Mercury 175 slower than expected?

**blackmaxonly** · 08-26-2021, 08:52 PM

Hey guys, long time lurker but decided to finally dive in and get some opinions.

I have a 1983 Checkmate Eluder 18.5' with a 1978 Mercury 1750 175hp motor (crank rated, ~150 at the prop). I just recently got it put on the hull and am surprised by the lack of speed I am seeing on the GPS. The motor turns at ~4900-5000 WOT and the top speed I got on the gps was 44 or 45mph. Does this seem correct? For reference I have a 1991 searay 160 with a 1991 merc 115 that also does 43-44mph.

Research online tells me the hull is 1100lb unrigged, and close to 1800lb all said and done. The boat idles just fine, it has some hesitation / bogging when you put the throttle down so you have to ease into it, other than that it seems to run just fine. I also installed a clear piece of hose to look at the fuel after the bulb, and it looks like a solid stream, a few bubbles here and there but very very small.

Let me know what you guys think, or if I'm just being unrealistic with the speed I was initially expecting out of it

**Capt j** · 08-26-2021, 09:15 PM

Your dealing with a motor that's over 40 years old. It might only make 100 hp these days. Sounds like your overpropped. Those old 2.4's needed to make RPM's in order to make power. Try getting RPM's up towards 6000.

**blackmaxonly** · 08-26-2021, 09:27 PM

Yea the motor is really old, just had new rings put on. I fear I was overpropped, even though it seems like it should handle a 19" aluminum prop

**David - WI** · 08-26-2021, 10:41 PM

Either the boat is heavy (water-logged or full of unneeded junk) or the motor is not making power... gotta be a 60 - 65 mph boat.

https://m.youtube.com/watch?v=PdwQS-iMFwU

**blackmaxonly** · 08-26-2021, 11:05 PM

Originally Posted by David - WI

Either the boat is heavy waterlogged or full of unnecjunk) or the motor is not making power... gotta be a 60 - 65 mph boat.

https://m.youtube.com/watch?v=PdwQS-iMFwU

Thats one of the videos that I got my prediction from! It seems like everyone with a similar setup is running atleast mid 50s, and 60+ with a jackplate. Meanwhile I'm struggling to hit 45 with a simple 19" on castle rock. Brand new stringers and deck, glassed over as well So I can confidently say there is 0 water in the hull. Im thinking maybe a cylinder or 2 are down at WOT, but I have clean spark at idle

**Revenge22** · 08-26-2021, 11:26 PM

always mystifies me when mechanics re-ring an already tired motor. bore/hone for a motor that old I say... could have terrible leakdown. not that yours was tired , just a possible explanation !

**tlwjkw** · 08-27-2021, 02:58 AM

comp?.. leak down?.. all 'lectrics checked?.. carbs clean with all new gaskets?.. fuel delivery after mech pump?.. link/sync?.. all these things need ta be checked/done.. if they are good go here for initial motor set up.. Frequently asked questions and answers about Boat Propellers, Custom Props and Boat Propeller (stevescustomprops.com) look for a min. of 5800.............. jmo.

thats a 2.0 motor and with its age needs all tha help it can get.. do ya have an OEM manual for it?

**blackmaxonly** · 08-27-2021, 10:47 AM

Comp is all 110-115 across all 6 cyls, carbs were fully cleaned and new gaskets in all, and timed with a light according to the manual (20* max, 14*atdc idle). Im thinking its a miss but it doesnt sound like anything is wrong at speed. I will get to testing this weekend and see what I can figure out!

**tlwjkw** · 08-27-2021, 11:03 AM

is idle stablizer still on it?.. if so it probably needs go away... as for tha idle hesitation do this.. with all adjusments done you need ta have a very slight gap between tha throttle cam and roller.. this can vary depending on what you want it (motor) ta do.. this will allow advance timin' a tad before carb throttle.. helps a little with some and a lot with some.. also set "idle timing" with boat in tha water, in gear under a load.. numbers here will not mater.. jus whatever it ends up that makes you and tha motor happy... gl.

really sounds like its runnin' on 5 instead of 6 for whatever reason.. should spin tha 19 alum. easily if all else is close..

**tlwjkw** · 08-27-2021, 03:40 PM

because it actually works....... if your way works for you then thats great...

**tlwjkw** · 08-27-2021, 03:56 PM

never said it was tha right or wrong way.. jus said it works..

**tlwjkw** · 08-27-2021, 06:33 PM

Originally Posted by Whaaaaat

Please show me in a mercury manual where it says this.

best i remember it says in tha water, in gear.. ta me that would be under a load.... can be on tha trailer.. doesn't need ta be goin' down tha lake.... ya jus guessin' ta start with anyway.. it gives ya about 8 ta 9* ta play with on idle timin'............

**Whaaaaat** · 08-27-2021, 06:57 PM

Originally Posted by tlwjkw

best i remember it says in tha water, in gear.. ta me that would be under a load.... can be on tha trailer.. doesn't need ta be goin' down tha lake.... ya jus guessin' ta start with anyway.. it gives ya about 8 ta 9* ta play with on idle timin'............

I was 100% wrong. My apologies. I skimmed what you had said and confused it with a thread from not long ago where a guy was telling people to adjust wot in the water in gear. I should've read your post completely.

Manual does say to verify timing adjustment of base idle in gear and warm. Adjust to stable idle .

I'm going to delete my previous post, I don't want to confuse anyone.

**tlwjkw** · 08-27-2021, 08:37 PM

no problem bud.. it happens... jus as guilty of it as tha next guy... don't remember if its in all are jus some of tha manuals...

i can see where doin' that would be a big problem...

**mrichartz** · 08-27-2021, 09:44 PM

Originally Posted by Whaaaaat

I was 100% wrong. My apologies. I skimmed what you had said and confused it with a thread from not long ago where a guy was telling people to adjust wot in the water in gear. I should've read your post completely.

Manual does say to verify timing adjustment of base idle in gear and warm. Adjust to stable idle .

I'm going to delete my previous post, I don't want to confuse anyone.

Which that guy mistook for omc motors ? They need WOT in gear unload at rpm... Thats omc.