New Power-Head problem

Just replaced the power-head on a 2001 Johnson 115hp Ocean Pro. I was following the break in procedures supplied with the motor. 1st hour I was to run the motor at no more than 3000rpm and vary the throttle setting. All went fine for the first hour. The second hour called for and increase in rpm to no more than 4000rpm and to vary the throttle. After about 10 minutes of running between 3500 & 4000 I brought the throttle back to 2000 and in the decrease heard knocking coming from the motor. I turned towards the dock and brought the motor up to 3000 and back down and the same knocking sound. The motor powered up fine and there was no knocking sound in the increase of rpms only when you slowed. I shut the motor down and coasted to the dock. I removed the plugs and the piston tops look fine, I used a dow to push on the pistons to see if rods were loose and there was no play. I premixed 50:1 in the fuel tank before starting along with the oil injection. I did notice a small chunk missing out of a blade on the prop after getting it home. Any Idea on what could be the culprit of the knocking(sounds like a rod knocking in a car motor)? There is a little play if you pull and push in on the prop. Could something in the lower unit have gone bad? Any ideas would be a big help.

Re: New Power-Head problem

It could be in the lower unit but lets look at something first. <br /><br />It could be what the engineers call "de-cell knock" in the 60 degree motors. It can be very loud and sounds like a rod coming loose. It happens when you cut the throttle suddenly. <br /><br />What spark plugs are you using? What grade fuel?

Re: New Power-Head problem

Plugs are Champion QL78YC<br />Fuel is 87 octane with mix 50:1 TCW-3 for piston break in

Re: New Power-Head problem

OK, good. The next time you de-cellerate try pushing in the primer momentarily. If its de-cell knock the extra fuel will make it go away. Slightly cooler plugs like the QL77JC4's may help a tad too. But youre OK with those plugs and fuel.

Re: New Power-Head problem

By primer do you mean the choke on the ignition key or pump the fuel bulb??? Not sure where the primer is.

Re: New Power-Head problem

Yes, its what you refer to as the choke. The primer actually injects a shot of fuel into the motor.<br /><br />Let us know what happens.

Re: New Power-Head problem

DHadley..you helped me in the past with this motor (in Feb of this year)and I appreciate your knowledge & expertise. In our past conversation about this motor the reason I posted was that the #1 piston had a hole the size of a half dollar in it and we were trying to figure out what may have caused it..and what to do about it. Well I went ahead and got a new powerhead for it and had the timing set. The old timing was set to 30 degrees which I was told by a mech. as being 10 to fast. Which lead us to believe that is what caused the hole, never actually figured out exactly if that was the cause. I am just worried that something may be resurfacing in the new powerhead that could be caused by the transferred components from the other powerhead. Maybe I am just a little leery now after just spending sooooo much on replacing the powerhead. Does the de-cell knock hurt anything and should I run it with the water ears to it on land or put it in the lake?

Re: New Power-Head problem

I'm glad you are concerned about finding the cause, a lot of folks think a damaged piston was the cause. Good for you.<br /><br />Yes, an extra 10 degrees would absolutly burn a piston!!<br /><br />The de-cell knock doesnt seem to hurt anything. And some 60 degree motors do it, some dont and some do it worse than others. <br /><br />Let us know if the primer deal helps. Im almost sure thats what it is but lets make sure. It wouldnt hurt to let your builder know too.

Re: New Power-Head problem

Great, thanks. I will run it Tuesday and see if that helps and let you know. If I go to the QL77's what would be the gap?

Re: New Power-Head problem

Anywhere between .030 and .040. .040 may idle better. Actually on my 60 degree 150 I run them about .035. I dont fool with the gap a whole lot to be honest.