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Ask Sail: Low Revs and Soot

I own a 1987 Catalina 27 with a Universal M18 diesel engine. I’ve had the boat for just over two years, but because the hour meter is broken, I don’t know how many hours are on the engine.

Andrew Gardner of Long Island, New York, asks:

I own a 1987 Catalina 27 with a Universal M18 diesel engine. I’ve had the boat for just over two years, but because the hour meter is broken, I don’t know how many hours are on the engine. The manual says maximum rpm is 3,200, but the most it will do out of gear is about 2,700 rpm (confirmed with a photo-sensor tachometer). It also stalls out below 1,000 rpm, and black soot accumulates on the transom.

I’ve replaced the injectors and fuel filters. I’ve changed the oil and oil filter several times. I’ve inspected the exhaust elbow and air intake for blockage. I’ve even tried feeding it fresh fuel from a jerry can, but I still can’t cure this. A compression test showed compression is right on spec. On the positive side, the engine starts right up and otherwise seems to run OK.

Nigel Calder Replies:

Does your engine have a decompression lever? If so, check to ensure that it is not holding a valve cracked open. Otherwise, this could be something as simple as the throttle not advancing the fuel rack on the injection pump far enough. Have someone work the throttle while you look at the engine end to see whatever lever or rod it is moving. Try pushing this farther by hand and see what happens.

But this will not address the stalling and the black smoke. Did these problems precede or follow the injector replacement? If the latter, I would suspect an injector problem. Finally, a sticking governor could explain things, but this requires more disassembly to check out.

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