View Full Version : unburned fuel?

08-31-2012, 12:57 PM
I have a 2004 Outback (Indmar 5.7 TBI)

Bought it recently with only 84 hrs.
All runs great, but when im pulling skiers there is a strong smell of unburned fuel and my fuel economy
seems pretty bad.

Put in fresh spark plugs and they look fine after 10 hrs.

I ski behind a number of other boats and do not notice this strong fuel smell.
Seems like it is running to rich.
Temp Guage is reading 180 when hot.
What should I be looking for?

Thank you for any thoughts

08-31-2012, 01:07 PM
What is your idea of poor economy?

Did you look at or change the distributor cap and rotor? If you have weak spark, that could be an issue. I would also check the timing.

08-31-2012, 03:23 PM
Could simply be a characteristic of your boat or your idea of poor fuel economy. Or an injector hanging open

2005 mobius lsv 2900lbs ballast

08-31-2012, 05:45 PM
Seems like if an injector was stuck you would see it on a plug after 10 hours. If the plugs look good and it's running fine with no stumble I wouldn't worry about it.

08-31-2012, 11:42 PM
Installed new cap and rotor as it did show some wear. still no change.
This is TBI not MPI so i dont think a fouled injector would show up on any single spark plug but i will look
into the possibility of a blocked TB injector. Have a neighbor with the same engine and ignition system
and he agrees that my exhaust smells of raw fuel. Any other sensors that could cause a fuel rich condition?
but still allow engine to run well?

09-01-2012, 12:25 AM
Just a thought but may want to check your venting. There is a vent intake in front of the windshield on each side. As the boat moves it forces air through the engine compartment and out the stern. Your blower running enhances the flow but it will flow through even when the blower is not running. If there is an obstruction or loose hose you may not be venting properly. Also, check your fuel tank vent. Make sure it's all good.

09-01-2012, 07:34 AM
Bump the timing up a tick and try a hotter plug

2005 mobius lsv 2900lbs ballast

09-01-2012, 07:52 AM
The engine is pretty simple. A mix of gas and air are force into the chamber and a spark burns the fuel. The motor runs correctly, so most of that operation is working. You have address the spark with rotor/cap/plugs. It is getting fuel, so the pump is working. The TBI unit should have 2 injectors that you can see in operation when the boat is running. Have you observed those while at idle? I'm no expert on how those injectors would push more fuel, but perhaps you could do an internet search for that info. Checking the timing will let you know if it is set correctly. advanced or retarted timing will still allow the engine to run properly, but could do something like this.

i had a MC boat with TBI. I enjoyed watching it "work" while I was fogging the engine. If one of those injectors was squirting more than the other, you may be able to see it.

09-01-2012, 05:08 PM
Good luck figuring it out. I have a 2004 TBI with close to 1000 hrs that has the same issue. Strong fuel smell and sometimes you see raw fuel in the water. Some days are worse than others. I have tried plugs,wires, rotor, cap, checked to see the injectors are not spewing fuel, had sensors checked etc. Strange thing is the boat runs great.

09-01-2012, 06:21 PM
Im going to check the injector spray pattern and see if one is not atomizing properly. could be gummed up
as the boat had so few hrs since 2004 i assume that it sat in dry dock a lot.