We did the dockside testing and the first sea trial for the new BD1005 in our Bristol34. The good news is that the engine is quiet, smooth, and powerful, just as I had expected. We have a couple of minor problems though:
1. The mechanic had to set the idle at a tick over 1000 RPM. Any lower than that, and the engine ran very rough. Is this normal?
2. The engine ran fine at the dock, but when we went out for the first sea trial, we experienced what seemed to be fuel starvation, particularly at lower speeds (1200-1500 RPM). I could usually keep it running by goosing the throttle a little; it did quit once, but started right up again. It continues to run fine at any speed at the dock. The filters and the fuel are clean.
Page 29 of the engine manual says that an electric fuel pump must be fitted if the suction head is more than .25 m. The level of fuel in the tank may be close to that point now. Would that cause the problem I described? Since the fuel tank is about 18 in. deep, it looks like an electric pump will be required anyway. I read somewhere that a drawing is available showing the installation of an ignition-actuated pump. Is this available for download?
3. We reached hull speed at 3200 RPM at which point the engine topped out. I suspect that the prop is a little over-pitched.
I will deal with your issues in reverse order. 1) You are correct in assuming that you are overpropped. This doesn't appear severe and I think that you will be fine if you have your prop re-pitched at your next haul out. 2) I suspect that you may be sucking a little air into the system at one of the hose clamp joints (also mabye at the primary filter). As the engine has a self bleeding fuel system it will pass a bit of air without quitting like the older diesels. This however can make it a bit more difficult to spot the air leak than it used to be on the older systems.
The other things to check are that your tank breather is clear and that the tank pick up is not restricted with a check valve. I have had problems with check valves before. Basically on small demand (like at idle) they can starve the engine for fuel as the lift pump is working hard to overcome the resistance so you will get less fuel flow. At higher demand you generally dont have a problem. I suggest that if you do have a check valve in the system that you discard it.
3) I believe that the rough running at idle is the result of poor fuel supply and will be cured when 2 above is resolved. These engines generally idle very smoothly at 900 to 940RPM.
Please let me know how you get on. Regards, Stanley
Thanks for your thoughts. I'll check the vent line and go over the fuel supply line again.
What about the matter of the suction head? The manual says that the lift pump has a limit of .25m (between 9-10 inches); my fuel tank is about 18 inches deep. The tank is a little over 2/3 full, giving a total lift (including the fitting on top) of about 7 inches. I'll fill it up tomorrow. For the long term, though, should I plan on installing an electric pump?
In spite of these minor problems, I want to emphasize how pleased we are with the engine. When we were under way, it was very smooth, quiet, and powerful. In fact, when we were on our way back to the dock, my wife, who was foreward, kept asking, "Is the engine still running?" She was amazed: when our old engine was running, we could not communicate by voice for more than the length of the cockpit.
I think we finally solved the problem. The new fuel shutoff valve was apparently defective. We completed the sea trail on Saturday--it was great! Sorry to take so long to get back to you.
