Hey guys. Just wondering if anyone can help me out. I recently bought a 1996 Nissan 40 hp tiller steer motor for my 1648 Grizzly duck boat. The guy I bought it from was running it on a bigger, heavier boat with no problems. I got the motor to replace a 25 hp mercury I had on the boat before.

Now, to my problem. The motor starts, idles, and runs great at low RPMs, but it takes a long time to get on plane (longer than my old 25) and actually runs slower than my old motor once it does plane out.

I've put a new fuel tank and fuel line on the boat. I've cleaned the fuel filter. Not really sure where to go from here. Any help would be appreciated.

Is it the same lower unit length than what you had? Also have you tried different tilt adjustments?

Yes. It has a 20" shaft, same as last motor and I've tried every tilt adjustment.

Just doesn't seem to be getting enough gas.

Might try some new plugs, and a shot of sea foam Before going any further. If that doesn't do it might need to have the carbs gone through

I would do a spark and compression test.

Ding ding ding best place to start

Thanks guys. Got the sea foam today. I'll get some new plugs this week and see if I can get it going this weekend. If that doesn't work, guess I'll take it in and let someone look at it.

Plugs, compression test, carbs. In that order. My money is on the plugs, especially if its been sitting a minute. I had a similar problem with my 25 when I first got it.

You need to actually check the spark, not just put new plugs in it. I think Ive only seen one bad spark plug in my entire life. There are a lot of other problems in the ignition system that can cause no spark, most of the time its not the plug.

You need to find out if its running on all cylinders, if its not your a short while away from cratering it.

Ok. So I checked the compression today. 130 on both cylinders. Perfect for all I've read. Both plugs are sparking when you turn the motor over (assume that's what you guys mean by spark test) but I'm going to replace them anyway.

So... Tomorrow I'm going to:
1) Put hose clamps on all the fuel connections to make sure no air is getting in.
2) Empty the gas tank and replace with new gas and make sure the mixture is perfect (50:1).
3) Add 2 oz of sea foam per gallon (12 oz total) to the gas.
4) Back the boat into the stock tank, crank it, and spray sea foam into the carburetor (this is different from the type that goes in the gas) for several minutes.
5) Replace the spark plugs with new ones.
6) Take it for a spin.

If I'm doing something you wouldn't suggest, or missing a step please let me know. Otherwise, I'll let you guys know what happens.

Again, thanks for all the advice.

Email Steve @ Steve's Custom Props with what prop you have and info on your boat. Might be a prop issue since the other boat was bigger.

So, I did everything on my list plus pulled the carburetor and cleaned it. No noticeable change. Guess the next stop is the shop.

As for the prop issue, I really doubt that's it. If the prop were too big, it would have trouble getting up, but it would be great on the top end. If it were too small, it would shoot out of the hole but lag behind on the top end.

It's slow getting up and slow on the top end. Plus it has a rough idle. I'm really at a loss. The only other thing I can think of is a timing issue....which I have no idea how to address.

I'm having a very similar issue right now with my Johnson 40. The only difference I've noticed with mine is a shaking feeling during acceleration, are you having that as well? It stops once at full throttle and doesn't shake at idle either (or at least not noticeably)

I'm stumped. You did everything I would have. Compression is fine. Maybe pull the prop and make sure there isnt any fishing line wrapped around the prop shaft (also ruins prop shaft seals)? Aside from that, could be a timing issue, but I kinda doubt it as it would be running rough through all RPMS. When you cleaned the carb, did you fully break it down and clean all the jets?

Been a while since I updated this, so here goes. Ended up taking it to the shop and they said it needed a new carburetor, so I had them install one.

That solved the rough idle issue but did nothing to help the power. I'm living with it right now, but will probably just replace it with a 50 hp soon.

But, please... If anyone has any ideas, let me know.