Can too much air getting into the fuel tank make a difference

[howard6212]

My engine keeps cutting out. I think its being starved of fuel. Filter in the external tank seems OK. But the fuel gauge is leaking when I shake the tank. Therefore letting in air. Am using new fuel so no contamination. Engine is a Mariner 30hp outboard.

[jwalker]

You can't let too much air into the fuel tank. Check your fuel supply for air leaks; perforated tubing, leaking seals at the connections, leaking connections where they are push on. Check for blockages, possibly intermittent and check the fuel pump operation.

Firstly, is you have access to an alternative fuel system, try it and this may eliminate a fair amount of your system as being the source if the problem.

Edit. It's just occured to me that when you mention the fuel gauge is leaking, if it's the type of tank fuel gauge which also has a push-in connector for the fuel tube attachment, it's possible the connector is leaking rather than the gauge. Some of these fittings have an O-ring inside them into which the tapered fuel connector slides. If the O-ring is damaged, the system can suck air at this point. The connection to the Mariner engine may well also have an O-ring which is worth checking. Many years ago I had this as a problem on a Mariner 30 (The Yamaha Origin type.) and the engine would run fine until it was used at full throttle for a short while. A small nick in the O-ring was all it took to cause the problem.

Be very methodical and you'll find it in the end.

[Nasher]

Are you sure enough air is getting in to the tank?

vacuum in the tank is a classic cause for engine cut out and then re-start once the pressure has been restored.

Nasher.

[codprawn]

Reading this again I suspect the fuel gauge is leaking because the breather is blocked and there's a hell of a vacuum - it maybe the only place air is getting in. Not being funny but you have unscrewed the breather vent haven't you?

[howard6212]

Thanks I think you're right. I'm new to this, but when pumping the fuel to prime the engine I have alwas felt that the pump ball is not getting hard enough as if I am pumping air with the fuel.

[9D280]

Yeah, if it;s the "bayonet" type connector, the O- ring is a possible cause - if you leave it long enough, not only does air get in, but when you stop the engine, fuel gets out....... How old is the connector? (I discovered that on an old metal tank from C.1985)

Also I've found that trying to mate the plastic and the metal versions of that connector don't always talk to each other as well as they should. The release pin on the plastic ones seem to be longer than the metal ones, so the O- ring doesn't seat properly and the inevitable leak ensues) I use them on my tanks 'coz I think the bayonet is a lot easier to change over with cold wet hands than the suzuki "fingertip" operated one once the first tank is drained.

Hope this helps. O- rings are (should) available as spares from your local dealer....

[al40]

Originally Posted by howard6212

My engine keeps cutting out. I think its being starved of fuel. Filter in the external tank seems OK. But the fuel gauge is leaking when I shake the tank. Therefore letting in air. Am using new fuel so no contamination. Engine is a Mariner 30hp outboard.

You'd be amazed at how much pressure develops in a fuel tank when it's all sealed up. I've had one of these 5l plastic fuel containers bulging hugely when either in the boot of the car or in the garage (hence why they have max fill lines!). Shaking the tank also increases the pressure in the tank so it will likely be fuel vapour coming out the tank rather than air going in.

One of my old Suzuki tanks leaked badly out of the guage which was in the same place as the connector and I think it was the joint between the plastic viewing window and the tank.

A new hulk 30l tank can be picked up for £20 from various placed and you can sometimes even remove the old tank connector and screw it onto the new elbow. If the the guage is leaking, it may be good investment.