4.3 Mercruiser rough running when warm.

[jet pilot]

Well. There is no way to make this short. I want to give the experts here all the information. 1992 4.3l. Last summer the boat ran great right up until the fall when it was winterized. I winterized it the same way as the last 4 years (using the manual). I must have forgotton something because this year when I went to start it, hydro-lock!. Puled the spark plugs out and water came out of 4 of the 6 cylinders. Assuming the exhaust manifolds were cracked, I had them xrayed. They were good. I ordered new heads and put them on after clearing the water out of the cylinders. I used marine head gaskets, intake gaskets and exhaust gaskets. I have extensive back ground in mechanics so I know my way around an engine. When I put the distributer back in, I lined up my index mark on the housing with the mark I made on the intake and then lined to rotor up with the mark on the housing (then engine was undisturbed to this point. I set the rocker arms according to the manual..#1 cylinder on tdc of compression stroke adjust certain valves, then roll the engine to TDC of #4 and adjust remainder of the valves. Put it all back together and started it up. It would only run at 3000rpm. Anything less and it would die and run rough. I checked the plug wires to make sure they were correct. Thinking I did something wrong with the valves, I did the valves again. Same thing. Put it back together and same issue. I took the carb off and tookit apart. I found aw hole bumch of white gunk in the bottom of the bowl. I soaked it and put in a mercruiser carb kit and fired it up. Ran perfect for about 30 seconds. Then started running rough again. Thinking that there was water in the fuel tank, I drained the tank and put in 5 gallons of fresh. Same thing. I am at my end of the rope. I should also mention that there is new cap, rotor, plugs and the oil was flushed and drained and a new filter and oil installed before I started it. No water in the oil right now.

I decided to post here first before bringing it to the stealership! Any help is appreciated!!

 

[jet pilot]

I forgot to add that a compresion test showed 140-155 between all cylinders.

 

[Bondo]

I took the carb off and tookit apart. I found aw hole bumch of white gunk in the bottom of the bowl. I soaked it and put in a mercruiser carb kit and fired it up. Ran perfect for about 30 seconds. Then started running rough again. Thinking that there was water in the fuel tank, I drained the tank and put in 5 gallons of fresh.

Ayuh,.... Welcome Aboard,.... Did ya change the fuel filter at the same time,..??

Does it have the canister type filter,..??
If not, add 1 ahead of the fuel pump,...

Did ya examine the Contents of the old 1,..??

I'm guessin' this is where the problem lies,... a lack of fuel,... plugged idle circuit in the carb,....

 

[jet pilot]

The only fuel filter that is there is the one in the carb. no water filter. Carb was gone through, cleaned with a kit installed. Idle circuit seemed clear..might take it back apart and see. After writing this post I went out and puts around more..if I manipulate the choke by hand, I can get it to idle down, but the choke is almost closed to do so. So I do believe it is in the fuel system..

 

[Bondo]

The only fuel filter that is there is the one in the carb.

Ayuh,.... I believe you'll find another inside the fuel pump, like on a 3.0l motor,...

I'd still add a canister style 'tween the tank, 'n fuel pump,....

 

[jet pilot]

right you are. Right on top the fuel pump. I will be adding a water seperator after this!