Engine looses power

I have an old 6hp Johnson. The

I have an old 6hp Johnson. The engine starts great and when it starts and I give full throttle it works great but after about 5-6 seconds it slowly starts to loose power till about half of its power in the first place. The spark plugs are pretty oily and wet so I think thats it but I am not sure especially because the ignition is set as in the manual?
SO any idea what could it be

"First always worth checking/

"First always worth checking/cleaning/adjusting or replacing plugs. You dont say which year so cannot advise on currently recommended type.
Also worth checking the sparks, the condition of the coils and the HT leads and if it is pre 1977 the points.

The wet oily plugs may be the result of not firing properly but they may be due to the carb float not controlling the fuel level. Stuck, defective or incorrectly adjusted float or the needle valve not closing properly.

If you prime the carb with the bulb, start and immediately disconnect the fuel line will it run for longer? If so it points to the float or needle valve.

Choke opening fully when the control returned to its normal position?

Carb mixture settings correct?

Always quote the year and/or model number when asking questions."

"ok the engine is 1969 so real

"ok the engine is 1969 so really old.The spark plugs are really greasy but they don't look worn out but i think its wort changing.

the points look a bit worn out and the coils aren't much better but I cant find the parts here or they are extremely expensive (one coil 70 $) so I wont buy it if not really necessary. And when i disconnect the plug it has a really good spark on the upper cylinder and not so good on the lower but acceptable.

Now the carb was cleaned so it hasn't a problem with that.I have a problem with the needle valve (it only has the upper one) that it unscrews its self ,could that be it? And how do I adjust the mixture I am not sure?"