What is engine flooding?

[steam_mill]

When is an engine flooded?<br /><br />My merc 7.5 will not start after sitting for about 30 minutes.<br /><br />Read it might be my carb or fuel bulb.<br /><br />It may be flooded.<br /><br />What is an engine flooded.<br /><br />I thought that with the float valve, no more fuel would get into the carb.<br /><br />Therefore extra fuel could not get to motor and it would never flood.<br /><br />Now, I know I'm wrong but would appreciate an explanation of flooding.<br /><br />Tx.<br /><br />Joe

 

[Solittle]

Re: What is engine flooding?

Joe - For the fuel - air mixture in a cylinder to fire it needs to have the correct ratio of fuel to air. Too much fuel is called flooding. With a standard carb you can clear it sometimes by opening the throttle wide open. This will allow more air in.

 

[Silvertip]

Re: What is engine flooding?

The float valve shuts off the flow of fuel to the bowl (resevoir) in the carb. The level in the bowl must be at a specific setting for proper operation. Even though the float shuts off the fuel when the bowl is full, the engine still draws its fuel from the bowl. A bad inlet needle and seat will not allow fuel to be shut off resulting in flooding. Over-use of the choke will flood the engine. Improper starting procedures can flood the engine. Flooding means too much fuel is reaching the cylinders.

 

[Paul Moir]

Re: What is engine flooding?

I though flooding was essentially wet fouling of the spark plug. That is to say, the spark plug has been shorted out by excessive fuel. By giving it a few pulls or cranks with the throttle wide opened, you would dry out the plugs enough for them to fire since with the throttle wide open not enough velocity/vaccum is created in the carb to draw any additional fuel.<br />Just being a little rich seems to me to cause four-stroking, rough running, and excessive smoke. Run too rich and you're flooding/fouling.<br />I think I've heard a leaking needle and seat called 'carb flooding'. Seems to be an acurate description to me.

 

[Silvertip]

Re: What is engine flooding?

Wet fouling is indeed flooding. However, if the engine doesn't start because its flooded, it really doesn't matter how it happened. It has too much fuel and not enough air. Bad carb, incorrect starting procedure, poor state of tune, weak spark, all can cause flooding. Ever heard the story about a full fuel tank won't explode but an empty or partially empty one will? Fuel with no air won't burn. A little bit of fuel with proper amount of air goes "BANG". Lots of shade tree mechanics attempting to repair gas tanks learned that lesson the hard way.