I thought this subject had been reviewed so many times that there was nothing else to know. However.....
Last year our 78hp Volvo was partially rebuilt by the Volvo agent in Hyeres. Not a happy experience, but we did end up with an engine performing as it should. With a clean bottom and prop the rev counter went up to 2800 with a top speed in calm water of about 8.4k, much the same as when the boat was launched 18 years ago. We are pretty rigorous about opening the throttle to max every 12 hours or so.
We put about 290 hours on the engine and then left the boat ashore till this month. I changed the oil and fuel filters. We have twin Racors before fuel reaches the engine.
Having launched, with a spotless bottom and Autoprop, we motored for about 12 hours at no more than 1900 revs.
Performance was perfect- up to 7.1k at 1800. I then opened the throttle but with the lever full ahead the revs would not exceed 2100. At 2000 revs we do 7.3k and at 2100 7.7k, what I would expect. But nothing above 2100.
More than that, on four occasions when I have tried full throttle the revs have fallen back suddenly to about 1500, on one occasion stopping the engine.
I should mention that the refit included a new turbo , injectors and exhaust elbow and the fuel pump was sent off to Bosch who confirmed that it was fine
Diving on the prop shows that it is still spotless.
My thoughts are that there must be a fuel shortage when I open the throttle; that there is sufficient flow up to 2100 for the engine to perform correctly but above that there is fuel starvation. I have changed both the engine and the Racor filters again, in case some fuel bug had grown over the winter and blocked them. The ones I took off were spotless and the fuel they contained was also spotless.
Anyone got any thoughts ?
Ian and Judy, Pen Azen, SM 302, Korfos, Greece