4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

[WaterView]

Hello and thanks in advance for any help?. Here is the story?

I have a 1980-81 Mercury 4HP 2 cylinder 2 stroke. I recently got this but it seems to have been well maintained with no corrosion at all.

It starts just fine and seems to run ok, except for a sketchy idle, for a few minutes.

After warming up though for 5 to minutes or so it starts to die out. After it starts to die out if I run it on half choke or so it will run for ever.

It has 105 lbs of compression in each cylinder when warm and I have cleaned the carburetor the best I can but there is no rebuild kit available so the cleaning is limited to what I can get at.

I also did take it apart and install a new water pump impeller and that seems have gone well, it is pumping a lot of water and running nice and cool.

My question is how do I make a diagnosis from here?

Thanks, Al

 

[Wingedwheel]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

It sounds like you might need to adjust your float.

 

[CharlieB]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

Once warmed and running, spray propane, butane, flamable carb cleaner, something at the carb base gasket, intake, crankcase parting lines, etc., watch and listen for any change in RPM, indicating air sucking into the motor, leaning the mixture and causing a need to additional fuel thru the carb.

Post model and serail, someone may have a lead on carb kits.

 

[WaterView]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

Thanks guys, Her serial number is 5927672 and best I can tell its model by searching online and looking at parts lists is 1004220. Great tip CharlieB thats the kind of diagnostic tools I need... I will try that tomorrow. I had to hammer out a new gasket that mates the exhaust sorta housing to the lower side of the cowling and power head could it be pulling air in through that? That gasket did not look too important seems to just keep exhaust gasses in the lower end.

 

[cr2k]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

Squeeze your primer bulb and see if that helps. Also make sure your fuel tank vent is open.

 

[aussieflash]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

Your going to have to crack her open to get at the needle n seat or floats.someone should have parts.

 

[WaterView]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

More info.... I have looked and the needle and seat and float they seem fine. I can get to those parts of the carb with no problem. I can't get to the locations under the little welch plugs. This motor also has a self containted fuel tank and a fuel pump but its pretty much gravity feed so no primer bulb. It does run for ever on half choke so it dosent seem to be completely running out of fuel. If I disconnect the fuel line going into the carb gas flows freely.

 

[Wingedwheel]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

Does the gas run freely because of the gravity feed? I think you still have a fuel pump which would be a small diaphram where the line feeds into the carb. You might need to replace that and like I said before, check your float setting while you have it apart.

 

[WaterView]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

Thanks, could you point me to instructions on how to set the float?

 

[bktheking]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

Good read on the gnat

http://www.themarinedoctor.com/cgi-bin/YaBB.pl?num=1173062165

You don't need a "kit" to pull the plugs, you need to match the plugs. Try a small engine shop, bet you they have plugs. I'll warn you now, the float height in this carb is a must, I had mine off twice until I got it to run right. It has to be bang on or the carb will leak gas. If it's not leaking gas then it's probably not the issue, it's more than likely dirty still.

 

[WaterView]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

Thanks bktheking, that link is just and excellent article on this motor... and your right how different could the welch plugs be.. I will read it carefully and see what I can do. I dont see any excess fuel in the carb when running so I will try a more complete carb cleaning first. Thanks again, Al

 

[WaterView]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

Hello, there is a tube that runs from the crankcase to the back of the carb area on the this motor. Can anyone tell me what its for and could it be causing my problem in anyway? Thanks..

 

[Wingedwheel]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

See if the hose you're referring to is item #5 in this diagram. http://www.boats.net/parts/search/M...INDER BLOCK AND CRANKCASE ASSEMBLY/parts.html

 

[WaterView]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

Hello,

I had to break away from this project for a bit but I am back on it now. The tube part I asked about seems to be much like a PVC valve on and older car motor and is just a check valve. I pulled the tube off and the check valve action is fine so I dont think thats my problem.

My next step is to try and clean the carb better.

Can anyone tell me the specific measurement for the float setting on the carb on this? What I can find on the Internet is conflicting from level with the casting when upside down, or 5/64 ~ 7/64, or 3/16.

My serial number is 5927672 and the markings on the carb I can find are Walbro Merc Carb 1-81 LMO 4.

Thanks, Al

 

[bktheking]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

I used a 3/16 drill bit between the float and the carb body, worked fine.

 

[WaterView]

Re: 4HP 1980 Mercury dies out after a few minutes and then only runs on half choke.

A final wrap up on this for the benefit of others.... Thanks everyone for your help!

I just got back from running this gal at the lake solid for two hours, running just perfect with a great top speed and purring at an idle.

I did a much more complete carb cleaning and float setting and she still died out after about 5 minutes only then running after that on half choke.

I backed up to what CharlieB suggested early about searching for an air leak. I did not try that at the time since it looked like she had never been apart before. Sure enough when I sprayed carb cleaner around the intake seams and the rpm's did change ever so slightly. I took the intake parts off and sealed them with some hardening permatex from the carb to the read holder and all seems just fine now.

So, thanks so much Carlie. bktheking you too seemed to be just right on for the float level setting, thank you.

I have gained a lot of knowledge on the this motor and if I can be of help to anyone else let me know.

Thanks again!