I have a 97 Yamaha gp1200 and it floods all three cylinders when shut off. It runs fine if I clean all the gas out first but when turned off it vapor locks all 3 every time. If I let the return line run free into a gas can it will start again and everything is fine. It seems as if it’s building pressure in the gas tank. Any solutions? Please and thank you.

Fuel may be boiling in the line or bowl and causing a vapor lock situation .

Vapor lock only happens when the vehicle is hot. Flooding at start up, you smell gas. If it is over fueling threw the carb/throttle, then you will see lots of black smoke out of the tail pipe when running.

Check the oil, the low oil sensor will disable the ignition if more than a quart low. When on vacation (touring) , check oil often. Pumping the gas pedal with modern fuel injection will not flood the engine, it does not work that way.

Define flooding.

1. Black smoke out of the tail pipe?
   

If the fuel return line is plugged,it will flood.If the fuel pressure regulator has lost its vacuum signal ,it will flood.

If there is a large vacuum leak,the O2 will see a lean condition and cause the rich condition.gas mileage will suck,big time.

This "flooding" happens when the engine is cold? ONLY?
Be sure the air filter is not clogged and the PCV is not plugged up solid.
Also,there are a few tubes from the valve cover that vents oil vapors into the air filter housing.

During this flood mode,hold the pedal to the floor and shut the engine OFF-it should NOT keep running.(Leaky injectors)...

Do this when engine is hot and cold.

.When the injectors leak they flood the engine and holding pedal to the floor or waiting hours for fuel to dissipate. See if you have spark and fuel when it wont run. If there is no spark check the electronic control module under the cap

have your evaporative emission control system check.sound like you have purge valve solenoid not working or vent valve control solenoid.have it scan.to see which component not working..reason your gas tank expanding. your fuel vapor building up pressure.your purge valve and vent valve open allowing gas vapor from charcoil canister. to be burn in the intake manifold to be burn in combustion chamber.

You are on the right path. You gave away the answer when you said you can dry the plugs and then it will start and run for a few seconds before flooding out again.

To solve the problem (there seem to be two of them) do the following:

You need to stop fuel from entering the engine, either disconnect the fuel line from the tank to the fuel pump or route the output from the fuel pump to a gas can or back to the tank, just don't let it get to the carb.

Pull the coil wire, pull the plugs and spin the motor over so it can get dried out.
Pulling the coil wire should help reduce the risk of the fuel being blown from the cylinders from somehow getting ignited. BE CAREFULL!!!

Now dry the plugs and put them back in, plug in the coil wire and fire it up. Based on what you have said it sounds like it will probably start up (if only for a second or three). Now pour two or three teaspoons of gasoline into the carb and start it again.

If it starts and then dies that is a good thing. Do the two or three teaspoons and start it two or three times. This will heat up the compression chambers a little and help to dry them out a little better.

Now, at this point it runs fine (well as fine a 2 or 3 teaspoons will run it) as long as it has fuel, air and spark.

Hook up the fuel line again and start it up. One of two things will take place.

1. All is well! Great, it was just REALLY flooded.

2. It runs for about 10 seconds before becoming flooded again.... ****, it sounds like your "new" carb is flooding the engine. Find out how!

Good luck. I have used this "fix" a few times over the years. Normally the engine is REALLY, REALLY, REALLY flooded. Usually because the original problem happened on a hot summer day and the float stuck when the engine was shut off. The heat of the engine boiled the gasoline which in turn flooded the engine. The float stayed stuck when they came back to start it and TA DA.

Several times a little tap on the side of the carb "cured" the problem and a fuel additive was used to clean up the sticky float issue.

In one instance the 4 banger was so flooded we had to snake a hose into the cylinders and **** the fuel out. We must have sucked a quart of fuel out of that little '80 Mustang. We still ended up draining the oil (it smelled like it was full of fuel too) and we spun it over until it quit spraying gasoline all over. Man was that a mess!!!

you have one our two problems the coolant temp sensor has failed our the fuel pressuer regulator has failed. the regulator is controlled by vacuumn and is in the fuel rail remove the vacuumn line if any fuel runs out it has failed with the line removed try cranking the mtr over and see if it floods good luck kdc744

Have you tried unhooking battery for several minutes. This should allow the computer to re-boot.

semms to be like some of the vapor lines coming from thank to engine might be flooding your engine,
but also locate the fuel pressure regulator at the engine compartment and unplud the vacium hose, if you see any fuel coming out from fuel pressure regulator, or if the vacium hose smeel like fuel, then the regulator is not good.