90's 4hp 2stroke damage from overheating

[blackrandomapple]

Hello everyone.
It's been a long long time since posting here.

I have a problem.
I have a 90s 4hp 2 stroke outboard that I use on a little rib with my 3yr old son on the canal.
Unfortunately, I failed to notice that the motor wasn't pumping water last time we went out and I have over heated the motor and I only realised as the motor wouldn't run at normal speed, that's when I noticed the smell of a hot engine.

I only ran it for a max of 5 mins but I believe some damage has been done.

I have since replaced the impeller as this was the problem (the impeller had completely failed)

Anyhoo, I have run the engine in the wheelie bin but it does seem that some damage has been done.

My question is: what time will be damaged by overheating?
It will idle and run ok when not in gear.
When in either forward or reverse it will idle and run at low rpm.
When under load the motor will bog down or simply lose power and cut out.
Motor starts with no issues when either warm or cold.

Although it's a 90s motor it has had very little use and always maintained well, untill my mistake this time.
There aren't many hours on it at all, to look at you'd think it was brand new

I need to resolve this asap as I have my son with me next week and I had planned on using it.

Any help will be very much appreciated.

James

 

[Channel Sailor]

from what you have observed it does not sound like overheating damage. I reckon overheating damage would be in the cylinder such as rings damaged the barrel, piston expands due to heat in the cylinder and damaged the cylinder, head gasket or head alloy damaged, hole in the top of the piston. All of these would mean the engine would not even start. Bogging down under load sounds like a fuelling problem, such as the tank air vent blocked.

 

[blackrandomapple]

Hello and thankyou for your reply.

I too wouldn't have thought that I had caused much damage but the week previous to this the motor was running absolutely perfectly.

I will double check vents as suggested Tomo but I am almost certain everything will be as it should.

It's only since the overheating that the engine has ever failed to run properly

 

[VicS]

If it starts easily and idles properly it seems unlikely that any real damage has been done but it would be sensible to carry out a compression test .

A fuel flow or carb problem seems likely but have you tried a new sparkplug?

BTW what engine are we talking about.

 

[blackrandomapple]

Hi.

I've not yet looked into it in detail and haven't checked the plug etc

It's a 90s 2stroke hp mercury outboard

 

[Channel Sailor]

What would I do. Take the plug(s) out and turn the engine over on the pull cord to check for a nice compression, no horrible scraping noises and a smooth operation. Put the plugs back in, start the engine and listen for a loud slapping noise from the piston. Inspect the fuel system carefully including : fuel filter above the tap in the fuel tank, inside the fuel tank for gummy deposits, take the float bowl off and clean inspect everything inside. Including the main jet. Blow /clean the tank to carb fuel hose. Check carb is correctly located on the engine with no obvious air leaks. Check the choke lever works the closure opening and closing plate. Check the throttle opens carb piston and the main jet needle can been seen. Dispose of the fuel you have been using and mix up some fresh petrol/oil mix for testing. Reassemble but pull the fuel hose off the float bowl and put the end into a container, turn on the tap and check fuel flows freely. Careful to avoid spillages. Switch off tap and Put the hose back on the carb.

Start the engine on choke, warm it a little and then back off the choke, test. If still playing up then next take the cylinder head off to inspect the barrel and piston top. Decoke the head while it is off. Refit with a new gasket.

Next could be the crankshaft oil seals are damaged, so air is leaking in. I am not sure if there is a way to test for that problem.

I would say gummed up fuel filter is my favourite, then gummed up carb. Plus cylinder/rings damage as well, but not enough to cause a serious problem immediately.

 

[Channel Sailor]

Oh, yes. Change the plug as well.

 

[blackrandomapple]

Oh, yes. Change the plug as well.

Thankyou. Although I am not stranger to engines it's always good to have someone prompt and guide me.

I will have another read of your post Tomo afternoon whilst I have the engine Infront of me.

Thankyou

 

[blackrandomapple]

Ok guys, before I go taking apart the motor I thought I'd record a video for you guys to watch.

My only hang up here is that a week previous to the impeller failing the motor was running like a dream therefore I can't see what could have changed since it was last used.

YouTube Link CLICK HERE

I will of course be taking the necessary steps to resolve the issue but before I do so I'd like your thoughts on the video please.

Thanks again

James

 

[Dellquay13]

A quick check to confirm a fuel issue would to start it then a little squirt of some easystart or fuel from a plant mister bottle down the carb air intake. If it roars off for a few seconds it’s probably a fuel problem

 

[Channel Sailor]

Sounds like a fuel problem to me. Float bowl not refilling fast enough.