Mercruiser 140 BackFiring When boat is on Water

[chicubs08]

Why does my Boat Backfire when its on the water. and on land with the ear muffs it doesn't? I have a mercruiser 140, 3.0 L, 4 Cylinder. I have giving it a complete tune up. including a rebuild carb. Any help will be greatly appreciated.

 

[maxxman04]

Re: Mercruiser 140 BackFiring When boat is on Water

timing off?

 

[towman818181]

Re: Mercruiser 140 BackFiring When boat is on Water

could the angle of the boat once in the water be pushing some bad fuel into play

 

[cooter2506]

Re: Mercruiser 140 BackFiring When boat is on Water

You have a lean fuel condition. Just acts up under load. Look up in the adult only section for the post how to check your fuel system. Do all tests it will tell you what your problem is

 

[BF]

Re: Mercruiser 140 BackFiring When boat is on Water

double check that with your tune up you didn't get 2 plug wires crossed. My Dad complained about the idle and how his 120 mercruiser seemed to stumble with some throttle. He was on about his 3rd time going through it and tweaking the carb etc. While he was doing that I got curious and looked up the firing order and traced the wires from the distributor... he had 2 wires crossed. After switching them around it was MUCHO better. But we were surprised how well it ran at mid range with the ignition being whacky.

Barring that, you might also consider going back to your old distributor cap as a test (if you changed it)... backfiring is usually timing being way off.

 

[fcveazey]

Re: Mercruiser 140 BackFiring When boat is on Water

I'm having some of the same issues, only my boat runs like a pro-street dragster for 30 mins, then starts acting up. Someone sent me a mercruiser service bulletin on vapor lock. Its very interesting. I'll try and forward you the link, but I think it'll be up top in the adult section.