4.3 Mercruiser starts, then dies.

I have a 2000, plugs and carburator 4.3 chevy in a Bayliner. It will start and run for about 10 seconds, then seems to run out of fuel. If the switch is turned off and then to starter again, it will start, run good for about 10 seconds and then dies. Checked the fuel pump, carburator, filters, etc. The problem is that it is not consistent, so the mechanic can't find the problem. I have lots of bucks in it so far trying to find the answer. Any ideas?

Could be several things, but first thing I would do is hook up a fuel pressure gauge to see if you are loosing pressure after start up. The fuel pump is energized when the ignition switch is in the start position (while cranking). Once the key is released and the key is in the run position, the fuel pump gets it’s power through an oil switch. In other words, the engine has to have oil pressure for the fuel pump circuit to be completed. If the switch is starting to fail, it might cause what you are experiencing. The oil switch is a safety feature that prevents the pump from running if your engine stalls. The switch is located on the port side of the engine just above the oil filter (or where the oil filter would normally go without a remote filter installation). There are two wires leading to the switch. When the problem occurs, you could temporarily put a jumper wire across the two leads so the pump will run continuously with the key in the run position. If the engine starts and runs fine (check your oil pressure immediately) , then it’s the oil switch (not to be confused with the oil pressure sending unit). Don’t leave the jumper wire connected. It’s just for testing purposes. The switch is there for a good reason. If the carb float sticks and the engine stalls, you don’t want a bilge full of gas.

Thanks Cyborg! it sure makes sense and seems to fit the situation. We will check it out today and let you know the results. The problem is that it is a little incosistent so cannot be sure we have it fixed until an extended trial. However, i am familiar with the oil switch - had to replace it a few years ago and will check it out as you suggest. Because it is not hight cost, I will replace it anyway and be sure the electrical connections are clean. This explains how it gets some gas to run on the start cycle and then shuts off on the run circuit.

Dick

First time out this season, 2012. 2001 Stingray LS. 4.3 litre. Same thing happens. Runs for a few seconds... then stalls like choke open.... or no gas. While on water, checked the safety kill switch with lanyard... that was ok. Took boat home, Hotwired the fuel pressure sensor (two wires)... and Voila. Engine runs without stalling. Thanks for the post and terrific suggestions.