Yanmar - Backfiring and smoking!

[Nodak7]

OK! Ok! I saw the recent posting on Yanmar's recommendation regarding keeping the transmission in neutral when sailing. This is not about that recommendation but it is related. I want to know if anyone else has had a similar experience with their engine? When we first started sailing our H33 I left it in neutral. The vibration and noise were bothersome but the part that really concerned me was when I went to start the engine it would backfire terribly and smoke up a storm (black smoke). I spoke with the deal and he said he had never heard of this happening before. The backfiring was so violent that I was afraid to try to repeat it for fear I would damage the engine. Since that time I have kept it in reverse as a result.

So my questions are......

1. Is something out of adjustment?
2. Am I dreaming?
3. Has anyone else ever experienced this?

 

[Bill Roosa]

More info please

how long does it backfire?
As a general rule, diesels will not backfire (fire into the intake manifold) unless there is a severe valve timing problem. Course this would not change no matter what gear you where in or started in.
Are you saying it is firing through the intake or the exhaust?

 

[Benny]

Yes its hard for diesels to backfire. The black smoke is an indication of incomplete combustion. I would check the alingment and play on the shifter linkage. Put the linkage through its paces and observe how the transmission lever reacts. It should easily move forward and backward reaching its limiting stops. The only plausible scenario that I can think for your malady is that somehow the forward gears are meshed or continue to be meshed even with the shifter in neutral. The prop turning the shaft in the water intermitently engages the clutch which makes the engine turn and ingest raw fuel into the cylinders. If you want to try the boat in the water, just pull the stop cable to shut off fuel and prevent black smoke and uneven running at startup. Let the transmission freewheel and have an observer watching the engine for turns. If I were you I would continue to look for the cause as whatever the cause of the problem may be it is still there and could be adversedly affecting the useful life of other parts. In any instance I would love to hear what ultimately turns out to be the cause.

 

[jtm]

As I was reading initial post I was thinking along the lines of what turned out to be Benny's post. I tend to agree - black smoke indicating incomplete combustion and perhaps you may not be formally clearing and staying out of gear. Accordingly you could then be ingesting fuel which isn't(incompletely) burnt until you kick the engine over - hence your black smoke. Like Benny says, Check to see that you cables at the tranny are moving properly but also check the area in the (Merriman) pedestal- under the compass - sometimes the cable stems below the levers are loose and the cable (not the sleeve ) flexes/bends before going into the sleeve- so you may not be in the gear you think you are be just looking at the(external) shifter lever/ear.

Years ago I found that loosey-goosy stem mountings( the plastic lever housing that the stand off cable stems were mounted to- was cracking) were causing my cables to bend/bow rather than go into a stiffy(needed cleaning/lubing) sleeve and the throttle cable broke(metal fatigue) before it entered the throttle sleeve. But the cracked lever housing and loose stems were evident on both shifter and throttle levers.

Just another thought where to look and why.

 

[Nodak7]

Benny,

That was the first thing I thought of. Even though the engine was in neutral it was still continuing to turn over when I was moving forward under sail. Subsequently ingesting fuel.

She was brand new last season and I was very cautious about what I messed with but I think next season I will be more comfortable about getting into the works. She is on the trailer right now but I plan to check it as soon as she gets launched.

I was thinking that while it is on the trailer I should be able to put it in neutral, rotate the prop by hand and see if there is resistance. Correct?