Mariner 3.5 four stroke...what on earth is wrong with it?!!!

[dustywings]

I have a Mariner 3.5hp four stroke outboard on my tender which has been a great engine for years and has had relatively little use. Towards the end of last season it developed a cough when opening her up and would eventually die but always restart. It will run out of gear perfectly when I flush it out after use in a tank of water, the problem only occurs under load. My initial thought was fuel so I changed the fuel, cleaned the tank, checked the lines and shut off valve (there is no filter) and blew the carb through with an air line but to no avail. On talking to my local dealer they suggested it would be the carb so I pulled it apart entirely, soaked it in carb cleaner, blew everything through and reassembled but still no change. Having convinced myself that it was not the fuel I have bitten the bullet and fitted a new igniter (which wasn’t cheap!) but as you have probably guessed still no change. I am totally stumped, has anyone had a similar experience and might be able to shed some light on where to direct my efforts?

Thanks in anticipation!

 

[oGaryo]

I have a Mariner 3.5hp four stroke outboard on my tender which has been a great engine for years and has had relatively little use. Towards the end of last season it developed a cough when opening her up and would eventually die but always restart. It will run out of gear perfectly when I flush it out after use in a tank of water, the problem only occurs under load. My initial thought was fuel so I changed the fuel, cleaned the tank, checked the lines and shut off valve (there is no filter) and blew the carb through with an air line but to no avail. On talking to my local dealer they suggested it would be the carb so I pulled it apart entirely, soaked it in carb cleaner, blew everything through and reassembled but still no change. Having convinced myself that it was not the fuel I have bitten the bullet and fitted a new igniter (which wasn’t cheap!) but as you have probably guessed still no change. I am totally stumped, has anyone had a similar experience and might be able to shed some light on where to direct my efforts?

Thanks in anticipation!

Hi, sorry to hear of your troubles. when was the last time you cleared out the waterways (salt deposits), overheating springs to mind. maybe worth a look even if it's still spitting from the pee hole

 

[dustywings]

Thaks for the reply Gary it was flowing fine last year and over the winter as part of the service I changed the impeller so I think it should be fine plus it happens immediately when it hasnt even warmed up.

 

[crazy4557]

I had a similar problem with my Tohatsu 4hp 2 stroke. Was a complete arse! Ran perfectly for a few minutes under load then died. Sounded like fuel starvation. Always restarted immediately and would rev perfectly without load but would then struggle to rev under load for a while then cut out again. Back to the dealer three times and each time the carb and fuel system was cleaned more and more thoroughly...how clean can you get a carb for god's sake!
In the end they fitted a brand new carburetor and it fixed the problem but they still don't know what the problem was with the original carb.
The outboard as only bought in 2008 brand new (old stock).

So OP maybe a new carb might be the only way to go....

 

[dustywings]

I have contemplated that but it always seemed a bit extreme although Dave Crawfords suggested the same thing. If nobody has any other ideas I may have to do that as it seems it may be the only solution.

 

[[2068]]

On my 5hp two stroke, it was the needle valve that regulates the fuel level in the float chamber that was sticky.
Yours might be different, but focussing on this bit might help.
It would fit with "relatively little use" as it can get gummed up.

 

[dustywings]

Thanks FP for the suggestion but I removed the valve and cleaned thoroughly, it looks perfect.

 

[crazy4557]

I have contemplated that but it always seemed a bit extreme although Dave Crawfords suggested the same thing. If nobody has any other ideas I may have to do that as it seems it may be the only solution.

It was Dave Crawford's that fixed mine...eventually. They were very perplexed but also patient and helpful.

 

[Chris_d]

Is the tank breather ok? run without the cap and see if it still does it.

 

[dustywings]

Thanks again for the suggestion but I am afraid yes I have tried that.

 

[dustywings]

I have just had an interesting conversation with a different dealer who suggested cleaning the carb out....yawn! But also that after 15 hours running these engines need their mixture resetting, the adjuster is apparently sealed under a cap to comply with the US emissions. Does that sound reasonable?

 

[VicS]

I have just had an interesting conversation with a different dealer who suggested cleaning the carb out....yawn! But also that after 15 hours running these engines need their mixture resetting, the adjuster is apparently sealed under a cap to comply with the US emissions. Does that sound reasonable?

Whether or not it is reasonable for a sealed mixture setting to require re-adjustment after 15 hours I'm not sure but it does suggest that there is a little orifice there which you have not been able to clean .

 

[dustywings]

Yes I agree the question is if its possible to do it as the professionals don't seem able to and instead choose to fit a new carb. I will have yet another go and see if I can make any progress.

Thanks to everyone for comments so far.