fuel flow problem since relocating the tank

[warren631]

I needed more space in the laz for storage so I relocated the large fuel tank from the laz to the cockpit under the tiller. Now I seem to have fuel flow problems. Now the fuel tank is above the outboard motor and the fuel lines run downhill to the motor. After priming the motor runs a few minutes then cuts out. I replaced the fuel lines with clear pipe so I could see what was going on. The highest part of the fuel pipe (between the tank pickup (on top of the tank) and the squeeze priming bottle) contains all air (I am sure there are no air leaks so its probably the same air that was in the pipe before fuel entered it). When I squeeze the prime (many times) a small flow of fuel trickles past the higher 'air section'. How can the air be made to escape? I guess that any air in the fuel line is normally supposed to escape through the engine. Would an anti siphon valve fix the problem? Is there a valve or something that lets air out but stops fuel escaping? Should I need to disconnect the fuel line connector from the motor and hold it up high and prime the fuel and fill the entire fuel line (holding the valve at the engine connector end open) and allow the air to escape and then reconnect it to the motor and then never run the tank empty? Suggestions (other than putting the tank back into the laz)? Thanks.

[Banner_IV]

A little air in the line should not be a problem, and should work itself out. I would check the fuel filter and fuel pump since the engine will fire after priming. Also check that there are no cracks or leaks in the primer bulb and hose that would allow air in and loose prime.

[Jimmyt]

Although it's not totally clear in this pic, the 26m fuel tanks are above the power head, and the fuel hose runs downhill to the motor. So, moving the fuel tank should not have caused what you're seeing. Apologize for the motor nudity - pump impeller progress pic...

I agree with Banner_IV.

I would replace the o-ring in your tank hose fitting, or buy a new fuel hose with new fittings. If that doesn't get it, you may need a fuel pump.

If I understand you, you pump the priming bulb; the engine starts and runs a few minutes, then dies. If you immediately pump the priming bulb again, will the engine start again? If priming again does not result in a restart, you may have something else going on...

If priming reliably results in a restart, you either have a leak in your fuel line/connections, or your fuel pump is done.

Good Luck and keep us posted!

[warren631]

It only keeps running if I keep the throttle full out. If I unscrew the drain in the carburetor bowl then lots of fuel runs out. The pump seems to give a strong flow when I pull off the fuel output pipe to the carburetor and crank the engine. The clear fuel filter stays full of fuel. With the throttle pulled full out there is no smoke in the exhaust. It seems that the engine is starved of fuel. So I have ordered a new pump and a new carburetor from Amazon so I can return them if they don't fix the problem. Nice to be a good Prime customer.

I am thinking that the gasket between the carburetor and engine intake manifold is leaking so the engine is sucking in mostly air instead of fuel vapor. This would explain my symptoms. So when I replace the carburetor I will put a layer of liquid gasket on all the surfaces. I also just noticed that the gasket must be installed the correct way around and this might have caused an air leak into the engine so not enough vacuum to vaporize and suck enough fuel from the carburetor. What do you guys think? PS its a Yamaha 8 HP 4 stroke.

[Jimmyt]

A vacuum leak will wreak havoc on performance. I finally built a smoke generator to find a vacuum leak in my neighbors LS engine in his project truck. We looked for it for several days. Put smoke in it and found the leak in about 20 seconds.

I would put on a new gasket instead of using goo on it.

If you have an intake leak, that can cause what you're describing.

[warren631]

Thanks Jimmyt. I will let you know. What is a smoke generator and how do you use it?

[Jimmyt]

Mine looks a little better, but this is the basic idea...

[Tomfoolery]

Baby oil and old socks. Who knew?

Old socks - clean, or dirty?

[Jimmyt]

Here is the one I made. I wear all of my old socks, so I had to use cotton balls and a strip of old rag for the wick...

http://67-72chevytrucks.com/vboard/show ... count=1105

[warren631]

I sealed the vacuum leak between carb and inlet manifold. Also replaced the fuel pump. Runs great now.
Why are outboards so finiky. My 6 hp mower has started first pull every spring for the last 15 years. Air-cooling so no water pump to clog up, no fuel pump, no fuel filter, no winterizing, check oil every few years, no manual choke. My 8 HP outboard is a pia.

[Jimmyt]

Glad you got it squared away. A vacuum leak and/or bad fuel pump would impact performance of any engine. If you're speaking of a push mower with gravity feed fuel, simplicity is in your favor. 9 times out of ten, screwing a new plug in will fix a lawn mower, but only because it is so simple. I've had one air cooled outboard. It was not as smooth and quiet as watercooled but almost always ran.

After you've changed a few water pumps, it gets easier. If not, get an air cooled and see how you like it.