1979 mercury 900 90 hp dies under load

[smokeyblaze]

She runs fine when out of the water on the muffs but when shes in the lake she will hardly take any throttle before it sputters and cuts off unless i back off the throttle almost to idle speed.

 

[Laddies]

Re: 1979 mercury 900 90 hp dies under load

You have dirty high speed jets clean the carbs.

 

[smokeyblaze]

Re: 1979 mercury 900 90 hp dies under load

I found that pumping the primer bulb helps get me up to about 30mph. Could it be my fuel pump?

 

[Laddies]

Re: 1979 mercury 900 90 hp dies under load

I doubt it but it des sound like the whole fuel system is varnished up and needs to be cleaned. If you continue to run it lean you will damage the engine.

 

[smokeyblaze]

Re: 1979 mercury 900 90 hp dies under load

Whats the best way to use sea foam on my outboard?

 

[mthieme]

Re: 1979 mercury 900 90 hp dies under load

Sounds like it could be the fuel pump to me. This is easier and cheaper than starting with the carbs.
Has she been sitting for a while?

 

[smokeyblaze]

Re: 1979 mercury 900 90 hp dies under load

She sat for about 8 months When I was reflooring it and replacing the transom and carpet. I'm just scared that if I take the carbs off that they won't get put back on properly.

 

[mthieme]

Re: 1979 mercury 900 90 hp dies under load

8 months isn't too hateful.
If you haven't done carbs before, you might want to recruit some help. Getting them on and off isn't too hateful. They aren't necessarily hard and the crew can walk you through any problems you run into. The fun will start after the rebuilds.

 

[smokeyblaze]

Re: 1979 mercury 900 90 hp dies under load

So should I check into the fuel pump before I attempt to take the carbs out or Should I try to use some seafoam ?

 

[Laddies]

Re: 1979 mercury 900 90 hp dies under load

In 45 years I have never used seafoam, there are many other products out there that are designed to clean carbs. After all about 90% of seafoam is alcohol so why not just burn ethanol, Oh thats right it cut the varnish loose and it plugs the jets. keep it up and you will burn a piston.

 

[Chris1956]

Re: 1979 mercury 900 90 hp dies under load

Smoky, The symptoms you have described could be attributed to weak fuel pump, incorrect idle mixture setting or clogged high speed jets. I would rebuild the fuel pump first, since it is the easiest. If that doesn't fix it (I will bet it wont), you will need to get into the carbs. The high speed jets can be cleaned by removing the brass hex plug in the base of the carb bowls. You will not be able to clean the idle circuit and idle restrictor w/o disassembling the carbs, however. Adjusting the carbs after the rebuild is a bit tricky since they need to be lean enough to idle well, yet rich enough to accelerate.

 

[smokeyblaze]

Re: 1979 mercury 900 90 hp dies under load

Upon inspection today I found a hairline crack in one of my fuel lines , it's not very noticable but its definatly there , could this among everything else mentioned be the cause of my problem? Where can I find a replacement?

 

[mthieme]

Re: 1979 mercury 900 90 hp dies under load

Yes it can.
Fuel line can be had at your local marine store.

 

[smokeyblaze]

Re: 1979 mercury 900 90 hp dies under load

Theres really not any local marine stores in my area , I get all of my parts online. Anyone got a link? thanks mth

 

[mthieme]

Re: 1979 mercury 900 90 hp dies under load

www.iboats.com

 

[smokeyblaze]

Re: 1979 mercury 900 90 hp dies under load

All I see is fuel lines from the tank to the motor , I'll keep looking though

 

[mthieme]

Re: 1979 mercury 900 90 hp dies under load

This'll get you a little closer.
It looks like you have a choice of 10' or a 50' roll.


http://www.iboats.com/Fuel_Lines_Ho...2947288--**********.590379316--view_id.238199

 

[smokeyblaze]

Re: 1979 mercury 900 90 hp dies under load

I also noticed when i trimmed the motor up all 3 carbs were leaking gas. what causes this? where is the needle that is supposed to move with the throttle located?

 

[mthieme]

Re: 1979 mercury 900 90 hp dies under load

Inside the carb. Do you see this coming out of hte cowl, are you seeing with the cowl off? are you seeing this with the airbox off? Are we talking just a drop or two. Or are we talking a small stream?

 

[Chris1956]

Re: 1979 mercury 900 90 hp dies under load

It is normal for the carbs to drip gas when the motor is tilted up.

Those motors do not have airboxes, only plastic gratings over the carbs.

You can get new fuel lines at any automotive store. 5/16" or 3/8" is the ID size for the ones between the carbs and fuel pump. Also check the balance hoses on the crankcase cover between the carbs, as well as the real thin hose that runs from the bottom main bearing and the top main bearing. Replace as necessary.