Excessive Gas Starts Fire 86' 75 HP merc

[Myke48]

Outboard was running good,got it starting good and no bogging,,,now I have a new problem,,,,I leave my motor tilted up with a transom saver bar,,,I disconnect the gas from the tank quick coupler when not in use and when I trailer it to the ramp.
When I start the motor this is my procedure,,,I let the tilt all the way down,,,I squeeze the bulb about 3 to 7 times,till its hard,,sometimes only 3 times then sometimes 7 to 8..when i feel the bulb hard I notice that there is fuel rainbowing the water,,,then when I start it ,it causes a flash fire,,,I can see the flames coming out of the bottom part of the cowling I then use the extinguisher to put it out,, and then take the boat home,,hose the powder off the cowling from the extinguisher and then start it up no problem..no fire.
There is no backfire or unusual noise except a "Poof" noise..the fire has not damaged anything ,,no burnt or melted wires,can not even tell there was a fire..,,the motor is a 1986 75HP merc with "C" carbs.I feel it might be a stuck float ,I am ready to take the carbs off and clean them ,,but would like to know what else could cause this fire problem.Thanks in advance for your wisdom here on the forums

 

[CharlieB]

Re: Excessive Gas Starts Fire 86' 75 HP merc

A leaking carb, fuel line, or poor connection at any fitting , any or all of these will end up with fuel in the water. Exhaust is accompanied with flame, and fuel in the immediate vicinity of the exhaust will ignite.

Fire within or around a boat is no joke, that's why it is critical to be aware of the condition of your fuel system and it the first sign of leakage to get it dealt with immediately.

If the motor is trimmed down all the way carb flooding may be hidden, running down the carb throat into the intake. Trim the motor dead level to 'slightly' positive, uncover/remove the airbox and carefully look down the carb throats while pumping the primer. Squeeze and hold pressure on the bulb while you look down each throat as well as inspect ALL fuel lines and fittings for any leakage, however slight. Repair as necessary.

 

[j_martin]

Re: Excessive Gas Starts Fire 86' 75 HP merc

If you're one of those guys with a painful handshake, it's pretty easy to overcome the needle valves in a normal carb by squeezing the bulb.

When it gets firm, don't squeeze real hard to be sure. It's primed already. As you squeeze prime the carbs, when they fill up, you'll feel a definite resistance in the bulb. That's good enough. You shouldn't be generating a rainbow for sure. If you do, you're in danger, as you found out.

hope it helps
John

 

[Myke48]

Re: Excessive Gas Starts Fire 86' 75 HP merc

I found out where the leak is from,,,,if I just squeeze the bulb normal/easy gas pours out of the vent valve on the top carb,,it is the valve on the port side opposite the lean / rich adjustment ,,,I got a gasket set and cleaned the carbs installed new gaskets and I still have the same problem,,,when I squeeze the primer bulb gas pours out of the vent valve.The float valve seemed sticky compared to the bottom carb,,bottom carb travelled smoothly up and down,,,top valve seemed to stick. Any suggestions as to what to do next,,,I am thinking putting a new float valve in,,,I just need some direction heer,,thanks guys,,,,Mike

 

[Myke48]

Re: Excessive Gas Starts Fire 86' 75 HP merc

Float valve = I mean Needle Valve

 

[j_martin]

Re: Excessive Gas Starts Fire 86' 75 HP merc

Make sure the float is OK, not gas logged (if foam) or leaking (if shell brass or plastic). Then install a new needle and seat assy.

There's a remote possibility that you have a casting failure. You should be able to see that as you clean it out and blow it out with compressed air.

hope it helps
John