Water pressure problems on trim

[Fastrike175]

I have a 1991 Ranger 481V with a 1992 Johnson Fastrike 175. The problem I am having is when running wot it normally shows 21psi on the pressure guage. I can trim the motor to almost where I need to be and pressure stays steady. To get optimal speed I need to trim it just a little more. When I trim it to perfect position pressure drops from 21 to 14. Is this being caused by the water intake holes sucking air? A friend of mine told me to tape off the top two holes and see what happens. Just was wondering if anyone had any suggestions.
(Also just to help I am running a jack plate and have dropped the motor quite a bit from were i received it and it helped some but didn't cure problem. Also motor is proped right because at wot it is turning about 5500 rpm. Getting about 54 mph now and if I could raise bow a little more could run maybe 60+ mph.)

 

[HighTrim]

Re: Water pressure problems on trim

Welcome to iboats Faststrike.

Wow, where is Dhadley when you need him

I would want a bit more RPM out of her, so maybe getting to 58 or 5900 would keep the trim at a level so as to still get proper pressure readings.

I would not run it with only 14 psi.

If you are patient, Im sure more educated readers will see your post and give you a more definitive answer. As stated, Dhadley is definately one of the guys you will want setup/jackplate advice from.

 

[Chris1956]

Re: Water pressure problems on trim

Fast - Why not have someone look at the lowerunit and see if the water level is down a couple of inches below the AV plate?

Additionally, if just the top waterintake hole is exposed to the air, you can plug it and elongate the lowest hole a bit.

 

[Fastrike175]

Re: Water pressure problems on trim

The problem is when I get the motor to where it should be for fastest speed and best ride it is 6000RPM. But with the water pressure dropping to 14 or 15 I don't leave it there but for about 3 seconds then right back down and water pressure returns to about 23psi. Boat starts to accelerate good but don't leave it there long enough to see what top speed would be. And your not talking but about one or two small bumps down. It just seems to me im sucking in air and loosing my water pressure. I am running a stainless raker cupped prop 14.5 x 24. I only have about a 1/4 inch more to go down on my jackplate. Boat runs strong but just lacks a little to get it were bow is high enough to run on pad only.

 

[Fastrike175]

Re: Water pressure problems on trim

Has anyone got any suggestions?

 

[emdsapmgr]

Re: Water pressure problems on trim

From your description, you are probably exposing the top two holes of the water intake holes, causing the lower pressure. This is a fairly normal problem with jack plates and high-rake props with a lot of bite. You run out of water pressure before the prop loses it's bite. There is some discussion regarding just how low can you run the pressure and not cook the powerhead. Some will say 10 lbs, others will say no less than 15. One potential solution. Fill in the top two holes of the water intake. (see attached picture) There is still adequate water volume and pressure intake to run the engine. You may find that this solves your problem.

 

[R.Johnson]

Re: Water pressure problems on trim

Besides the pressure, my concern would be sending aerated water to the power head, that would not cool as well.Sudden loss of prime to the pump may also be a concern. Closing the top intake hole's, and monitoring the effect sounds like a good way to go.

 

[Fastrike175]

Re: Water pressure problems on trim

That is what a friend told me to do I just wanted to see if anyone has heard of doing that. Thanks, I'll first try just the top hole then if still loosing pressure the second. I know from experience that it will not run safely at 14psi.