1972 4HP Lightwin Slowly dying on top end

[monnewbie3]

Hey Everyone,

I have a 1972 4HP (4206S)Lightwin outboard.

Problem:
I've recently starting having a problem with the top end;
When full throttle for about 3-5 Minutes the engine slowly starts to die, slowly winding down until it dies.
On "slow" it trolls just fine, it only seems to die when wide open, this leads me to believe it could be a heat issue?
It is fine if left for an hour or 2, then it repeats the problem.
Engine seems a little hot to the touch... Stings right away, can't keep finger on for 2-3 seconds. Paint is not peeling away, and there are no visible signs of leaking from any gaskets.

Things I have done:
- New Plugs, properly gapped, they come out brown.
- Replaced rings, head gasket, rebuilt entire carb last season (ran great!).
- Ensured tight fit on fuel lines
- Running 45:1, since shes a little old
- Ran her a little rich just to make sure its not trying to seize on me
- Swapped the water pump impeller, ensured good steady stream out the back (done after first sign of problem).
- Spark appears to be good.

Thanks in advance for your help,

-M

 

[hidef]

Re: 1972 4HP Lightwin Slowly dying on top end

You should be running 24:1 for your fuel mix. Your engine uses bushings for the crank bottom end and on both ends of the con-rods. These engines do run very warm with anything over 163 degrees F. for the side of the cylinder being considered to hot. Have you tried top see if it Will keep running if you constantly squeeze the primer bulb to rule out a faulty fuel pump?

 

[monnewbie3]

Re: 1972 4HP Lightwin Slowly dying on top end

24:1? I did not know that... wow I'm quite off then.

Yes I tried to manually pump the primer bulb while on full top end, no difference. I recently put new lines and bulb on just in case.
Perhaps swapping my mixture would help? As it would cool it more.

 

[hidef]

Re: 1972 4HP Lightwin Slowly dying on top end

You might want check the carb just to make sure it isn't gummed up and that the engine is getting the fuel it needs.

 

[monnewbie3]

Re: 1972 4HP Lightwin Slowly dying on top end

Thanks for reply, I pulled the carb and checked to ensure fuel is flowing properly and blew out all the jets and passages. The carb was also rebuilt late last season.
The engine also runs fine on top end for about 5 minutes... then starts to die.. if I let it sit for about an hour it will work for another 5 minutes.
I think it could be heat related

 

[hidef]

Re: 1972 4HP Lightwin Slowly dying on top end

You might need to pull the lower unit again and make sure the water tube is inserted into the impeller housing correctly. My 4 doesn't spray water out the relief ports it is more like a spit. You can tell the engine is pumping but it won't soak you also when you had the power head off did you check to make sure the water passages were all clear?

 

[monnewbie3]

Re: 1972 4HP Lightwin Slowly dying on top end

Hey there, yes it's more like a "spit" with the rotation of the engine. Come out all 6 little holes.
I took very close care to ensure the water tube was inserted, also double checked it before tightening down (as I thought it could be a heat issue at the time).
All the water passages at the time seemed clear, the exhaust port needed to be cleaned, which was done.

Thanks again