How to set the engine height on an Outboard Jet Engine

One of the essential processes of getting a jet boat right is to get the outboard mounted at the correct height.  I can’t stress enough that the mounting height of an outboard jet is CRITICAL!  Unlike a propeller driven outboard there isn’t a much room for error here and getting right the first time is typically impossible. 

The pump must receive water during the entire planing process or it will ingest air and create cavitation which can lead to  engine damage (specifically the impeller) and poor boat performance.

The target height is for the front grate pin on the intake to be level with the bottom of the boat when the engine is mounted and trimmed all the way in.

The best way to check engine height is to use some type of straight edge such as a level or yard stick.  

Step one is to trim the motor in or down entirely.  On outboards without power trim you may have to manipulate trim pins or bolts that the engine rests on.  You must set these pins in the lowest holes as close to the transom as possible.  For outboards with power trim it is easy, just trim down as far as possible.  You still need to examine the stop location to confirm there are no other adjustments necessary to trim down further.  Some power trim models use bolts to limit the trim arc.  

Step two is to verify the front pin of the intake is level with the bottom of the hull.  On the outboard jet intake there are two pins that hold in the grates.  The forward or front pin closest to the forward side of the engine closest to the boat is the indicator you’ll use when setting the height.

Place a straight edge on the bottom of the hull projecting to the rear away from the transom.  If the boat is a tunnel hull the straight edge should be in the top center of the tunnel.

This straight edge should intersect exactly across the front intake grate pin.  If it does not then the engine will need to be adjusted until this alignment is correct.

Adjusting the Outboard Jet Height

You may already have holes in your transom for an outboard engine.  Assuming they were drilled accurately in the center of the transom then this is a great starting point.  

Jack Plates

Ideally, you will not want to have ANY form of jack plate or devices between the outboard and the transom.  The further the outboard jet sits away from the transom the more potential for air to enter the pump.  However, one of the necessary evils is that you have to raise an Outboard Jet around five inches or so to retrofit a prop boat and this is usually accomplished with some type of riser.  It’s okay this isn’t a make-or-break requirement but the best practice would be to reduce or eliminate any type of riser plate.

When selecting a jack plate try to find a riser only.  These are fixed aluminum plates that bolt to the transom with no adjustment.  Jack plates typically have some form of adjustment and a measurable setback try to avoid any of these plates.  However if you do have one then there is a good chance it can be modified to a fixed style riser.

Trim the engine all the way into the transom.

Use a straight edge on the lowest portion in the center of the hull as a point of reference.

Line the front pin of the jet foot intake with a straight edge.

Height Adjustment Trick (Extra Transom Holes)

Now here is the trick on tweaking the height of an Outboard Jet to get it just right. Its an old school method of adjusting engine height and works great. Its a little confusing but once you get passed the ah ha moment then you can see the elegance in this solution.

If you have existing holes and moving the outboard up and down a hole doesn’t seem to get the height adjust exactly right. There are many but this is a best practice and works fabulously.   

If the bottom mounting holes on your Outboard bracket are slotted then you will need to drill another set of  top mounting holes in your riser.  If your outboard uses bolt holes on the bottom and top of the mounting bracket then you’ll have to drill two new bottom holes and top holes.

The trick is to drill the new set of holes at 5/16 of an inch above the existing top holes. This will give you 11/16 from center to center between the existing top holes and the new holes. The reason for this is the standard outboard mounting bracket holes are 3/4 of an inch from center to center, so you are able to move the engine up 3/4 inch but what if that is too far and you need to be just a hair lower or higher?  By adding holes 5/16 of an inch higher you can alternate between top holes to dial in the height. Using the top holes then then bottom holes. Then going back to the top holes as you “walk” the engine up or down to set the height.

There are minor tweaks to these suggestions for special scenarios but these are best practices and will get your jet set up for great operation.

You can also find helpful tips for Outboard Jet installation here on Outboard Jets website.