80HP Mercury bogging down.. Please help!

[Iampan]

Hi guys, I have an 80 HP mercury outboard serial number 5583059. The motor is on a 1980 champion 16ft bass boat. I can?t find any information about this motor. This is my first boat and motor and brought it out for the second time today. I have noticed that it is a little rough to start and stalls every once in awhile while in idle. My problem is that the boat goes very nice up to 4,000 rpm. When I open the throttle completely it goes good for a few seconds and then the rpm bounces up and down like its losing power and regaining it. It will do this until I manually bring the RPM down near 2500-3000. After that it runs fine again. I can run the boat at 4,000 or under without a problem. I just ran some seafoam through the gas and didn?t do anything. I am new to this and hope it?s something easy to fix. If I can?t do it myself I don?t want the boat shops to take advantage that I don?t know much. My father in law has been a car mechanic for 30 years and owns a boat so he knows some. He didn?t have any ideas on this though. From what I have read on here it may be something to do with the carbs or fuel. How and what should I check for if even that?

Any help would be appreciated. Thanks guys!

 

[ONERCBOATER]

Re: 80HP Mercury bogging down.. Please help!

suggest before you go any further you get a genuine mercury manual for that engine.
we can go fro there much easier. that way you will have a referance and a companion for the long haul... and your father in law (30yr mech) should be able to easily digest both what we are saying and what the manual says.. then you two can work on it together. And we can clarify things if needed.

My gut instinct on this one would be remove, tear down and clean carbs....rebuild em... then perform a link and synch and adjust fuel mixtures to optimum settings. For that a manual is priceless. that said...you can purchase a manual from this site, ebay, or anywhere else that pleases you, preferance for the real merc manual for your engine rather than the Seloc manuals.

Sean

 

[Chris1956]

Re: 80HP Mercury bogging down.. Please help!

The carbs may be dirty, but I would first check for a restriction in the fuel supply. Look up the serial number at the maxrules.com website, to get the year. Then inspect the fuel filters, and anti-siphon valve in the tank. If they are clean then rebuild the fuel pump. After you have run her a while look at the spark plugs. If they are lite to dark brown, the carbs are probably OK. When was the last time the waterpump was rebuilt? That is always a good idea.

 

[carholme]

Re: 80HP Mercury bogging down.. Please help!

That s/n comes up as a model 1080520 from Mercurypartsexpress, and that model comes up as:

1080520 MERCURY 1980 80

Parts Listing:

http://www.crowleymarine.com/mercury-outboard/678.cfm

Mercury service manual 90-86134--4

Gerry

 

[Iampan]

Re: 80HP Mercury bogging down.. Please help!

Cool I'll def try to check the simple things before redoing the carbs.. The impeller and all of that was replaced a week ago because it wasn't peeing at all.. So to check the spark plugs just pop off the cover and pull them out after it has ran a bit? I want to do this with the motor off right? I will also inspect the fuel lines and all of that in the next day or two. When it is bogging down some if I push the choke in the rpms do move up a little bit for a quick second. I don't know if that's normal or not. The problem with my FIL helping is actually getting him to come over and help.. So it will take me a little while to figure some of this out, but I will try everything you guys tell me.

Thanks

 

[westjr8]

Re: 80HP Mercury bogging down.. Please help!

Iampan,
It sounds like to me its a fuel/line problem. Being that the rpm's shoot back up when ever you choke the engine while running. I would check you gas tank, primer bulb, fuel pump, and all hoses for wear/tear. Also, I would certainly clean the carbs out and make sure the needle/floats are set right!

 

[CharlieB]

Re: 80HP Mercury bogging down.. Please help!

Ditto the fuel pump rebuild and replace all old fuel lines.

You are running at the limit of the fuel flow from the pump and hoses.

Continuing to run like this is guarenteed to melt pistons as the carbs are not FULL at WOT.

 

[Iampan]

Re: 80HP Mercury bogging down.. Please help!

So I should not take the boat out until this is fixed? Or should just not run it above 4000? Is this something that I can do without knowledge of any of this or should I take it somewhere? Can someone tell me by chance exactly what I need to buy to do this. Like I said I can not find my motor serial number anywhere and want to purchase the right things I need to fix this..

Thanks guys,
Jason

 

[Iampan]

Re: 80HP Mercury bogging down.. Please help!

Ok I talked to FIL today. He and I are going to go over the fuel lines and all of that tomorrow. I'll post back then and let you know how it went

 

[fisherguy123]

Re: 80HP Mercury bogging down.. Please help!

I had that problem using the old metal fuel tank that came with my 82 merc 50 hp......the metal pick up line inside must have had pinholes in it so i scrapped the tank for a new one and changed the flex line too.......no problem after !!!

 

[westjr8]

Re: 80HP Mercury bogging down.. Please help!

Pan,
The motor serial number should be on a data plate somewhere on your engine. Mine is located on the port side, on the middle unit. I would recommend a fuel pump gasket kit ($8), and a carb kit ($50). If you have an old metal gask tank, I would also recommend switching that out with the newer plastic tanks. Fuel lines arent expensive either. This is something you can certainly do yourself if you just pay attention to the parts you take apart! And you are right, DO NOT take the boat out at all until you fix the problem. If you continue to run your engine without the proper fuel supply, you run an extremely high risk of overheating and melting a piston.

 

[Iampan]

Re: 80HP Mercury bogging down.. Please help!

Ok we replaced all of the fuel lines. The connector to the gas tank seemed loose also before we replaced it. There was a little gunk in the first few inches of the line. FIL checked out the carbs from what he could see and said they appeared to be pretty clean from what he could see. Probably won't be able to get the boat out until mid week since it is so cold here. Been around a high of 34-35 last few days.

Couldn't find a fuel filter though. Found a little gas line on motor running to a strainer - screen looking thing. It was round and sat flush in motor and was fairly small. Not sure if this is it or not. Also bought and replaced the gas tank fittings. I am using plastic gas tank right now also. I really hope after seeing some blockage in the line and the connector not being really tight that this helps...

Thank you all for the help and I will def post back soon and let you know how it goes on the lake.

 

[westjr8]

Re: 80HP Mercury bogging down.. Please help!

The loose connector certainly can be the cause of your problem. The gunk in the lines can also have a huge impact. I would still recommend taking apart the carbs and cleaning them. If there was junk in your fuel lines, it is very possible some of that same junk is in your carbs. Take my word, you much rather spend a few hours cleaning the carbs than spending hundreds of dollars replacing a burn up piston!

 

[CharlieB]

Re: 80HP Mercury bogging down.. Please help!

You didn't mention rebuilding the fuel pump.

Test the fuel pump FLOW by removing the fuel line to the carbs, point it into a suitable container and crank the motor. You shouuld see a STRONG pulsed stream, any less and you loose WOT RPM due to running LEAN and start melting pistons.

The fuel pump rebuild kit a WAY cheaper than even one piston.

 

[Iampan]

Re: 80HP Mercury bogging down.. Please help!

Ok guys after switching all of the fuel lines, primer bulb and connections it seemed to do the trick. Took the boat out today and it started quickly and ran at WOT nice and clean. I just want to thank all of you for helping me out! I really do appreciate it.

Jason