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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 16217
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I have has a 2015 mercruiser 3.0 TKS repower installed in my

Customer Question

I have has a 2015 mercruiser 3.0 TKS repower installed in my 17' bow rider with a alpha one gen 1 (1990) leg. I bought the repower because I froze/cracked the previous engine which was running well. Reasonable pull (for an I/O) in getting wakeboarders etc out of the water. It had about 700 hrs on it.
I was previously running a 19P prop on it. After taking the new installation out the power to plane is very very sluggish. Seems way less than a prop step. I have stayed mostly in line with break-in recommendations but did run WOT on reasonably calm water (not glass) to see what max RPM was. I was only getting about 3800. I can say for sure the WOT RPM prior to this installation.
I understand I need to be in the 4400-4800 RPM. Does this mean I need to drop my pitch down to 15-17P?
Could it be something other than propeller pitch? The engine sounds fine - like the previous engine. Runs fairly smooth. It started out idling fine but after a bit it starting idling with very low RPMs so I increased the idle throttle limiter screw to give it a bit more gas - which helped.
Do you think it is the prop? Should I be looking beyond that?
Submitted: 2 years ago.
Category: Boat
Expert:  Jason replied 2 years ago.
Hello my name is ***** ***** am I speaking with?
A prop pitch change isn't going to fix a lack of 1000 rpms (get you from 3800 to 4800)
How old is the fuel? Do you have another fuel tank you can run the engine off of, like a portable outboard style tank?
Customer: replied 2 years ago.
I don't have an outboard style take that I can use.
I didn't drain the tank so there would be some old gas in there - fairly small amount in the tank. I did add about 45L of premium gas to it...
Customer: replied 2 years ago.
I didn't answer your first question: I'm Mike.
Expert:  Jason replied 2 years ago.
Hi Mike. Old gas and fuel starvation would both cause the same issue. Wether you have to borrow one or buy one, you want to run the engine off of a portable tank filled with brand new gas. That would rule in or out both scenarios. If it runs better on the portable tank, then you know either the gas in the tank is no good. Or, there is some kind of blockage or air leak and you are not getting enough fuel to the engine at high rpm. Does that make sense?
Customer: replied 2 years ago.
Would this also answer why I needed to adjust the idle throttle limiter?
Expert:  Jason replied 2 years ago.
What exactly are you calling a throttle limiter?
Customer: replied 2 years ago.
At the carburetor, where the throttle cable attaches, there is a screw that seems to limit how much the throttle backs off when pulled back to neutral. I rotated this one turn to keep the RPM higher when in neutral. This wasn't needed at first but was needed after an hour of running or so.
Expert:  Jason replied 2 years ago.
Ahh You are talking about the idle speed screw. No that would not have anything to do with it, that only controls idle speed. Run the engine off another tanks and see what happens. There are other ways to check for a fuel restriction, but that does take pressure and vacuum gauges. Running it off another tank is easiest way to get you pointed in the correct direction. Does that make sense? Also, I know you said this was a new engine. Has compression and spark advance been double checked.... just to make sure?
Expert:  Jason replied 2 years ago.
Is running on a portable tank something you can do today and get back to me on?
Customer: replied 2 years ago.
Thanks re idle speed. I guess what I was asking was whether my need to increase idle speed could be because of bad gas or blockage and thus need to increase the amount of gas going portable tank - I'm not on the water today but will try to get things setup for trying a portable tank on Saturday.
Expert:  Jason replied 2 years ago.
Gotcha. Bad gas would do it. 3.0 liters don't come equipped with fuel water separating filters either stock. So if there is any water in the fuel, it will make it's way into the carb. Will it idle at say 650-700 rpms when in gear?