05' Johnson 140 Wont start once warm

[scharote]

I have a 2005 Johnson 140 outboard (J140PX4SO) that doesn't get along with me... I bought it last year in April and did crank bearings because the previous owner ran her low on oil. I put it back together and it ran last year all year no issues other than always needing a little bit of throttle to start when cold.

Now I am dealing with the following:
When cold the motor will start the same as it always has, and run beautifully. It will idle fine and drives fine as long as I want, until I shut it off. When I go to start it again after it is warm I have my issue. It will crank crank crank until I stop, then backfire like a SOB through the exhaust, so hard it will actually blow my coolant return line off. If the motor DOES start, the weird part is it will only start when I stop cranking. In other words, I can crank for an extended period of time and as soon as I give up and let go of the key, it will fire (this is rare).

Things I have checked out so far:
-All cylinders have 160-180psi. Spark plugs look good.
-Water pump is new/working fine
-Engine Oil is clean and has no water in it.

I am thinking ignition system related or fuel pressure related but I don't really know where to start...

 

[scharote]

Bueller?

 

[iggyw1]

First off, let's consider what is making it backfire. A backfire is from timing set wrong, vacuum leak, running too rich, running too lean, blown exhaust manifold gasket, and a few other things, but these things would happen even when the engine is cold I would think. One thing that causes a backfire, and it could be happening after your engine has been running pretty much WOT for awhile is this: There is unburned fuel igniting in the intake or the exhaust manifold instead of the cylinder. One reason for this is that the motor is flooding with fuel.

Did you try to let the motor idle for 5-7 minutes or so before you shut it off when you get where you were going?? Try it. This could burn up any excess fuel in the motor if you do this. (This is not a remedy to cure the problem, but could point to what the problem is). Then shut the motor down & try to start it again. If the engine still will not start after you try this, open the throttle ALL THE WAY and crank the engine to start it. This is how you would start a flooded engine. Be prepared to cut the throttle way back AS SOON AS the engine starts. This will tell you if you have a flooded condition happening to your motor after you run it at higher RPM's on the lake before you shut it down.

If it starts by either idling the motor for awhile or cranking it with WOT, this would indicate a definate flooding condition going on. Your float might be sinking in the carb bowl or you could be running really rich all of a sudden from something vibrating out of wack and causing too much gas to flood into the motor.

I am not a mechanic, just some ideas I had to try to help you out. Hope this works out for you.