Yamaha 4HP 2 stroke 1994 dies when accelerating

[Yamahama's]

Hi,

I just bought a Yamaha 4 hp 2 stroke longshaft from 1994. It starts right away, but when i accelerate the engine just dies until I put it in idle.
When I put in in gear, the same thing happens. If i play a little bit with the choke (opening and closing quite fast), the engine appears to work just fine when throttling.
This model only has a built in tank, with a fuel tap next to the killswitch.
Servicing outboards is new for me, but i'm very keen to learn. But before I order new parts (which is quite costly), i would like to know your thoughts on this.
I already noticed that some fuel leaks from the bottom of the fuel tank, where the tap opens and closes the access to the tank, but i think that is not the main thing that causes this problem.

Any thoughts on this?

Thanks in advance!

 

[VicS]

I'd suspect that the carb may need a clean

but check the fuel flow to the carb. I think there is a filter in the tank that's part of the fuel tap assembly ... check that

The carb incorporates a pump which might be sucking air in through the little leak you have especially if the filter is restricted ... I'd fix that

Tank vent opening and clear?

Also check the spark... it should be able to jump an air gap of 1/4" ......... and always try a new plug. Otherwise don't buy parts until you have diagnosed the problem or you'll spend a shed load of beer tokens on parts you don't need

Parts lists and exploded diagrams at 1994 Yamaha 4MLHS Outboard Motor Parts [4HP] | Boats.net

Should be covered by this manual http://www.boatinfo.no/lib/yamaha/manuals/1984-1996yamaha.html#/0

 

[QBhoy]

Clean the carb. Worst case it’s the accelerator pump passing. Very typical of what you describe.

 

[Yamahama's]

Sorry for the late reply. Cleaning the carburator was indeed the solution. Took it apart, put some carb cleaner in it and the problem was gone with the wind! Now working on a 3hp Yamaha Malta... Absolutely no cooling water was coming out either from the telltale or from the lower unit. The impeller was almost completely gone! Waiting for the replacement to arrive from the shop, could take a few days. Anyways, thank you both for the advice. This has indeed saved me some beer tokens!