Mercruiser 120 Running on 2-cylinders - Flooding

[sidebojj]

I have a 1977 Mercruiser 120. I went to Summerize the boat and I can not get it running on all 4. At first I could not get it running at all, but after a while I got it to fire but it is only running on #1 and #4. (I pulled the plug wires while running) I checked over all the electrical stuff first, timing, point gap, cleaned points, tried different rotor, etc. I have spark in all four cylinders, and lots of fuel. The plugs were soaked in all 4 when is was not running and are soaked in #2 and #3 now. Boat ran fine when put away in the fall. So I figured I had a stuck float, but I took the top of the carb off and everything seemed fine. Still is only running on 2. I rebuilt the carb last year.

The inside of the carb is soaked, along with #2 and #3 plugs when the boat is running. It will not idle (spits out the carb and dies) Runs fairly smooth at apx 2000 rpm but will backfire if accelerated quickly. My opinion is that there is something in the carb (other then the float) which is overfueling the motor, and raw fuel is running down the intake into #2 & #3 flooding them out and not letting them fire.

Has anyone had this problem? What else could it be other then the float?

Edit: have 105-115 psi compression in all holes, and the valvetrain looks good.

 

[Silvertip]

Re: Mercruiser 120 Running on 2-cylinders - Flooding

You have a carb issue and the float has either sunk or the needle and seat are not closing when the float rises (jambed due to the float dropping to the bottom during storage after the fuel evaporated from the carb) so fuel level rises and floods the middle two cylinders which are closest to the carb. Fix it with a rebuild kit and replace the float and make sure you get the inlet needle installed properly. Did you at least try replacing the plugs?

 

[sidebojj]

Re: Mercruiser 120 Running on 2-cylinders - Flooding

I have changed the plugs, did not help. I had 10 min to work on it yesterday while the yard roller was filling so I pulled the top of the carb off and the float did not seem to have any fuel in it but I will double check. I also blew into the fuel inlet with the float up to make sure the needle was sealing on the seat and it was. I thought the float level seemed high so I moved it down a little but that did not help either. The bowl was only 1/3 full of fuel but I do not know how much evaporated since the last time I worked on it. Is there anything else besides the float/ needle that will flood these rochester carbs?

Edit: I rebuilt the carb last year in July. I will do it again if it will help but I am not convinced yet that it will fix the prob. I did notice the gasket between the cover and the body of the carb was torn but I did not see how that would cause the flooding. (I will be getting a new gasket if I do not have one)

 

[Maclin]

Re: Mercruiser 120 Running on 2-cylinders - Flooding

There could be some plugs in the base plate that are leaking. I have seen that in Rochester Quadrajets and Carter Thermoquads. They are plugs that are doped in and that can start leaking, gasoline goes right into the intake manifold. I do not have experience with the Rochester 2bbl so I do not know if that applies to your case or not.