Not sure how high this engine should be mounted in jackplate and what prop pitch will work best. Right now engine is all the way to the top of jackplate with a tempest 25p. Any help would be appreciated. When I hit around 55mph gives me a low pressure alarm need to reduce throttle. Has side pickups on lower unit and four holes on the front of the cone pickup
Last edited by Tylerk; 07-29-2022 at 03:53 PM.
TylerkOriginally Posted by Tylerk
Based on the title, are you saying that this engine is a '03 Merc 300X EFI Pro Max? and is on a 21' 2003 Triton TR21? which in its worst conditions would push that boat well behind 55 mph.
Do you know what your current P2P is? What size JP? I would suggest you start at 3.5" P2P with a fresh prop, since I believe that a 25" pitch may not be enough. I spin a 26" on a 2003 Merc 225 EFI off a 10" JP set at 2 7/8"
What was your water pressure when the alarm went off?
When was the last time this engine was fully tuned? including water impeller and compression check?
What load did you have in the boat?
Yes its a 300x on a 2003 tr21. Engine is set as high as it can go on jp. Ordered a new impeller kit just in case. Not 100 % sure on p2p. Can tell you from the lower bottom on boat to the plate above the prop is around 4 inches. Not sure how to post a pic here
Close to a full tank of fuel 4 lead batteries, empty livewell 2 guys (400lbs) not a ton of gear trolling motor.
Tylerk
I will attach a picture on how to measure for P2P. Make sure your keel is level with the ground and follow the steps.
iUz1m7.jpg
When you do your base line numbers, I would suggest you do it by yourself with half tank, which is how most company do their testing.
When was the last time this engine was fully tuned? including water impeller and compression check?
I will get a good measurement tomorrow and post my results.
I am not sure last time impeller was done. I ordered a new kit from mercury should be in this week so will get the impeller kit installed right away. Tune up was done last fall when winterized according to previous owner. Showed me the bill for winterize and spark plugs and compression test which the shop just marked as okay.
If the motor is running with this much lack of power, I would do a proper leak down and compression check, since to me it seems as if not running on all cylinders.
There is a proper way of doing compression test, and if not done correctly, you will get incorrect readings.
Any shop that does a compression test will normally put down the actual numbers on each cylinder and they should all be within 5+- psi of each other.
Are you thinking your down on power? or you just cant get there due to low water pressure?
Because ive been through all this in the last couple of months I can tell you.
First: go ahead and change the Water pump. That gets that out of the way. and make sure all openings are not clogged while you have the lower off.
Second: if it has the compressor strainer that needs cleaned.
Third: make sure you start at the Correct Prop to pad Start at 3 1/2"
Fourth: Maybe (should be first) If you dont have a water pressure gauge you need one. If you do, as your trimming up, watch the gauge to see when you start losing pressure. Find out what the minimum wide open throttle pressure is for your engine.
If you see it dropping dont trim any more .
I dont know for sure But Im betting your too high on that jack plate.
And for sure check compression and make sure your hitting on all cylinders.
As an example . when I bought my boat a few months ago I checked compression and test ran it. compression was good and it ran fine but to me it seemed like it should run faster. thinking it was a prop problem I paid for it and took it home.
Then I figured out it wasn't firing on #4 . Thats another story and I fixed it but the engine can run good and not be hitting on all of em.
Check your prop to pad and set the motor at 2.5 inches under any lower and you won't be able to control the chine walk at speeds over 60. With a 300 hp motor that boat will run over 80 mph and if you have never ran a fast boat you need to find someone to show you how to drive it. I have a 2004 with a 225 efi and it will run close to 80 with a 27" prop. I'd look for a 27" tempest for that motor and put a complete water pump kit in it not just an impeller.
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