Changed Fuel/Water Separator - Now Engine Acting Funny

[DiamondDave952]

Hello All. I put my pontoon in the lake for the first time this season but, before I did, I replaced the fuel/water separator since it's been a few years (July 2024) since it was last replaced. I replaced the separator with a genuine Yamaha OEM part. I removed the old one and screwed on the new one. I didn't pour any gasoline in the separator (since I didn't have a small tank of non-oxygenated fuel handy) and just screwed it on. I then proceeded to squeeze the fuel bulb to fill the canister. Engine fired right up and I thought everything was good. As I was driving, I notice my RPMs would occasionally surge. What I mean by that is, I could be running steady at 3500 rpm and out of the blue, the rpms would jump to 4000 rpm for a few seconds then drop back down again. This happened multiple times as I was driving the pontoon to my cabin. I only run non-oxygenated fuel. I have never have this happen before and was looking for feedback on what is causing my engine to act funny and if I need to bring it in to the service dept. to have it looked at. I was wondering if I have air in my fuel line from replacing the fuel/water separator? Anyone experience something similar? Thanks!

 

[Lay Lake]

It sounds like air in the line. Always try to pre-fill fuel filters before installing them. If the engine will stay running the air should work it's way out. If it quits or keeps acting up, you may have to bleed the fuel system. Im not sure of the procedure for a yamaha outboard, but I'm sure it involves loosening a screw and pumping fuel until clean clear (no air) fuel comes out.

Ive changed hundreds of diesel tractors fuel filters and almost never have problems when I pre-fill the fuel filters. When I dont and follow the procedure to bleed the air, it usually makes me remember why I pre-fill them.

 

[DiamondDave952]

Thanks for the feedback. The last time I changed the separator, I did prefill the canister and didn't have any issues. Will I do any damage to the engine if I keep running it while the air bubble makes their way out?

 

[Potomacbassin’]

Another possibility is the seal/o-ring on the separator is allowing air to suck in. I would pull the filter and make sure there isn't dirt/debris/corrosion on the mating surfaces, put a little lube on it and retighten and see if that helps.

 

[Angela & Michael]

This is where a squeeze bulb is handy on a four stroke engine. No, the air will not hurt the engine in the fuel line, but it won’t help it either. Your best bet is to take off the filter…fill it full of gas put it back on and squeeze the bulb till hard. Good luck.

 

[DiamondDave952]

I wanted to follow-up on the issue I wrote about above. I replaced my water/fuel separator again and this time, I filled the canister before installing it. Took my pontoon out with a friend today and put a few hours on the engine. The motor appears to be running fine now. RPMs are solid not fluctuating like before. When I got back to my dock, I went to squeeze the primer bulb expecting it to be firm, instead it was soft. Squeezed it a few times and couldn't get it to be firm. Any thoughts on why that is?