Fuel pump

[Tony Brooks]

What colour? If its whitish its probably vaporised fuel in the exhaust evaporating away. although you probably did not inject enough fuel to start you probably injected some that did not burn so is not soaked into carbon in the exhaust.

 

If it black then as long as you have not messed with the pump timing I have no idea, might be idle damper adjustment but can't see how. If its at high speed while boating probably overloading because of oversized prop of trying to go too fast/leaves around the prop.