Fuel in my airbox??

[MichaelScott87]

I have a 1996 Mercury 200hp 2.5L Offshore motor (carb). I'm having a problem with the motor not running right everytime I go out for the 1st 5-20 minutes. It will only run about 8 mph full throttle and then out of knowwhere it will slowly increase rpms and speed. I will not have a problem with it the rest of the day. Someone mentioned to me it could be fuel getting into my airbox since I trailer by boat for an 1 1/2 hours to get to the ramp with the motor up obviously. I didn't pay much mind to his comment until this weekend I left my boat at the marina with the motor down overnight. I put it in the water the next morning and it ran great right off the bat. Does this theory sound right. I started my boat with the hose on it and ran it for a while in the yard and tilted the motor up and will leave it overnight. In the morning I'm gonna take the airbox off and check it out. I'm just wanting a few opinions.

 

[CharlieB]

Re: Fuel in my airbox??

Most carbs flood an amount when tilted full up in the trailer position. Older models let the excess fuel drain out on the ground , EPA put an end to that, now airboxes are installed with a reservoir to hold the fuel and a recirc hose to pull it in and burn it off once the engine is started.

How old and what condition are your spark plugs?

Marginal plugs may fuel foul from the richened mixture of that first start after a full tilt, after running for a while the plugs burn clean enough that the motor performs acceptably, until you full tilt it again.

Even one or two partially fouled plugs could cause the motor to not perform until cleared.

 

[MichaelScott87]

Re: Fuel in my airbox??

That is whats going on but I change plugs and it just refouls them because of the excess fuel bogging it down. How can I stop this. If I disconnect the fuel line while running in my yard flushing the motor will that cause harm? I have to put an end to this as its driving me nuts!

 

[CharlieB]

Re: Fuel in my airbox??

If the idle mixture on one or more cyls is a bit too rich, then adding the additional fuel from the airbox you would have this problem.

When was the last time your carbs were thoroughly clean? A float just a bit too high, too rich an idle mixture screw, or a dirty idle air bleed, any or all could contribute to your problem.

The airbox drain hose should have a one-way restrictor valve where it connects to the engine which limits the rate of fuel being added to the motor. This should not be causing a problem unless someone replaced that fitting or you have a carb issue.

Yes, you may elect to disconnect the fuel line and run the carbs low/out of fuel prior to trailering, but that is simply treating the symptoms, not the root cause of your problem.