Motor Question/Advice

Just wanted to ask some opinions since I've only owned a boat since April. It's a 16' flats boats with a Tohatsu 40hp 2 stroke motor...as a flats boat, I fish a LOT of skinny water, so mud and sand get sucked up pretty frequently. I'm pretty good about shutting it off as soon as I notice and poling into deeper water to flush it back out. I had the impeller replaced in May shortly after buying the boat after clogging it up in Mosquito Lagoon...well, I think it's happening again. Yesterday it was running a bit rough and just peeing spurratically at idle. When it has some throttle I get a nice steady stream still. I also noticed a little bit of steam coming out the back vent, which to me indicates overheating. I never heard the buzzer go off, but the engine shut off a few times (could have also been because my fuel was low and the chop was rough, it doesn't take much to make my boat tilt drastically). I brought it home, put the muffs on and started to flush it. I noticed white smoke out of the prop exhaust and I've never seen it do that before.

My buddy at work services his own boats and told me to just take it apart and replace the impeller and thermostat. I've worked on cars enough to be mechanically inclined, but I've never worked on this boat besides minor maintenance. I called the guy I bought it from (owns a marina) and he recommended I bring it up to his shop today after work. My question is...based upon what's happening, should I try myself to just replace the parts that usually indicate overheating? Should I first take it to a freshwater lake and run the crap out of it to try and flush whatever is in there? Or should I suck it up and take it in to the shop? I don't expect I'll be raped on this ordeal, but as with any repair shop, labor costs are a bitch.

Sidenote: I took the prop and found a good bit of braided line around the shaft. With that taken out, it could run much smoother on idle.

 

Bump! I'm thinking I can do the water pump repair kit myself and while everything's apart I can clean out the vents, etc.

 

How did it turn out?

I just noticed your thread. Water impellor replacement is easy & takes about 2 hours on my 175HP. Saves you a ton of money to learn to do it yourself. I would get your buddy to show you how.

I posted a write up on how to replace the impellor for Mercury, Evinrude, & Johnson. http://www.tacomaworld.com/forum/bo...acing-your-water-pump-impeller-your-boat.html

 

I had the shop guy look at it and he tested the compression, stating I had bad compression in #2...he also said the head gasket was damaged. Few hundred in parts and labor and I got it back...needless to say, it happened again (sometimes I hate mechanics). Rather than dump more money into his pocket, I decided to do the following: complete water pump rebuild, changed the oil, new plugs, and cleaned the carbs. I also bumped up the idle a tad and it runs really well now. Just in the last few weeks it has started bogging down when I'm at higher rpms...it will just bog momentarily then surge back up. Seems like another fuel issue; perhaps some trash in the lines or jets? I plan to take it to a different shop that will diagnose it for $60. I wouldn't mind tearing into it myself but I will end up replacing things by process of elmination and cost myself more in the long run.