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  #21  
Old 11-12-2012
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Re: Why does my diesel not rev when in gear?

Reviving thread from the dead because I have same issue and found this thread to have lots of useful info.

Problem Statement: 1) Hard starting. Crank about 2-5 minutes. The engine will sound like it's trying to start, cranking sound will increase in pitch, engine slowly chugs to life and I can let off the starter. Once warm, engine starts right up again.

2) Idles fine. Revs up to max on tac with no load (and throws off alternator belt). Under load, I get a max of about 1500 RPM with boat speed on GPS of about 3.7 knots. I have either a light white or grey exhaust, can't tell which.

Additional info: A PO removed the fixed tank and installed bladder tank in locker. The feed from this tank includes an electric fuel pump which is switched on before starting (to overcome a faulty fuel pump elsewhere?)

I spent a lot of effort trying to get cooling water through the engine. The reverse gear water jacket was completely plugged up and required acid solution to get water flowing again. Although I eventually got a good water flow, the exhaust elbow could still be an issue as mentioned in thread.

So my todo list appears to be changing fuel filters, checking fuel quality, fuel flow, and exhaust problems.

Did I miss anything?
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  #22  
Old 11-12-2012
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Re: Why does my diesel not rev when in gear?

The first step is still the same : have you eliminated the cleanliness of the propellor and bottom as the cause of the low boat speed?

Secondly hard starting is often the glowplugs.
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  #23  
Old 11-12-2012
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Re: Why does my diesel not rev when in gear?

OBTW, I have the MD7A of the 13 hp flavor, not the 7B of the OP. There are no glow plugs on this engine.

Thanks for the reminder regarding fouled prop. I missed that on my todo. The boat was out of the water last winter and bottom painted this past spring. I'll still take a look though.
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Re: Why does my diesel not rev when in gear?

Oh and I did sail it for a few hours. It sailed fine which seems to eliminate the bottom, but not the prop.
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Re: Why does my diesel not rev when in gear?

While I've not solved everything completely it is working much better. Turns out there were several contributing issues and I've sorted most of them out.

The local mechanic noted that the exhaust manifold had a short distance of slightly upturned section before it sweeped down to the water muffler...this was apparenatly allowing condensation (with some rust from blackiron exhaust) to trickle back down into the engine thru the valves. The manifold was removed cut apart and rewelded to have the proper angle down...apparently this is a critical issue to keep spent exhaust water from getting back to your valves/engine.

The mechanic also noted the engine was idling too slow and increasing the idle to the proper RPM fixed the engine rev issue immediately.

I completely drained the tank and put in fresh fuel...the diesel in the bottom was quite reddish/brown and smelled bad.

There's apparently a small air leak in my fuel delivery system which given enough time (a week or so) will make the engine a bit difficult to start...thankfully cranking the engine eventually expells this air and when fuel hits it starts.

To clean up the valves/engine I added some Marvel Mystery Oil to both the fuel and the crankcase. After getting the engine started with this in it there was some nasty stuff coming from the exhaust that over a period of time cleared up. The engine gradually ran smoother as this ran thru it and it became easier to start (if this hadn't worked a valve job would be in order).

I still have the air leak issue so starting after setting a week still takes a bit until it flushes and the fuel hits...it more or less readily restarts throught the weekend.

Hope this helps...
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Re: Why does my diesel not rev when in gear?

Thanks for the followup....
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