Is it water in the fuel?

[jfw432]

I've been struggling with my engine more regularly lately. I always thought water was getting in the fuel because the power would start to die off, pick back up, and repeat until it eventually sputters out. After a few minutes of cranking, starting, variable revving, and dying again, the engine will start and act normal again. So water in the fuel seemed to be the most likely. It started a couple months ago and has gotten more and more frequent to point where it happens 2-3 times in an outing.

I've done a variety of things to the fuel tank vent to help eliminate water intrusion including adding an air compressor style water separator which won't allow any liquid through the line. Well I'm still getting what seems like water in the fuel and last night even unhooked the vent line completely and was still getting the problem.

I'm beginning to think this isn't a water intrusion issue at all. Would a failing mechanical fuel pump exhibit a similar problem or not wanting to rev or sputtering out?

[strad]

Well I remember years ago our family's 86 suburban (5.7 4 bbl carb) suddenly didn't want to run properly under any load at all, but it would idle fine. When our mechanic tested fuel pressure, it was about half of spec. With a new fuel pump it ran fine again. So if it were me, to eliminate the fuel pump from the equation I would check fuel pressure, ideally while the symptoms are present.

Edit: you don't mention what exactly you're working on. That would probably help the smart ones around here lol. I assume it's carbed or you wouldn't have mentioned a mechanical fuel pump.

[jfw432]

Yeah it's a carbed 351w with a mechanical fuel pump.

[JimN]

Originally Posted by jfw432

I've been struggling with my engine more regularly lately. I always thought water was getting in the fuel because the power would start to die off, pick back up, and repeat until it eventually sputters out. After a few minutes of cranking, starting, variable revving, and dying again, the engine will start and act normal again. So water in the fuel seemed to be the most likely. It started a couple months ago and has gotten more and more frequent to point where it happens 2-3 times in an outing.

I've done a variety of things to the fuel tank vent to help eliminate water intrusion including adding an air compressor style water separator which won't allow any liquid through the line. Well I'm still getting what seems like water in the fuel and last night even unhooked the vent line completely and was still getting the problem.

I'm beginning to think this isn't a water intrusion issue at all. Would a failing mechanical fuel pump exhibit a similar problem or not wanting to rev or sputtering out?

If you want top rule out water in the fuel, you'll need to take a sample at the pump. You can check fuel pressure but it's never very high, anyway. All it needs to do is fill the bowl, not atomize in the cylinder- the wet manifold/vacuum handle that.

It could be a lot of things- all related to fuel delivery, or not. When it bogs, squirt some gas into the carb and see if it kills, or runs better. If it kills, it was too rich already. If it runs better, it could be a power valve, float, needle valve,....

If it revs fine in neutral but not under load, make sure the timing is correct and the gap/dwell are set to spec. If it has electronic ignition, make sure the timing is right. If you can get a spark intensity tester, use that, too.

How long since the plugs, wires, cables and rotor were replaced? Have you cleaned the flame arrester?

[jfw432]

I am putting brand new wires, cap, plugs, and rotor on this winter but haven't replaced anything but the plugs since I bought it 2 years ago. The carb was rebuilt mid summer and it could be a problem with the rebuild kit I installed but it ran so much better after I rebuilt it that I don't really suspect that. The flame arrester is a little black but it was cleaned a couple months ago.

If I have problems, it has the same problems in nuetral and under load. When I'm trying to clear up the problem, I'll rev the engine in nuetral and when if it starts to die above around 2-2.5k rpms, I'll give it more gas and it'll rev. If it starts to die below about 2k rpms, I have to back off the throttle to keep it alive. If I squirt a little fuel in the carb prior to cranking it, it will usually run a little cleaner. Sometimes that will clean it up completely and others it will only work for a few seconds just like I had never done it.

I'm getting ready to pull the engine out of the boat for winter mods and will be doing a leakdown check fairly soon to see what else could be wrong.

[jgraham37128]

Have you replaced the fuel filter?

[jfw432]

Yes I replaced the fuel filter a couple months ago.

[JimN]

Originally Posted by jfw432

I am putting brand new wires, cap, plugs, and rotor on this winter but haven't replaced anything but the plugs since I bought it 2 years ago. The carb was rebuilt mid summer and it could be a problem with the rebuild kit I installed but it ran so much better after I rebuilt it that I don't really suspect that. The flame arrester is a little black but it was cleaned a couple months ago.

If I have problems, it has the same problems in nuetral and under load. When I'm trying to clear up the problem, I'll rev the engine in nuetral and when if it starts to die above around 2-2.5k rpms, I'll give it more gas and it'll rev. If it starts to die below about 2k rpms, I have to back off the throttle to keep it alive. If I squirt a little fuel in the carb prior to cranking it, it will usually run a little cleaner. Sometimes that will clean it up completely and others it will only work for a few seconds just like I had never done it.

I'm getting ready to pull the engine out of the boat for winter mods and will be doing a leakdown check fairly soon to see what else could be wrong.

For whatever reason, I saw a lot of bad coil wires on Ford engines. Also, see if you can get Borg Warner Gold series cap and rotor- I use those on my truck and they come with a lifetime warranty. I used them when I worked on boats, too.

Judging by the fact that it runs better when you squirt gas in before starting, it sounds more like a fuel issue.

[mondos829]

Spray wd-40 in the rotor and cap, get everything coated lightly. Fixed my issue, I was having fouling due to condensation in the cap.

[jfw432]

Looks at the plugs today and they look really white like the engine has been running lean but I'm also used to looking at 2 stroke plugs. All of the plugs pretty much look like this. What do you think?