8 hp yanmar

[Denile]

Looking for a little incite on my 8 hp Yanmar diesel. I recently rebuilt the head and changed the head gasket on my inboard. Got it up and running with little issues. my only problem now is when I give it full throttle I get large amount of black fuel (or exhaust) coming out the exhaust pipe. The boat seems to run fine at half throttle but I think it should have just a bit more speed.
I did notice this prior to doing the head job, in fact it was worse than it is now.
any feed back would be most appreciate.

 

[Rick2413]

Noticed you haven't received any input yet and thought I'd make an attempt. The reason for black smoke could be a wide range of causes. Common problems are an overly carbon blocked exhaust mixing elbow(although I suspect you checked that when you had the head off). Another possibility is a wrong size propeller. This in combination of running the engine above the RPM range of your motor or prop is oversized can also cause black smoke. Another possibility is the shims on your high pressure pump are not correct and too much fuel is being injected and not burnt. Do you have a tachometer set up on your control panel? Personally, the two places I would confirm first is that your operating in the proper RPM range and the mixing elbow is not clogged. Hopefully others will jump in here.

 

[Jalepeno]

* Can you give us a bit more information *

Is it safe to assume you have a Yanmar YSB/YSE/YSM-8 with the typical 2:1 gear ratio?
Is it safe to assume you have a CAL 2-25 when your profile boat type is "2 25"?
What propeller diameter and pitch do you have?
What is your maximum no-load (neutral) motor RPM? The YS_8 series governor should limit it to 3400 RPM.
What is your maximum loaded motor RPM? It should be 3200 RPM.

I believe that black smoke is usually an indication of motor overloading. Did you perform the motor work to try to solve the black smoke problem?

If you cannot reach 3200 RPM under full load your propeller is probably too large and/or has too much pitch. Most sail boats with a displacement of around 5000 lb, 22 ft LWL, 8 HP nominal and a propeller speed of 1500 RPM use a 12" diameter propeller with 7" pitch.

I have an YSM12 in my CAL 2-25 with a Campbell Sailor CS3LH12x7x1 propeller. The boat originally came with a CS3LH13x9x1 that could not get to full load speed, caused black smoke and motor overheating. It is usually not expensive to reduce a propeller diameter and/or adjust the pitch.

 

[Denile]

Thanks for the input , Ill try to answer the best I can, I purchased the boat only 6 months ago so I don,t have a lot of info.
Is it safe to assume you have a Yanmar YSB/YSE/YSM-8 with the typical 2:1 gear ratio?
YSM 8 unsure of the gear ratio
Is it safe to assume you have a CAL 2-25 when your profile boat type is "2 25"?
I have a Yamaha 25 1978
What propeller diameter and pitch do you have?
unknown but I have no reason to beleave it is any different than the stock one
What is your maximum no-load (neutral) motor RPM? The YS_8 series governor should limit it to 3400 RPM.
I dont have a tach so it is hard to tell.
What is your maximum loaded motor RPM? It should be 3200 RPM.
unknown
I believe that black smoke is usually an indication of motor overloading. Did you perform the motor work to try to solve the black smoke problem?
no, I blew a head gasket so I pulled the head, cleaned and lapped the valves, cleaned the exhaust elbow(that was not very dirty) and put her back together.. A prety easy job for the most part.

If you cannot reach 3200 RPM under full load your propeller is probably too large and/or has too much pitch. Most sail boats with a displacement of around 5000 lb, 22 ft LWL, 8 HP nominal and a propeller speed of 1500 RPM use a 12" diameter propeller with 7" pitch.
I'll have to wait until I pull her out to check the pitch..

I have an YSM12 in my CAL 2-25 with a Campbell Sailor CS3LH12x7x1 propeller. The boat originally came with a CS3LH13x9x1 that could not get to full load speed, caused black smoke and motor overheating. It is usually not expensive to reduce a propeller diameter and/or adjust the pitch.
Thanks for all the info. I never checked the pump timing, do you think this may be a problem?

 

[Denile]

Noticed you haven't received any input yet and thought I'd make an attempt. The reason for black smoke could be a wide range of causes. Common problems are an overly carbon blocked exhaust mixing elbow(although I suspect you checked that when you had the head off). Another possibility is a wrong size propeller. This in combination of running the engine above the RPM range of your motor or prop is oversized can also cause black smoke. Another possibility is the shims on your high pressure pump are not correct and too much fuel is being injected and not burnt. Do you have a tachometer set up on your control panel? Personally, the two places I would confirm first is that your operating in the proper RPM range and the mixing elbow is not clogged. Hopefully others will jump in here.

I will look into getting a Tach, I hear you can get one that runs of the alternator. here is a dumb question, is there any way of checking the pitch without lifting the boat out of the water.

 

[Jalepeno]

I'm familiar with the Yamaha 25, great sailboat. Similar size boat except your LWL is shorter and your YSM-8 is mounted your under the V-berth. I would expect your Yanmar YSM8 would be set up similar to my YSM-12. Just checked my copy of "Marine Diesel Engines" by Nigel Calder and he says that black smoke can be caused by:
- Dirty fuel
- Defective injector
- Injector timing advanced or retarded
- Too much fuel injected
- Plugged air filter (a YSM-8 does not have an air filter)
- Plugged exhaust/kink in exhaust hose (you have a very long exhaust hose)
- Engine overload due to wrong propeller, rope in propeller or dirty hull

I know it cost money for a lift, but you should check your propeller. Don't assume the previous owner had the correct size. It should have the diameter and pitch stamped on it. Good luck, if the propeller is a three blade 12" diameter x 7" pitch or a two blade 12" diameter x 8" pitch, it should be OK. But it look OK then maybe it is time to get an opinion from a Yanmar mechanic.

 

[Jalepeno]

I just ordered a "Tiny-Tach". I'll give you a report in a week or so.
http://www.tinytach.com/tinytach/diesel.php

 

[Ameseys]

I'd check the overloading things first - it's the cheapest and easiest to rule out. Does the shaft turn freely - is the propellor fouled?. Is the bottom reallly dirty? It could be either of these. At full throttle, are you just making a wake?

That said, I rarely run at full throttle. It's too noisy and uncomfortable. I cruise slower and make about 5 knots with my Yamaha 25. You can't really get too much more that that out of the hull. Honestly, my ysm-8 is well-matched for the boat. Wide open just makes smoke and a wake.

 

[Nick H]

Agree - I get the same discharge on my Yanmar 10 Hp when my prop is covered with barnacles. Grab a snorkel and a knife and cut them off.

 

[Syntonos]

Ameseys is on the mark -- my Y25 with YSMB will max out at 5 knot (hull speed). Any more rpm and your just blowing smoke! Relax and enjoy the ride! Ya won't get there fast but you've got a 100+ mile range on a few bucks of diesel. My biggist problem is using up the fuel !!

Let us Know how you like the Tiny Tac ---- We use them where I work for small gas engines and they work great! I'm sure you'll be happy with the diesel model.

Lyn
Long Beach Ca.