2016 4.5L mercruiser i/o Very weak performance

[sheltonoil]

Just bought 2016 Hurricane Deck boat SS201. This 250hp engine is weaker out of the hole and planing off than the previous 150hp 2stroke EFI Merc o/b I had on a 2001 model of same boat. Don't think the hull has changed much even since way back then. I've got a guy telling me that's what happens with an i/o on this boat, but it can't be. I had 8ppl on it (limit 11) and it creeped out of the hole and took at least 30 seconds to plane off. Even with just me, it's boggy on a hole shot, couldn't get a skier up. Best way to describe is it feels like it has a governor limiting power to 60%. Compression measured w/in spec just 2 engine hours ago. Wondering if could be a throttle issue b/c once you move the lever from 12o'clock to 10, the rpms don't change past that. Dead space so to speak. And tach SAYS it's at about 4200rpm when it maxes out, which also can't be proper. But not sure if I can trust the tach b/c the temp gauge on the tach never registers anything. Other factors: using trim gauge on multi function speedo, if you trim it up beyond barely north of the lowest line, it starts cavitating/racing. Prev owner put a hydrofoil on it. Speedo doesn't work so I can't tell you top speed and don't know if I can trust the trim since it's on the same gauge. 3 blade stock prop. HELP!

 

[Scott06]

Just bought 2016 Hurricane Deck boat SS201. This 250hp engine is weaker out of the hole and planing off than the previous 150hp 2stroke EFI Merc o/b I had on a 2001 model of same boat. Don't think the hull has changed much even since way back then. I've got a guy telling me that's what happens with an i/o on this boat, but it can't be. I had 8ppl on it (limit 11) and it creeped out of the hole and took at least 30 seconds to plane off. Even with just me, it's boggy on a hole shot, couldn't get a skier up. Best way to describe is it feels like it has a governor limiting power to 60%. Compression measured w/in spec just 2 engine hours ago. Wondering if could be a throttle issue b/c once you move the lever from 12o'clock to 10, the rpms don't change past that. Dead space so to speak. And tach SAYS it's at about 4200rpm when it maxes out, which also can't be proper. But not sure if I can trust the tach b/c the temp gauge on the tach never registers anything. Other factors: using trim gauge on multi function speedo, if you trim it up beyond barely north of the lowest line, it starts cavitating/racing. Prev owner put a hydrofoil on it. Speedo doesn't work so I can't tell you top speed and don't know if I can trust the trim since it's on the same gauge. 3 blade stock prop. HELP!

What prop are you running 4200 rpm at WOT is way too low. Should be 4600-5000. It could be as simple as the prop being incorrect and dropping 2" in pitch makes it work

look in the stickies at top of page there is a section on what to do if you have low WOT rpm.

WHile this boat is likely heavier than your old one it should do better than this, but the foil on it from PO tells me some thing wasn't right all along.

 

[Stinnett21]

Eight adults on a 20 foot deck boat is a load. I'd say Scott is right. To be honest there's no such thing as a stock prop. There's the prop the dealer installs to hopefully impress a potential buyer and that usually means top speed with a light load. Suspect you're running a 21" and you need to drop to 19" or maybe even 17" if that's a normal crew for you.

 

[poconojoe]

Use your phone's gps to monitor your speed.
If you dont have a way to do that, you can download an app specifically for that.

 

[sheltonoil]

Thanks everyone. Will check the stickies as well as the prop

 

[nola mike]

What prop are you running 4200 rpm at WOT is way too low. Should be 4600-5000. It could be as simple as the prop being incorrect and dropping 2" in pitch makes it work

On a new to you boat, the prop would be my last suspect. Imo much more likely that it hit correct rpm at some point in its life, but then developed a mechanical problem. You need to verify rpms, and probably at least change fuel filters and ignition components. I'd also double and triple check that your plug wires are installed correctly and in the right order.

 

[sheltonoil]

On a new to you boat, the prop would be my last suspect. Imo much more likely that it hit correct rpm at some point in its life, but then developed a mechanical problem. You need to verify rpms, and probably at least change fuel filters and ignition components. I'd also double and triple check that your plug wires are installed correctly and in the right order.

I will check those as well and I have wondered myself if changing the prop could make enough difference because the power lag seems so drastic. I will say that in my experience with cars, fuel filter and spark plug problems will generally result in stalls or misses, and this motor is doing neither of those. Starts and runs smooth as butter. Just isn't generating much thrust.

 

[sheltonoil]

Follow up. Turns out my prop pitch is 23, which I'm sure is killing my hole shot and planing time especially on such a stern heavy boat. Top end speed isn't a concern; is switching to a 4 blade 17" pitch too drastic? I can't find a readily available 18" pitch, just 17 and 19. Based on what I've read that I can expect a 200rpm increase per inch drop (which I know isn't a golden rule), seems like a 6" drop will increase my current max rpms (4200) a little over the rated max (5200) and a 4" drop will have me a little under. What are your thoughts on 17 v. 19?

 

[Bondo]

Ayuh,..... I'd probably go with the 19",.....

It's a pretty common size, maybe you can borrow one for a test run,.....

 

[sheltonoil]

Thanks, will do.

 

[Scott06]

Follow up. Turns out my prop pitch is 23, which I'm sure is killing my hole shot and planing time especially on such a stern heavy boat. Top end speed isn't a concern; is switching to a 4 blade 17" pitch too drastic? I can't find a readily available 18" pitch, just 17 and 19. Based on what I've read that I can expect a 200rpm increase per inch drop (which I know isn't a golden rule), seems like a 6" drop will increase my current max rpms (4200) a little over the rated max (5200) and a 4" drop will have me a little under. What are your thoughts on 17 v. 19?

What is current prop a 3 blade aluminum? Agreed staying with a 19” three blade or a 18” 4 blade like this if you want more hoelshot or focus on water sports http://boatpropellers.iboats.com/Michigan_Wheel-Vortex_XHS-Propellers/992203/?cart_id=252814407

 

[Cortes100]

FWIW, I had the 200Hp version of the 4.5L and all I can say it had lots of power, very smooth running engine. Mine was on a 18.5' glass boat and performed great. Fooled around with props and had excellent results with the Spitfire 4 blade 19 and 21P. Comparing with same pitch 3 blade Black Max, it was no contest and the spitfire out performed in every aspect. With the 21P, I could still tag the rev limiter at 4850 and in that 45-46 mph range. Used the 19P when we had a full boat and worked great for water sports.
The 250hp does limit at 5200 rpm.
Assuming everything is working properly, definitely testing a few props should keep you happy.