J14 w' 25hp Mercury 4 stroke not planing

[blankenship_kevin]

I just bought a 1998 Carolina Skiff J14 with a 1999 25hp Mercury 4 stroke bigfoot. I am running the original merc/quicksilver 12 pitch prop and I just had it reworked to new condition by a local prop shop. I took it out yesterday and could not get it to plane with me and a buddy in the boat. I kicked him out and still had no luck by myself. Top speed was around 10mph. I also played around with different trim adjustments and that didn't help either. Is there something wrong? Thanks!

 

[Home Cookin']

Re: J14 w' 25hp Mercury 4 stroke not planing

yes you are not running on all cylinders.

I assume the motor felt like it was running full speed?

Was the hull fairly level, or plowing the bow, or dragging the stern? Could be that the angle of the motor is wrong--try different trim.

When my carolina skiff is loaded and won't get up I drive over shallow water to get it up, but in your case you shouldn't have to.

 

[blankenship_kevin]

Re: J14 w' 25hp Mercury 4 stroke not planing

yes you are not running on all cylinders.

I assume the motor felt like it was running full speed?

Was the hull fairly level, or plowing the bow, or dragging the stern? Could be that the angle of the motor is wrong--try different trim.

When my carolina skiff is loaded and won't get up I drive over shallow water to get it up, but in your case you shouldn't have to.

To me it felt like it was running full power but this is my first 4 stroke. I just took the boat/motor over to the prop guy and said the set up looked great. Prop, trim, etc. looked right. It is more or less dragging the stern. It acts like it doesn't have quite enough power to go ahead and flatten the boat out. You think it may not be running on all cylinders? I will check that this evening. Thanks!

 

[Mel Taylor]

Re: J14 w' 25hp Mercury 4 stroke not planing

I know you said that you just had the prop reworked, but is it possible that you have a spun prop? That would let your engine rev up but would cut your speed dramatically. Eventually you wouldn't be able to move at all.

 

[WN2712NJ]

Re: J14 w' 25hp Mercury 4 stroke not planing

If this motor is like the 9.9HP Bigfoot that I used to have, it has a 4 blade prop with flat pitch, and a transmission with lower than normal gearing. And a rev limiter set lower to boot. Great for pushing a big boat at trolling speeds, but really bad for moving a small skiff fast. Our Bigfoot would not plane our 14 foot tinny. It would hit the rev limiter when we tried. I bought a 3 bladed "speed" prop (actually, it looked just like the prop used on the non-Bigfoot motors) and suddenly it would plane with just one or two in it. We ended up selling that motor and getting a Tohatsu 20HP for the boat. Pretty much the same powerhead, but (I guess) a bigger carb and higher rev limit. And gearing and prop more amenable to pushing a skiff. Does 20MPH fully loaded 26-27 lightly loaded.

-dm

 

[Silvertip]

Re: J14 w' 25hp Mercury 4 stroke not planing

Big Foot motors generally have 20 inch legs. On a 14 foot tinny that may be part of the problem since the long leg creates drag and creates a gosh awful lever that tends to bring the bow up and the stern to dig in.

 

[Home Cookin']

Re: J14 w' 25hp Mercury 4 stroke not planing

tell us where your cavitation plate is compared to the bottom of the hull. I bet the J14 has a short shaft transom

 

[blankenship_kevin]

Re: J14 w' 25hp Mercury 4 stroke not planing

tell us where your cavitation plate is compared to the bottom of the hull. I bet the J14 has a short shaft transom

I will need to look at it this evening and measure or take a pic. I took it over to the prop specialist and he seemed to think that it all looked great and that everything was set up properly. It is running a 3 blade 12 pitch prop and I am not sure of the diameter.

 

[blankenship_kevin]

Re: J14 w' 25hp Mercury 4 stroke not planing

Also, I borrowed a tach from an auto mechanic friend of mine. It is a Fluke auto meter. I am not sure that it was getting accurate readings because at idle it showed around 2400 rpm. WOT was around 8400-8500 RPM. According to what I have read and seen specs on this motor this is very high. Also, I could only get an RPM reading on the top cylinder. I mentioned that to my mechanic friend and he said it might be that the coil firing positive on one cylinder and negative on the other. Just his guess since he is an auto mechanic and not a marine mechanic. I also think it is running too smooth to only be firing on one cylinder. I also ran it with just me in the boat and it planed great and achieved around 24mph. Is the motor just borderline for the boat? It is only rated 40hp max.