Air is not welcome here!

[Project_Mayhem]

Lately my outboard has been acting erratic. Usually it starts up as normal and then a minute later it might die or worse yet, it will have extreme loss of power/rpm's on our way out of the marina. Keeping it running while we're sailing seems to resolve the issue for the day which leads me to suspect that there's air in the line. Last week I had a lot of issues starting and keeping it running while we were out on the water. I eventually got it running by priming the bulb that's next to the outboard. I kept the electric pump running until we got back into the marina. We replaced the portion of the line that's been exposed to UV as well as the bulb. The engine ran much smoother. The fuel system is a little more complicated than most. All rubber lines have been replaced in the past year or so.

[Tank]- [electric pump for priming] - [Spin on style filter/separator] - [T Fittting]
[T branch 1] - [unreliable inboard]
[T branch 2] - [Brass fittings through transom] - [External priming bulb] - [Outboard]

The brass fittings were sealed with RectorSeal upon installation and the system has been pretty reliable for the past few years. There are a couple of high and low points that could potentially trap air. The brass fittings are probably the highest point.

Here are the items that I plan on checking/replacing:

• Fuel line to outboard connector will be replaced with a new OEM part
• Old, but known good fuel filter
• Put the electric pump after the filter
• Pressure test the lines??

What are the suggested techniques for finding leaks in this application? Could I create a high point in the system for air to travel to instead of letting it get sucked up by the engines?

 

[Benny17441]

Look for fuel leaks when the engine is running, usually the locations where fuel leaks out is the same location where air enters the system when the engine is shutdown.

 

[justsomeguy]

O rings in the fuel connector to the tank? Dip tube inside the fuel tank? Really, anywhere along the vacuum side of the fuel system, i.e., before the fuel pump.

 

[Project_Mayhem]

I picked up some cheap in line filters to use as a sight glass. Looks like there's a ton of air in the line. Below is a video just before the engine died. As an experiment I connected a T fitting, and an additional filter with one end closed off. The filter is now the highest point in the fuel system. I'm guessing this will help the symptoms but not cure the issue (hmmm... sounds like our healthcare system). I set this up after recording the video. Here's a rough diagram of how it's configured:

Capped Filter
acting as air chamber
|
|
===> Outboard
|
|
Fuel Supply

Video: IMG_7334.MOV

I've seen clear priming bulbs on other equipment that have air in them. How much is acceptable? Would a check valve in the system help keep the system pressurized while not in use?

 

[WayneH]

If you run the priming pump and don't have fuel leaking between the pump and the outboard, your leak is between the pump discharge and the tank. Once the priming pump is turned off, the entire fuel system up to the new clear filter is under vacuum and can let air in.

 

[Project_Mayhem]

I let the motor run while working on other things today. My test probably helped a bit but it wasn't enough to keep the motor running. So, I started investigating. The T fitting that branches off to the two motors had what looked like varnish on it. Clearly a leak there. I then started checking the size of the fuel lines. Strangely enough the one leading to the outboard had no writing on it. When I picked it up for a closer look, I noticed that rubber had rubbed off on my hand. Definitely the same old line that I had replaced last week. Upon removal I noticed that it was 3/8" line while my T was 1/4". It was replaced with 5/16" since that's what I had on hand. I connected the outboard directly to the fuel filter, bypassing the T for the time being. Upon removing the wood panel to access the fuel line going through the transom I found something I hadn't expected - A ratchet with three extensions and a socket taped to the fiberglass. It had been there so long that some surface rust had started to form on one of the extensions! I clearly forgot about it when I was rebedding deck fittings a few years back. Anyways, the motor started up after priming it. Some air for the first minute but after that there was virtually none. I let the motor run before going out, then let it run while I washed the boat. Not only did it keep on running but it ran smoother, stronger and much faster than before. The tiller was actually shaking a bit under full throttle. I suspect this problem had been gradually getting worse for a long time.

The little in line filters confirmed my suspicion that there was air in the line and helped confirm the resolution. The moral of the story is don't forget to check the basics

 

[Project_Mayhem]

I forgot to ask - Can I use a 5/16" hose on a 1/4" barb without any potential for future issues?

 

[jibes138]

Make sure your priming bulb is mounted vertically with the flow direction pointing up!