surging diesel

[Steve W]

My 1986 Universal M-18, (14 hp FWC) diesel is surging 100rpm at any setting between 1400 and 2000 rpm in gear. No surging in neutral at any rpm, and no surging below 1400 rpm in gear. Fuel is clean, filter is recent, checked the coupling alignment and motor mounts look ok. The only things left I can think of is a bent prop, bad cutlass bearing (was fine in January) or the engine governor has gone bad. There is a vibration between 1400 and 2100 rpm (in gear) that fades a little above 2100rpm. No vibration in neutral. Do I have twp problems or is one problem causing both symptoms? Any ideas? Thanks in advance!

 

[Bob Camarena]

Transmission Slippage

I'm no expert, but have you considered slippage in your transmission? The fact that the surging occurs only under load and not at lower rpms makes me think that slippage might be the answer. The governer wouldn't be different in neutral than in gear. The cutlass bearing and bent prop could be explanations for the vibration, but don't sound like they'd explain the surge.

 

[Dave Emery]

Surging

I would continue to review your fuel system to correct the surging. Most times this is where the problem lies.

 

[Mike s/v Chute the Breeze]

Fuel Flow

I agree with Dave, to continue to look at your fuel system. Fuel oil is funny stuff it will allow green moss to grow in your tank and may not shut off fuel flow, but will restrict it just enough to allow your engine idle but surge under a load. I'd blow out the lines and take a look in the tank.. also check your air filter, but it's pretty hard to get that dirty enough to starve the engine but it might.Mike mosilver@netnitco.net

 

[Tom Lincoln]

Maybe fuel contamination

Has the boat been sitting idle for a long period of time, or have you used a full tank of fuel recently. We bought a used boat that had sat idle for part of a season on top of that it had a 50 gallon fuel tank that was seldom turned over in a season. The result was algae build up in the tank. It was in the tank and fuel lines as well. I had the tank cleaned and used a shock treatment of Biobore. Also make sure you have changed all the fuel filters. Some engines have a main Raycore plus smaller filters on the engine.

 

[Richard R]

surging

Sounds like a fuel supply problem. I've seen this happen with a very dirty filter. But if the filter has been changed recently, there's a chance you have some air left in the lines. Try re-bleeding the fuel lines starting at the filter, then at the bleed screw on the injection pump, and finally by loosening the nuts on the fuel-delivery pipes at the injectors. You may have to repeat the cycle a couple times to remove all the air.The governor could cause this type of problem, but generally they're pretty bullet proof. Unless someones has messed with yours, I'd bet the problem is elsewhere.

 

[Dave Ullrich]

Throttle Problems

I has almost the same problem with my Universal 5411 (11hp). I tried everything. Finally it turned out to be that the trottle was vibrating open and closed due to parts aging. A couple of washers fixed it up.