Nissan 5hp Outboard - solved strange problem

Article By Shorty

Really Strange Outboard Problem

A freind of mine was given this Nissan (Tohatsu) 5hp, 2 stroke, long shaft outboard motor. It has previously lived and unknown life, what was known is that it would start and idle, but not rev up to any speed.

From what I have read, Tohatsu makes the outboards, Nissan puts their sticker on it and marks it up a bit and that is the only difference.

Nissan Marine
Tohatsu Outboards

My friend tried to fix it, but couldn't figure out the problem and was considering throwing it in the trash, so he gave it to me saving him a trip to down his driveway to the curb. I really needed an outboard for my O'Day, but didn't have the money to buy one, and I don't know how to fix them - but figured with a free outboard I didn't have anything to loose by trying to fix it up. Besides it is a 2 stroke, and numerous people have told me they are the easiest engines to work on.

I had a fantasy that the outboard would know it landed into caring hands and magically start working, but it didn't. When I fired it up in a bucket of water, sure enough it had the same problem, I could get it to idle, but not go above idle. Also on the back of the water jacket (up high) were 2 small holes. Water would spray out of these holes with the exhaust, looked kinda strange but figured that is how this outboard must run.

The general consensus is that it must be the carburator. A neighbor down the street came to help me, we completely dissasembled it and he sucked & blew on all the parts, and put them back together again. We ended up with a couple of spare parts that I never figured where to re-attach, he said didn't need them so we moved on. The engine ran just the same, no better or worse than before. Leaning over the open gas tank with a cigarette in his mouth, he shrugged his shoulders, opened a beer and said he had no idea what the problem was, and referred me to a small engine shop. Not ready to spend the money on this motor yet, I wanted to try some more research and work on my own.

Another friend of mine told me that no matter what, first thing I should do is replace the impeller. The what? So he talked me thru it on the phone, I was able to remove the lower unit, then unbolt the water pump shown here. The impeller is the rubber thing that spins in the middle which pumps the water.

When I pulled the old one out, I noticed that one of the blades had broken off and was blocking the hole which led up to the engine -- HA! this might be a culprit.

This photo shows the side of the water pump. The pipe on the bottom is the draw tube that sucks up fresh water, then the rubber impeller pumps it in the housing and it heads up the tube that is facing into my index finger.

Here is what the top of the lower unit looks like, with the water pump removed. It was completely full of muck, grease, dirt, all sorts of stuff. This photo is after the cleaning.

Putting it back together was a real chore, there are 3 things that have to line up to get it to fit. 1 - drive shaft, 2 - water line, 3 - shifter linkage shaft. After many swear words, I was able to get it back together. The hole in the side of the water jacket is an access hole to put together the linkage from the shift lever to the lower unit, to change gears.

I fired up the engine again and it would run a little better !! Still wasn't going up to speed, but I was making progress. I took the pump apart again, and re-assembled - was still just a little better, but so far from what it should be.

With all of the gunk removed from the water jacket, the water would squirt out near the foot, and the exhaust was the only thing that would come out of the 2 holes at the top of the water jacket. So I started thinking more about heading down to a professional mechanic, and was running it one last time. I noticed that there was a lot of exhaust coming from the rubber seal over the access port. (in this photo the the access port is shown empty, without the cover on it). So on a hunch, I pulled the cover off and gunned the engine. WWWHHHHHHEEEEENENENENENENENEeeeeee...... !!!!! Ureka !! The exhaust has nowhere to go and is trapped in the water jacket!

So I pulled the prop off again and dug around in there. A bunch of shells came out, then more with gunk attached, and finally I sprayed in there with a hose to open it up more. With the gunk removed, I put it all back together and she runs great now.