Loss of power Yanmar 4jh4-hte

Jun 20, 2016
Hunter 50 Hobart
We have a Hunter 50 just 3 years old and are sailing in Malaysia. Coming up the coast to Rebak Island we found that the engine would not rev over 1800 rpm under load and in neutrl it only revved to 2000rpm. We motored sailed most of the way but missed the extra speed we should have been able to do. At Rebak Island we have a very good Australian mechanic looking at the problem but even he is perplexed. Having surfed through lots of threads it does appear to be a problem many others have had with varying solutions. As it happens in neutral we eliminate the prop. The boat has been at Puteri Harbour in the marina idle for 6 months and we have only just returned from Australia. Our trip up the coast started alright but after the first 24 hours we noticed the problem when trying to avoid a ship. We pulled into shore and replaced the primary filter with no change. We decided to continue on. At Rebak we have tried fuel direct from a can, put a pump in the fuel line and checked and bled both filters. There is now bluish smoke once 2000rpm is reached. Throttle cable has been checked. No change in the revs. Next avenue will be check the injectors. Does anyone have any ideas?
Apr 11, 2016
San Juan 28 Comox
I had a similar issue with my Yanmar 2 YM15, it would only run up to 1800-2000 rpm even while sitting at the dock. We checked the fuel filters, fuel supply, and bled the system to no avail. The Yanmar mechanic had a feeling it was not injectors but rather some blockage in the exhaust manifold that causes this problem. Sure enough, after removing the units, they were checked and cleaning was tried but they basically fell apart inside.
Had to replace both elbows and the SS connector on exhaust and voila, problem solved.
So my recommedation is to check the exhaust elbows as well as this apparently is a common issue. Hope it all works out for you.