2001 50 Nissan not consistent at WOT

[paperduck]

I have 2001 50 Nissan tiller handle motor. The motor runs at different speeds at WOT. Most of the time WOT is 37mph, but sometimes it will jump up to 40mph. It will hold 40mph as long as keep it wide open but if you let off it will not go above 37mph. I had a 40hp on the boat before and it would do 37mph so I think 40mph is probably where this 50hp should be running at WOT. Could an air leak be causing the problem and how would I find the leak. Thanks for any information

 

[suzukidave]

Re: 2001 50 Nissan not consistent at WOT

I think it's a trim issue. My 55hp suzuki used to do the same thing. Sometimes it climbed out to a better top speed than others but I could never do it reliably. I figured it was a trim issue since my rpm didn't vary. Since I don't have power trim and varying the manual trim didn't help I put some trim tabs on the boat. Now it is consistent (and faster).<br /><br />Your boat top speed is not a direct function of HP by the way. It's a function of RPM at the prophub times the propellor pitch. More HP means you should be able to turn a higher pitch prop at the same rpm as the 40hp and go faster. The gain may be marginal between some 40s and 50s, but you may be underpropped if your 50hp is no faster than another 40hp on the same boat. Do you have a tach?

 

[paperduck]

Re: 2001 50 Nissan not consistent at WOT

The rpm's do change along with the boat speed. I don't have a tachometer with this being a tiller handle motor but I am using a handheld GPS to get the speed. I am running the same style Powertech Prop but it is a 15 pitch where I was running a 13 pitch on the 40hp. I have noticed gas leaking from the top carb. apparently from the bowl gasket and I am going to replace it and see if it helps.