Perkins 4.108 Surging

[Jcarterwil]

Help please....

I have a perkins 4.108 1984 vintage on Alden 44. It has work perfectly since 1984

Right now it is losing prime after a day or two. When it does start it runs fine until it gets to 150 degrees. At that point it starts to surge. If below 1500 rpm it stalls out. If above it runs away. But the kill lever shuts the engine down. So still seems like fuel. After it surges and is shut down it loses prime again.

End of last season we did seem to have bacteria in the tank and now have that clean. We are chasing leaks. We have used some sea foam to clean out injectors. It has a racor 30m and an on engine 30m filter.

Local mechanics are really not that great. The fuel filter is getting darker again. Not sure how but I feel we might be getting some oil in the diesel.

Lift pump was replaced last year. Noticed this season Oil was high. I suspect we had a leak at lift pump then and mechanic did not drain.we have since drained and it has not risen. But we don't have a lot of hours this season because of problems above. So we might be making oil. Kill lever shuts engine down so do not suspect making oil is cause of runaway.

Maybe when it gets to temp leak increases and governor gets wobbly and it surges?

[donradcliffe]

My 4108 used to start surging when it was time to replace the fuel filter. In your case, it may be air inleakage. I've had a couple of older Racor filter housings be the source of the air leak. See
https://www.cruisersforum.com/forums...ile-27507.html

If your oil level is higher, smell for diesel on the dipstick. Be sure and change the oil ASAP.

[Jcarterwil]

I have shut it off quick so never let the sure play out much. How much did it surge for you, like above 3000?

Will check filter. That was the last thing mechanic played with before this happened.

[Lepke]

Organisms in the tank can make your filter black. If your fuel is old, the biocide included at the refinery is long gone. If you didn't kill the organisms in the tank, they're probably back.

You have an air leak. One way to check is a fuel can connected to your lift pump. If that works, the leak is between the lift pump and the tank. You lose prime either because the valves in the pump are bad, debris is stuck on the valve surface or an air leak usually before the lift pump.
Another way to find an air leak is to make an air connection and use a bicycle pump and pressurize the line and filter. Wrap any connections with toilet paper and look for leaks. Air will escape easier than fuel and sometimes can be heard.

Some people put a check valve before their primary filter to stop fuel from flowing back to the tank when the engine is shut off.
I use 2 micron filters and always use an additive when I fuel or ad one if the fuel is old. My fuel is always clean.

[Warby12]

Blocked fuel filters from dirty fuel will cause surging. I speak from direct experience. Even if the bugs are dead, using the boat in any kind of wobbly water will stir them off the bottom of the tank.