J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Yanmar

Hi recently made some "improvements" to my fuel system and had had some engine adjustments
When I went out last night I felt the Yamnar was missing power (it could have been the headwind and chop)

What should the RPM be at full throttle?

_)
Taras

Taras - the power, torque and fuel consumption curves from the Yanmar service manual are attached. You can see that torque and fuel consumption are pretty flat from 2400 to 3400 RPM. What these curves don't account for is the performance of the 2 blade Martec prop. I find that the "sweet spot" for best fuel efficiency and speed is about 2400 rpm. After that, the fuel consumption increases exponentially with small increases in speed. I'd find the RPM closest to 2400 where you don't have vibration from engine/drive train and use that. You can always increase the RPM for time when you really need the power, but no need burning excess fuel and placing excessive wear on the engine otherwise.

Vee Jay runs about a half hour to get from Naples City Dock to the Gulf ... interestingly we run most of time around 2400 which seems to be the smoothest ... and that gives us a bit over 5kts. there are definite rpm that don't sound "right" so we sort of tune around them.

Needless to say backing with the Martec against a strong wind or current can be interesting and full 3200 sometimes is not impressive.

vic

I have been noticing that my 2gm sound more like a single piston engine at low speeds. Has any one else noticed this. All the guys at the club have different opinions and before I call my mechanic buddy to help check it out I wonder if you all have any ideas. I am not the best engine guy.

On a separate note, I have noticed that my engine does well at 2200 rpms, and 2800 rpms but everything in between I feel like she is running rough and vibrates alot. I had the prop reconditioned and my C-bearing has no play in it, but in that mid range it is rough! Thought?

Canaan Leonard
Velocity Girl
#278

Check out the injectors and make sure the tips are clean. If you can take them to a diesel shop, they can do a "pop test" to make sure they spray atomized diesel fuel. Make sure you mark which injector goes with each cylinder.

If the injectors are ok, you may have to get the high pressure fuel pump checked to make sure each pump output is discharging the right amount of fuel at lower RPM. I had Mack Boring rebuild the pump last year and it helped a rough idle problem.