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rob935
02-10-2007, 12:08 PM
i have a 93 prostar with the standard 5.8L engine, all is running fine with the engine but there is a very distinct fuel odour and there seems to be fuel coming out of the exhaust although there doesnt seem to be alot of it but enough to stain the surface of the lake whilst stationary,

any ideas guys..??

Andyg
02-10-2007, 12:12 PM
It is probably fuel coming out throught the gas tank vent on the back of the boat. If the tank is full the gas can slosh around and find its way out the vent. There are things you can put in the vent line to make sure fuel doesn't get out and water doesn't get in.

I found this, but I don't know if it will fit the vent line in your MC.

Vent Valve (http://www.skidim.com/prodinfo.asp?number=LG-50)

rob935
02-10-2007, 12:18 PM
i have checked the vent which is fine. but there definitely seems to be some kind of fuel mix with the exhaust gases , have drained the oil and carried out a compression test on cylinders and also checked all gaskets so no worries with the engine itself ??

Andyg
02-10-2007, 12:24 PM
Does gas ever come out the vent when you fill up with gas using the pump at the gas station? The vents on these boats do not have any type of seperator valve to keep water out or gas in. There is usually only a screen and the location that tries to limit the amount of water that gets in.

The only way you would have raw fuel coming out your exhaust is if one (or More) of the cylinders isn't firing. I would think you would have problems with back fires though becuase of the fuel would mostlikely burn in the exhaust manifolds. Have you noticed any changes in performance?

TMCNo1
02-10-2007, 12:28 PM
A lot of times, if you fill the gas tank real full and the temp of the gas is cool from being in a tank underground and you then put the boat in the water where the water temp is higher than that of the gas, the gas will expand as it heats up and come out the vent until you use some of the gas in running the boat.

rob935
02-10-2007, 12:36 PM
it happens even whwn the fuel is low...the performance of the boat hasnt been affected either, the odour improved quite a bit after a good service but it is still there,

Andyg
02-10-2007, 12:39 PM
What engine do you have in your boat? I assume it is carburated. You may be running too rich of an air/fuel mixture and the unburnt fuel is what you are smelling. Did you have anyone tune your carb lately?

rob935
02-10-2007, 12:43 PM
its a 351 v8 as far as i know with a velvet drive if that helps, it is a carb model and i havent had the carb serviced at all, have the boat a year now .

JimN
02-10-2007, 12:55 PM
Rob- check the flame arrestor to see if it's dirty and clogged. This will make the boat sluggish and is similar to running with a hand over your mouth, with the added problem of not burning efficiently. Not only will the gas be unburned but it can dilute the motor oil and cause wear. Pull the dipstick and sniff the oil- if it smells of gas, change it immediately and take the arrestor outside, clean it and it may fix your problem. Dirty flame arrestors were probably the biggest single point of neglect on the boats I serviced. Out of sight and out of mind, I guess.

Carburetor cleaner will take care of the gunk on the arrestor. You can use an all-purpose de-greaser if you don't have anything stronger but it will take longer.

rob935
02-10-2007, 12:58 PM
first thing i did when i bought the beast was to scrub the flame arrestor, and its had a full oil and filter change, have kept an eye on the oil but no sign of fuel odour from it though.?

TMCNo1
02-10-2007, 01:02 PM
Carburetor cleaner will take care of the gunk on the arrestor. You can use an all-purpose de-greaser if you don't have anything stronger but it will take longer.


Jim, I use the cheap/cleanup lacquer thinner to wash mine with in a small bucket. It works fast and dries quickly with no odor as long as the arrestor is alum. or s/s for carb'd boats.

JimN
02-10-2007, 01:12 PM
I don't know what is available in Ireland so I included the de-greaser.

TMCNo1
02-10-2007, 01:25 PM
I don't know what is available in Ireland so I included the de-greaser.


Didn't think about that, good call! Thanks!

east tx skier
02-10-2007, 01:26 PM
If none of that checks out, look for stains on your intake manifold below where the fuel line hooks up to the carburetor. I had a guy overtorque mine once and the resulting fuel leak really stunk up the boat. Got it set to proper torque specs and no more leak.

FrankSchwab
02-10-2007, 02:39 PM
Is it as simple as a stuck float in the carb dumping fuel back down the carb throat through the overflows?

WilliM1940
02-10-2007, 02:56 PM
Fuel smells on older boats are difficult to isolate. The winter following my purchase of a gas fumed MC, I pulled the tank, cleaned and leak tested it with water, replaced the fuel gauge sending unit, filler hose, vent hose, rubber gas lines to the fuel filter and engine, replaced and cleaned the fuel filter and did a carb overhaul. The lines were stiff, the filler hose was checkered and stiff, the sending unit gasket was dried out and cracked. Anyway, nothing looked like it was leaking, but the smell went away. Could it be that what you are seeing in the water is oil only and seperate from the gas smell?

east tx skier
02-10-2007, 10:05 PM
Is the overflow vent under the cover? When mine is covered for a while, there's always a bit of fuel smell, but not like there was when I had the leak. There's a noticeable difference.

JKTX21
02-11-2007, 12:20 AM
I guess I need to put this vent valve on my boat. It sloshes a lot of fuel out of the vent when full. Anyone else had this problem?

rob935
02-11-2007, 09:46 AM
thanks for all your input guys,
seems more like a carb problem to me now, there arent any leaks in the fuel lines or at the intake manifold, flame arrestor is clean and the overflow isnt the culprit. so looks like i gotta take the carb out and get it looked at, hopefully that will sort it out. many thanks again.

mash
02-11-2007, 09:57 AM
Pretty sure you've got it nailed. If it's getting into the water as you say, and fuel level has no effect, it's passing through the engine. Probably running rich (should show on the spark plugs). It doesn't take much fuel to spread out on the water and look really bad in the sunlight.

Carbs are neat, 'cause you can fix them when there's a problem. Fuel injection is better 'cause you don't have problems!

André
02-11-2007, 11:14 AM
...Carbs are neat, 'cause you can fix them when there's a problem. Fuel injection is better 'cause you don't have problems!
I love that line...:D