1982 Mercury 80 hp

I am not a boat mechanic but I am good with tools. I just purchased a pontoon boat which came with an 1982 80 hp merc. I have noticed one time you start it it will run great. The next time it may run fine or it may idle high and act like it is not firing on all cylinders. I can watch the tac and when its running well I'm at about 5k when it is messing up 3k is the best it will do unless i keep hitting the choke. I replaced the fuel line, primer bulb and added an inline filter. I have gone no further other than getting a service manual for it. I also noticed it is sporting a plastic prop which I am not too keen on, seems like it would tend to flex way too much so it will be replaced and saved as a back up. Thanks for any advice on which way to go.

 

You should buy a workshop manual for this engine, if you intend to do work on it yourself. You will find troubleshooting easier that way.

 

That would normally indicate carburetors that are clogged or an air leak. Most probably they need to be rebuilt.

 

I was thinking fuel more so, a lack of it since I can hit the choke and it picks up. I hate to chase intermitant problems

 

Could be a sticking needle valve, could be many things, but without a manual, it is more difficult.

 

The very first part you buy for your new boat. It'll point you into the neighborhood where the next round of parts buying will live.

Sounds like you have contaminated fuel and/or fuel delivery system. Standard fare on a used boat. Replace the consumables, clean the full system (hoses, bulb, tank, filter, carbs, etc.). In all honestly, you should probably replace the hoses, clamps, filter, bulb, etc., given you don't know their age (never believe the previous owner) and any one of these things could be shedding little bits of gunk, into the system. This way you start with a level playing field and know the quality and life expectancy of each element.

 

It could have old style hoses that are not ethanol resistant.

 

I replaced the hose from tank to fuel connector along with the primer bulb, between the primer and the engine connector I added an inline filter. Made no change

 

The hoses between the pump and the carburetor should be changed too.

 

I change out a lot of this sort of thing. If the boat has any age, the fuel system needs an overhaul. The carbs are likely clogged with gunk and bits of ethanol dissolved rubber. They need to be completely taken apart, cleaned, new replacement parts installed and tuned up after they're back on. The whole of the fuel system needs to be cleaned, new lines, clamps, filters, everything. It only takes a few years of neglect to force this issue.

Then again, you could be experiencing other issues, like non-functioning advance or other concerns. The manual will nurse you through the basic tune up and spec checking procedures. Once you have a level playing field, you can determine what else you need to do.