Engine RPM cycle at cruising speed, Penta 3.0 GS

[NYfourwinns]

This is a 98 Penta 3.0 black inboard motor, it was running fine but at one point while cruising at around 3K rpm, I noticed the engine rpm dip a little every 5-10 seconds. It is more pronounced at higher rpm, and if going at 2K it is less of an issue, and it would idle fine. Feels like fuel starvation. Full tank of gas.

I did try to check fuel filter prior to this trip, and took it out for inspection. It looked not bad, relatively clean, no water, but I did mess up one section of filter element where it meets the rubber seal when I was removing it. I can tell that gas is probably not filtering by going through ceramic element but bypassing through the newly created opening in it. Could that create a problem? It did run fine for about 15 minutes before this issue surfaced. New filter element is ordered, and I will be also getting water separating filter per advice of experts here.

What do you think is an issue here? I am new to this type of engine. Thanks in advance!

 

[NYfourwinns]

Re: Engine RPM cycle at cruising speed, Penta 3.0 GS

Solved! This filter bowl is hard to get to, and impossible to see without mirror. The short answer to the problem, the rubber gasket was there, but the next day it fell out and I did not check for it when installing the filter, assumed it was there since I never removed it. I found it later under the engine on the other side.

This time I disconnected and removed the pump, and figured it's a good time to take it apart and do maintenance on it. All moving parts were good, and membrane is fine. Looking at the paint, I can tell it was never apart since new.

What was strange, it was painted all around, inside as well.:facepalm: I have not seen anyone paint fuel components inside. The bad thing -paint appeared in some pots as if someone applied paint remover, mushy stuff. I cleaned up all loose paint by scraping it off, then blow it clean with a compressed air. Assembled it together, new filter with gasket, and mounted it back on the engine.

The initial problem was caused by air getting sucked in when in demand for fuel at higher RPM. So, simply speaking, make sure all your connections and gaskets are nice and tight, and not missing

Enjoy!