Need to know year of this outboard

The serial number relates to either DT65ESX or DT65ELX and the year of manufacture is 1981

Frans, Check the attached links,instruction and guides, Good luck
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suzuki 100 hp outboard specifications Google Search
Suzuki
https://www.tradebit.com/filedetail.php/142965517-suzuki-outboard-service-manual-df90-100-115

if you are happy with current propeller then take prop off lower unit and look on the backside of the prop..it should show size and pitch close to center

did you remove the pin below the carbs for the gear rod ?

yes. OR you have an air leak in the fuel system. Easy way to tell is with a clear fuel line between the fuel pump and the carb. If you see bubbles, you are looking at a new fuel line connector or aire leak at the fuel pump. If you pump up pressure with out the motor running A fault may leak gas.