25hp Mercury is Sloooow.

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TinCan2

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I'm trying to bring a 1989 Merc back to life. I rebuilt the carb and tuned the motor up. Crazymanme2's advise fixed my starter problem (bad solenoid), thank you. Now the problem is no speed. Motor starts fine and runs good, but there is no speed. I know I'm pushing a bigger boat (1648 Seark) but would think I would get a little more speed. On today trip boat would not even plain out. I would estimate speed at around 10 to 15 mph on todays trip. At full throttle it seams there should be more in the tank, doesnt seam or sound like motor is wound up all the way. Is there something I can do?
 
Need some more info,as where is your tilt pin position,look down the throat of the carb to make sure your getting full throttle,how loaded down is your boat,maybe a pic of the motor on the transom,(side pic)did the motor ever run good? :?:
 
We will see if this picture attaches. If so it is a copy of my setup. Motor tilt pin was on the third hole from the back. I moved it to the fourth, haven't tried that position yet. Boat weight is 297lbs. I have added gear (batteries, fuel cell, tackle, etc) of an estimated 160lbs plus my weight of 190lbs, so weight it is pushing is an estimated 350lbs. I looked and the paddle in the carb is exactly horizonal at full throttle. I just got the boat (it was given to me) and dont know how it ran before. As you can see it is the long shaft.

I thought about could be firing on one cylinder, will check it this evening. Any pointers on the easiest way to do this?

Feel like I am replacing the motor one part at a time!
 

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TinCan2 said:
We will see if this picture attaches. If so it is a copy of my setup. Motor tilt pin was on the third hole from the back. I moved it to the fourth, haven't tried that position yet. Boat weight is 297lbs. I have added gear (batteries, fuel cell, tackle, etc) of an estimated 160lbs plus my weight of 190lbs, so weight it is pushing is an estimated 350lbs. I looked and the paddle in the carb is exactly horizonal at full throttle. I just got the boat (it was given to me) and dont know how it ran before. As you can see it is the long shaft.

I thought about could be firing on one cylinder, will check it this evening. Any pointers on the easiest way to do this?

Feel like I am replacing the motor one part at a time!


Easy way is to pull the plugs and ground them to the motor, crack the motor and if it sparks then you are good. You can also get a spark plug tester, which is the preferred method.
 
Looks like your cavitation plate is well below bottom of your boat.Your boat might be designed for a short shaft, which with the shaft so far in the water would create more drag.
Make sure your motor is firing on both cylinders as mentioned before you mess with the tilt & height of the motor.
 
Had a friend look at the timing advance. He got a little umph out of it. He also suggested I raise the jack plate atleast another 3 inches. Will try that and let everyone know how that works. Checked and it is definantly firing on both cylinders.
 
Ok, got home from work tonight and lifted the jack plate three inches. Put hotter NGK plugs in it and motor seams to run a lot stronger. Will have to throw it in the lake tomorrow to let you know how things worked out.

Attached picture shows the motor after the jack plate was lifted three inches. Does this look like it will be enough? Will have to do some fabrication work to take it any higher.
 

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I have a 1" thick piece of hardwood on top of my TH Mini Jacker to raise the motor a little more.
 
lckstckn2smknbrls do you think it needs to go higher? I could do the wood think. I'm an accountant for a large metal fabricator/manufacturer. I have the materials and labor available to lift the transit out of AL if needed. I like the durability of AL better; but, I'm sure your suggestion will be fine. Thanks you for the input, I appreciate any ideas.
 
TinCan2 said:
lckstckn2smknbrls do you think it needs to go higher? I could do the wood think. I'm an accountant for a large metal fabricator/manufacturer. I have the materials and labor available to lift the transit out of AL if needed. I like the durability of AL better; but, I'm sure your suggestion will be fine. Thanks you for the input, I appreciate any ideas.
Aluminum would be better I had the wood sitting around. My anti-cavitation plate is about 2" above the bottom of my boat. You can raise your motor a 1/4" higher for every 1" you have it set back. The Mini Jacker has a 4" setback.
 
I took the boat to a local lake last night to try the motor with current setup. Results were a lot better. Plained out and ran faster than it has ever. I estimate the top end speed to be in the low 20s mph. I don't have a way to check actual mph. At top end of the throttle the waterline on the motor was at the bottom of the (I guess cavitation plates) two rings/plates just above the foot (see photo above). I know this is a lot of boat for a 25hp. Do you think it could do better on speed or am I at the max? Good news is I can live with its current output. More speed is always better if you can get it!

I attached photos of the "trail" the boat was cutting and a picture of boat for size reference. Does the "trail" look about right?

Everyone please excuse me, I'm new at rigging tin boats. In the learning curve. I appreciate everyones help.
 

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  • trail.JPG
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That motor is plenty for that boat, but without having a mph reading its hard to tell if your getting everything out of it. The motor setup looks like the cavitron plate is still a little low according to Lock and Stocks....
 

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