[C320-list] Black smoke with 3GM30F

[dprudden]

Joe,
Everything I have read on the 3GM30F says to run the engine at around 2900 rpm. That's about 85% of max, which shouldn't be maintained for any length of time. There are plenty of others on this list that know a lot more than I on the engine, but that's what my research has found and a mechanic has verified.

David Prudden
#787

Sent from my iPhone

> On Aug 17, 2014, at 4:12 PM, JJ Morrison <sail-ability at sympatico.ca> wrote:
> 
> Could be your exhaust elbow has carboned up. Exhaust restriction often results in the symptoms you describe.CheersJohnM1999#574
> 
>> From: jtamucci at comcast.net
>> To: c320-list at lists.catalina320.com
>> Date: Sun, 17 Aug 2014 15:07:01 -0400
>> Subject: [C320-list] Black smoke with 3GM30F
>> 
>> Most of this season, the boat has been sitting on the mooring with not much
>> sailing or motoring.  In fact I still have the same tank of diesel I put in
>> last October 2013.  I also have a 3 blade Martec feathering  prop.  At the
>> beginning of the season, the boat ran great and I could get up to 7 knts at
>> 3400 RPM and no smoke at all, so the prop pitch seemed perfect.
>> 
>> Recently I noticed a fuel leak from the secondary filter so I bought a new O
>> ring but the leak around the cap continued and when I tried to screw it ona
>> 3rd time I lost the prime and even after bleeding the secondary could not
>> get the engine to start.  I had the yard mechanic fix it and they had to
>> bleed the injectors. 
>> 
>> 
>> 
>> I went on vacation for a couple weeks and same back. Now the engine starts
>> fine and will freely rev up to 3600 RPM in neutral.  When I put it in
>> forward however and give it some throttle, very little response and black
>> smoke comes out the exhaust.  Max RPM was 2000 with lots of black smoke and
>> soot.  It works much better in reverse but still some black smoke.  So it's
>> a classic overload problem due to a fouled prop or drivetrain?
>> 
>> 
>> 
>> So I dive on the prop but very little fouling but I scrap it clean anyway.
>> The haul is also clean. Same problem.  So I go down and repitch the prop a
>> couple times (it has adjustment screw).  The 1st time I repitched, the smoke
>> went away but I could only get up to 4.9 knts at max RPM of 3100.   After a
>> couple more adjustments I can get up to 3000 RPM and 6 knts before it starts
>> smoking at full throttle which gives me 3100 RPM.  The shaft spins easily by
>> hand turning at the engine, and the prop seems to be feathering fine.  The
>> engine is not overheating either, and very little vibration in the
>> drivetrain.  So I was able to improve things but still not like before.
>> 
>> 
>> 
>> So after all that, my question to you is, is it still an driveshaft overload
>> problem, or could it be an engine problem?  Could the mechanic have screwed
>> anything up by bleeding the injectors?
>> 
>> 
>> 
>> 
>> 
>> Joe Tamucci #619
>