Engine backfires and dies

[WhereBob]

I have a 1990 mercruiser 3.0L in a 1990 bayliner I just bought used. The guy told me in the 4 years he has had it it has run flawlessly. Well out on my first run with my new boat. Fired up great and purred nicely. Got it out on the water and throttled up to 25mph, no problems. After 5 mins it backfired but kept running fine. another 5 mins it backfires twice sputters twice and keeps going. Then it lulled almost died but came back and keeps going. Another 5 mins later we a cruising around 5 mph and it just dies. Took about 5 mins of on and off cranking but finally started after a 10 sec crank. Ran good all the way back to the dock. As I throttled down to cruise in it died again. This time it started right up.

The carb was rebuilt last year he tells me?

 

[CharlieB]

Re: Engine backfires and dies

Remove the fuel tank dip tube, use a thin plastic tube to reach the very bottom of the tank and pull a fuel sample.

Look for water accumulation. Either condensation inside the tank or bad gas and the accumulation gets to be enough that it is finally picked up and into the carb, just a drop at a time is enough to cause your symptoms.

Once proved, jack and block the trailer such that your access to the tank is the lowest part of the tank. Let settle for a couple of hours then siphon off until only clear clean fuel comes from the tank bottom.

Installing a fuel/water separating filter is always a good investment, but tank 'purging' every ten years or so never hurt.

 

[mthieme]

Re: Engine backfires and dies

Also check underneath your distributor cap for condensation and/or cracks.

 

[WhereBob]

Re: Engine backfires and dies

Well put the rabbit ears on and fired it up in the driveway, ran perfect for over 10 mins with no problems. Throttled up in gear and even pushed the throttle down on the carb to below idle speed to try to get it to die but it held.

It was really windy with white caps on the water so the boat was bouncing around pertty good. Could that of effected something?

Let settle for a couple of hours then siphon off until only clear clean fuel comes from the tank bottom.

So if water is clear and gas is clear how do I see the water in the gas? I take it water is heavier than water and settles to the bottom?

Thanks for all the help

 

[achris]

Re: Engine backfires and dies

...So if water is clear and gas is clear how do I see the water in the gas? I take it water is heavier than water and settles to the bottom?

Thanks for all the help

Water is completely clear, petrol has a reddish purple tinge. Yes, water is heavier than petrol. Water weighs 1kg per litre, petrol weighs 740g per litre.

Chris.........