit OMC's new owners. <br />Regards

 

[Dunk]

Re: 90 HP Johnson Outboard

Hadley, I can garranty you don't have many hours on that engine at 6000. She may turn up that high but she won't live long like that. Either that or your tach is wrong. V4's set a harmonic vibration right around 6-6200 that will destroy the crank and bearings. The power drops off considerably once you cross the 55-5600 rpm in any OMC V4 and before that in the 88/90hp. I would recommend at least 2" more pitch in prop.<br /><br /> Engine height is a relative term. It all depends on the dia of the prop and the weight you are trying to push with it. The more weight the deeper it will need to run. Look at the high speed bass boats. They'll hook up and twist a wheel with the prop shaft above the bottom of the boat. This is because the hp/ratio is extremely high and they only need 1/2 the prop in the water. After that you get into custom props made to be running in a surfacing type operation. That alum prop is at the low end of the performance range and will need to run deeper than a decent SS wheel like a Stiletto. <br /><br /> If this boat and engine are new you've got 10-15hrs of breakin to do before you start dropping the hammer to test props and engine height.

 

[Kalino]

Re: 90 HP Johnson Outboard

Dunk/Dhadley<br />Thanks for all your info/replies with respect to what I thought was an simple question with a simple answer. Talk about learning something everyday. I'll tell you one thing...most of my questions (with your help) to the dealer came with a reply of...we'll get back to you on that one...

to which they have no idea what I'm talking about. I'm very surprised at the lack of knowledge at most boat dealers/repair shops...and I'm only comparing that to me....and I'm starting at zero experience with boats. Once again I'm glad I found this site with all the wonderful people to share information on our passion for boats.<br />Regards to All<br />Norm