Perkins T6.354 help diagnosing a problem

Hello everyone,
For those of you that have the time to indulge me, your advise, time, and experience is greatly appreciated.
A month ago I bought a Mainship 34 mk1 with a Perkins T6.354 160 hp, there is a racor fuel filter before the lift pump.
Okay, so here is what happened: first trip, total of about 11 hours, everything runs fine. Next trip after about 45 minutes on the first day of cruising, rpm surges and engine loses power as if it had ran out of fuel, can’t get the engine to restart, get towed back to marina, bleed the fuel system, and the engine starts right up. What I discover is that if the engine is getting fuel from the same tank as the fuel polisher, it sucks in a lot of air. So, it was user error and I’m back underway.
Here is where the problem starts.
The second day of cruising after about 5 hours, there is about a 100 rpm surge. I snap to attention thinking it’s happening again but after 5 seconds it settles and resumes as normal. I stop shortly after that.
Third day the same thing happens as above but happens 3 or 4 times throughout the day.
Fourth day it starts happening anywhere from every 10 minutes to once an hour. Eventually I have to keep pulling the throttle back to maintain 2000. Then I pull it back to 1750 and it stays there without noticeable surging for the last 2 hours of the day. When I approach the harbor I bring the throttle to idle but the engine will only go down to 1500. I get it into the slip and have to leave for a few days. I get back and the engine starts right up, idles at 700 and has excessive exhaust. Oil pressure and temp were normal throughout all this.
Any thoughts about what is going on?
Thank you for your help.

You have air in the fuel. You are sucking it I from somewhere.
The polishing system should have the return below the fuel level as in very close to the tank bottom so it doesn't foam up as it is returned to the tank.
Air can be coming from anywhere in the system. You need to check, tighten and recheck every connection including the racor filter.
Also part of the system is the fuel pickup tubes in the tanks. They are notorious for clogging and splitting. They shoud be removed and inspected/replaced.
It could also be a clog in the fuel lines, this happened 3 times to me with my old MS1.
All easy stuff, just labor.

jleonard said:

You have air in the fuel. You are sucking it I from somewhere.
The polishing system should have the return below the fuel level as in very close to the tank bottom so it doesn't foam up as it is returned to the tank.
Air can be coming from anywhere in the system. You need to check, tighten and recheck every connection including the racor filter.
Also part of the system is the fuel pickup tubes in the tanks. They are notorious for clogging and splitting. They shoud be removed and inspected/replaced.
It could also be a clog in the fuel lines, this happened 3 times to me with my old MS1.
All easy stuff, just labor.

Click to expand...

Couldn't have said it better myself. This is a difficult problem to discover and there really isn't any diagnostics that can help. As Jay said you just have to spend time going over every connection in the fuel system, as well as the fuel pickup tube, check the Racor for proper assembly (improper assembly will cause exactly this problem) and perhaps finally, plugage.


No doubt many others will chime saying check this because it is what caused their problem. And maybe you will hit on the magic bullet, but more likely a comprehensive approach outlined above will ultimately solve it.


David

Don’t forget to check the fuel tanks vent.
If it’s plugged, you’ll experience abnormally high vacuum, and suck air in locations that would not allow that at normal vacuum levels.

Was the fuel polishing system running during all of these occurances?
What happens if you turn it off?
When was the last time the RACOR element was changed?

Once had exactly same symptom. The grommets (rubber sleeves) that hold the fuel line in the lift pump were swelling when hot and reducing fuel flow. New grommets cured the issue.