Gas odor after running twin 350's

[DSC]

Probably a stupid newbie question...but i have twin 08 Yamaha 350's on my 360 Express and have noticed a mild gas smell from the outboards and a small sheen in the water after running the boat for a while. Both the smell and film dissipate after a while, and only occurs after running. There is no gas smell onboard. The engines have been running flawlessly. I have only had the boat for a few months so Im not sure if this is a new occurrence. Is this something that I should be concerned about?

 

[Fishtales]

Might want to remove the cowlings and chase the fuel lines. You may have a small leak.

 

[seasick]

Unless some sort of maintenance was done incorrectly, I doubt that you would develop a leak or whatever on both motors at the same time. Try running one motor at a time to see if indeed only one motor has a problem and go from there.
If maintenance was done to both motors just prior to this problem occurring, I would look at that work first.

 

[journeyman]

I would do as Fishtales suggests. I have the same motors and do not have any gas odor or sheen. Shouldn't be to hard to locate

 

[SkunkBoat]

If you are sure you are smelling raw gas, definitely figure it out asap.

If you don't find a gas problem, consider the possibility that its hydraulic fluid from one of the tilt rams.
That wouldn't explain a strong gas smell but sometimes seeing something out of the ordinary leads us to smelling things that were always there.

 

[DSC]

Update....so I had a guy at the marina check out my engine and he thought he saw a dried up area of fluid under the fuel cooler (his term). He recommended a Yamaha service guy who can out, did a thoughrough check and was unable to find anything leaking. He merely stated that the engine runs rich, and doesn’t have any issues. He stated that the sheen in the water was simply exhaust.

I still notice a much stronger gas scent from that engine compared to the other though. I guess I will just keep a very close eye on things.

Thanks again for everyone’s advice. It is always really appreciated.

 

[seasick]

I mentioned, do both engines leave that sheen? You should be able to test at the dock. Since it seems to you that one Onegin smells of gas more than the other, you probably have an issue on the 'smelly' motor.
I don't buy the 'running rich' argument. Gas in the exhaust can get there in a couple of ways; one of course is a leak that drains into he outer exhaust housing. The second is excess gas in the exhaust itself, either too much fuel or incomplete combustion. Having a tech dump the ecu data might point to a problem. Over time, a leak will most likely get bigger and an over rich situation will lead to fouled plugs.
You could have a bad injector also. The diagnostic unit should be able to detect that (I think).
If you have fuel usage data on your displays, compare the usage and burn rate of each engine. Leaks will often show up as higher gallons used for the motor with the leak.

 

[suzukidave]

if the guy really did check the motor out properly, it sounds like either a tiny fuel leak somewhere reaching the water via gravity or else unignited fuel (not running rich), meaning a spark issue.

to be running rich enough to leave a visible sheen of exhaust in the water without throwing a code or symptom a yamaha tech would detect is hard to believe. o2 sensors get lazy before they fail but not that lazy.

 

[DSC]

Sounds like I may need a third opinion. I had the boat in Fort Lauderdale initially, super easy to service, but moved it inland to Lake Lanier in Georgia...much more difficult to find certified Yamaha mechanics who know a 350.

 

[DSC]

I mentioned, do both engines leave that sheen? You should be able to test at the dock. Since it seems to you that one Onegin smells of gas more than the other, you probably have an issue on the 'smelly' motor.
I don't buy the 'running rich' argument. Gas in the exhaust can get there in a couple of ways; one of course is a leak that drains into he outer exhaust housing. The second is excess gas in the exhaust itself, either too much fuel or incomplete combustion. Having a tech dump the ecu data might point to a problem. Over time, a leak will most likely get bigger and an over rich situation will lead to fouled plugs.
You could have a bad injector also. The diagnostic unit should be able to detect that (I think).
If you have fuel usage data on your displays, compare the usage and burn rate of each engine. Leaks will often show up as higher gallons used for the motor with the leak.

The smell is definitely coming from the Starboard engine. I’m still not sure which side the sheen is coming from, but will check it out again this weekend. Thanks for the advice on checking the fuel consumption, I’ll take a look at this weekend.

 

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So...as I continue to smell gas from the starboard engine, I went ahead and had a third Yamaha mechanic look and he too was unable to find anything after a thorough running of the engine.

So today, after a day of fishing, I noticed that there wasn’t a gas smell until I trimmed the motor all the way up. Doing this also caused a sheen to form in the water. In fact, some of the little amount of water exiting the splash well scupper by the starboard engine smelled strongly of gas.

Does the fact this occurs only with a trimmed up motor aid in a diagnosis?

 

[journeyman]

Does the fact this occurs only with a trimmed up motor aid in a diagnosis?

Just a thought on this... The fuel line exits the wall in the splash well area and enters the rigging tube going to the engine where your primer bulb is located. That's how mine is rigged. There could be a leak in that line from chaffing when you put the engine up and down and it manifests itself when you raise the engine. Have someone raise and lower it while you get get a good look. There could be fuel pooling inside the rigging tube and it comes out when you raise the engine causing the attitude of the rigging tube to change.

 

[seasick]

I agree that there could be a leak in a fuel line that is routed through the rigging tube but there could also be a leak that causes fuel to pool in the lower cowl and drains out when the motor is tilted up. One simple test I might try is to tilt the motor up, make sure the motor well is dry and pump the heck out of the primer bulb. Note if the bulb is firm to start. If not there may be a leak between it and the fuel pump. After pumping the bulb look/smell for leakage.
Since the fuel lines upstream(towards the tank) of the fuel pump are under lower pressure when the motor is running than when sitting, you usually don't see more leakage when running. I don't know what on motor fuel filter you have but if it is the removable clear bowl type, check that for leakage especially after pumping the primer.

If you have a leak in the fuel hose between the tank and the primer bulb, that is a bit harder to isolate. One way other than removing and inspecting the hose is to install a second primer bulb between the tank pickup and the fuel hose,. Pumping that should result in a firm bulb that holds pressure. If there is a leak, the pressure will drop and you should see/smell fuel.

 

[DSC]

Thanks for all of the advice. I will try all of those things on Wednesday. I have also been reading about the possibility of fuel leaking out of the VST when the engine is raised. Has anyone encountered this?

 

[journeyman]

You should be able to locate any fuel leak using your eyes and nose. At the dock with the cowling off, as stated, pump the bulb til hard and get in there and look around. wipe down dirty / oily surfaces with a rag. Use a flash light. Run the motor. Rev it up with the neutral lock depressed. 10 to 12K should be plenty. Get up close and personal. Poke, prod and jiggle. Have a helper lift the engine while you're looking. Do it multiple times. If the leak is enough to smell and leave a sheen, it should be easy enough to find if you put in the time.

Was the VST serviced? There is a Schrader valve at the top to relieve pressure for servicing. The drain is a needle valve which connects to a small clear hose.

 

[seasick]

Thanks for all of the advice. I will try all of those things on Wednesday. I have also been reading about the possibility of fuel leaking out of the VST when the engine is raised. Has anyone encountered this?

The VST tank portion is under pressure when ignition is on and also when motor running. I suppose it is possible that there may be a leak but I would think it would leak all the time. The VST has a float and needle valve that if not working correctly will allow gas to overflow. If as mentioned that overflow drains into the lower cowling, that could explain why fuel drains when the motor is tilted. It shouldn't be hard to see if the tank is overflowing, just reroute or remove the overflow hose and watch for fuel as the motor runs. One other idea to try. Dry off the outside of the cowling (lower and mating ring) as well as dry off the flex rigging tube. Wipe with paper towels until the towels don't really smell of gas. Now run the motor as you normally do and then shut down and raise the motor. Let is it for a while and look for the sheen on the water. When yo see that sheen, use new paper towels and wipe those areas again, after wiping each section, look and small for gas. If the gas is leaking out of the cowling or the rigging tube, you should be able to detect it with the towels. You may want to also wipe the motor well to remove residual fuel.
It's an interesting problem. I can't wait to hear the solution.

 

[suzukidave]

So...as I continue to smell gas from the starboard engine, I went ahead and had a third Yamaha mechanic look and he too was unable to find anything after a thorough running of the engine.

So today, after a day of fishing, I noticed that there wasn’t a gas smell until I trimmed the motor all the way up. Doing this also caused a sheen to form in the water. In fact, some of the little amount of water exiting the splash well scupper by the starboard engine smelled strongly of gas.

Does the fact this occurs only with a trimmed up motor aid in a diagnosis?

well that would strongly indicate it is a leak, not a case of running rich.

you should have your fuel system pressure tested.

if that does not work, buy some uv dye marker to put in the fuel and a black light flashlight. you should be able to find the problem.

 

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Final update....after multiple examinations of the starboard engine, a bad gasket was found on the VST which was casing the fuel to leak. The gasket has since been replaced and the problem solved. I guess the fuel was just pooling and only leaking out of the cowling when the engine was up. Thanks again for everyone’s advice.

 

[Ky Grady]

Thanks for the update. Glad you found it. Small things like that have a way of aggravating you trying to find it.

 

[Fishtales]

Well you know what the issue was and it is corrected. Win-win.