Fuel Delivery

[Themanofsteel]

I have a 1988 Force Outboard on a Bayliner Capri. Lately, when the gas gets low to about a 1/4 tank, the boat struggle to get gas. Never did this before. When it has plenty of gas it's fine. Whenever its low and I squeeze the primer bulb it accelerates but eventually starts to struggle again. The air flow is clear and good. Not sure why it only happens when it's low.

 

[Jiggz]

I would look at the tank vent for clogging. If you really want to test if it is the tank vent, then when your fuel level goes down low and the engine struggles, remove the gas tank cap and see if this will make the engine not struggle. If it DOESN'T struggle with the gas cap off , then it is a vent problem.

 

[Themanofsteel]

I actually tried that last weekend. Didn't have any effect. Still struggled with gas cap off. Could it be the primer bulb? It's fairly new. I replaced it a year ago because the other had a leak.

 

[Nordin]

Have you checked the tank pick up?
Some tanks have hoses in the pick up and you may have a crack in the hose at bit up from the bottom and this will make the engine sucking air when low fuel level.

I have had this issue with a snowmobil, ran great with high fuel level and when it went down the engine started to shut of back and forth.

 

[Themanofsteel]

Thanks. Ill check that.

 

[Themanofsteel]

I've not checked the pick up yet but I took my boat out today. I was wrong about something. It seems that my boat struggles even when the tank it 3/4 full BUT, it only occurs either from a lengthy trip or during some pretty significant ocean turbulence. Again it never did this before. Any thoughts?

 

[jerryjerry05]

Sounds like gunk in the tank.
​The Bayliners (depending on the year) used stainless tubing in their metal tanks.
If my memory's right the 88 Capris built in tank was metal.

If the boats sat for any length of time it can have gunk build up.


Try to siphon off the fuel and when it's low or empty pull the sending unit and see what's in the bottom of the tank.

IF?? it's clogged, clean it out, NO vacuums .BOOM!!

 

[Themanofsteel]

You're right. It's stainless steel. How would I clean it out?

 

[Jiggz]

The pick up tube sucks from the bottom of the tank regardless if the fuel is low or high. So if this is gunk it must be floating gunk! But you said if you prime it then the engine starts to run fine again. So it is not about the pick up tube getting clogged. Instead, it is the fuel pump losing suction when the fuel is low. Which means the fuel pump diaphragm could have been weakened or has a small hole in it or an air leak somewhere in the fuel system.

When tank is full or high, there is positive pressure at the bottom of the pick up tube. And the weakened fuel pump is able to deliver. However, when the fuel gets low there is no more positive pressure and the weakened fuel pump in unable to deliver anymore or because a small air leak is preventing it from doing so.

If you had the clear fuel filter you should see bubbles when the fuel pump struggles to deliver if the cause of the problem is an air leak. If there are no bubbles, then it could just be a weakened diaphragm.

 

[Themanofsteel]

I had replaced the diaphram after the first time it happened thinking it might have been the problem. Its still did it again even when the tank was 3/4 full. I feel like it occurs in turbulent waters and on a lengthy drive.

 

[Jiggz]

Do the clear filter installation and check for bubbles. This is an indication of air leaks in the fuel system. Finally, if this does not disclose the problem it's time to use an external tank.

 

[Themanofsteel]

Ok. I have a clear fuel filter on already. I'll check it. So I'll look for bubbles when driving?

 

[jerryjerry05]

You have any inline connectors?
​They can leak and suck air.

 

[Jiggz]

Ok. I have a clear fuel filter on already. I'll check it. So I'll look for bubbles when driving?

Yes, while driving even better at high speeds. So you will have to drive the boat with the top cowling off. Meaning you will need a second person to look over it or do the driving. If you see bubbles you have air leak.If there are no bubble check if the clear fuel filter gets real low (less than half) or empties. Check the primer bulb to make sure it doesn't collapse. If primer bulb collapses, then there is a clog between the primer bulb inlet (faulty check valve) and fuel tank pick up tube. If it doesn't collapse, then there is a clog or restriction between the primer bulb outlet (faulty check valve) and the fuel pump.

If none of the above is the problem, then it can only be the fuel pump. You can either double check the work you did on the fuel pump or troubleshoot using an external tank with different fuel hoses and primer bulb.