I have searched through many topics on here but still I?m having this problem. I have twin 250hp Yamaha ox66 engines that were stalling at idle. The problem had started after this past winter when work was done. May or may not be related but I needed the basics done LP pumps, VST, new thermostats ect? . Mechanic can?t find anything wrong. They run great and are burning less fuel after work was done. Engines will start fine, idle great for 5-10 min then stall. At the beginning of my problem they would both stall out no alarm except the constant beeping letting you know the engine has shut down. The engines are each running off their own tank. I can also switch them over to a 3rd main tank and the problem is still the same.
It think I have fixed the problem with one engine (it hasn't stalled the last time running it) but I am still having it on another. Once I give it some throttle it will run perfectly. Full RPM range up to 5500. It has never stalled out above 1500rpm. Once it stalls it will usually start right up, sometimes it will turn over and stall again. Funny thing is when it does that it will keep stalling unless I put it in neutral and give it some throttle (1500-2000rpm) and then it will run fine. When it stalls the primer bulb has fuel in it and so does the VST. One time it stalled out and would not start back up. Let it sit for a day then it would start and then stall. I also have noticed that on the flowscan it will lose GPH and goes to 0 useually before it stalls. Flowscan does work correctly.
This is what I have done.
1) Replaced LP pumps (also checked for bad diaphragms and they are good)
2) Cleaned O2 sensors
3) Cleaned VST
4) New fuel bulbs
5) Drained gas tanks and put fresh fuel in. (incase of water)
6) Cleaned spark plugs ( replaced about 40hrs ago, should I put new ones on?)
7) New water separator filters 10 micron
8) Mechanic tested fuel pressure and it was the correct psi (35 psi I believe was correct)
I ran it over to my mechanic last week in the water about 6 miles. One engine stalled whil idling but then started up. Couldn?t get it to stall again he couldn?t find anything wrong.
I am not really sure what to do next. Any ideas or thoughts?
It think I have fixed the problem with one engine (it hasn't stalled the last time running it) but I am still having it on another. Once I give it some throttle it will run perfectly. Full RPM range up to 5500. It has never stalled out above 1500rpm. Once it stalls it will usually start right up, sometimes it will turn over and stall again. Funny thing is when it does that it will keep stalling unless I put it in neutral and give it some throttle (1500-2000rpm) and then it will run fine. When it stalls the primer bulb has fuel in it and so does the VST. One time it stalled out and would not start back up. Let it sit for a day then it would start and then stall. I also have noticed that on the flowscan it will lose GPH and goes to 0 useually before it stalls. Flowscan does work correctly.
This is what I have done.
1) Replaced LP pumps (also checked for bad diaphragms and they are good)
2) Cleaned O2 sensors
3) Cleaned VST
4) New fuel bulbs
5) Drained gas tanks and put fresh fuel in. (incase of water)
6) Cleaned spark plugs ( replaced about 40hrs ago, should I put new ones on?)
7) New water separator filters 10 micron
8) Mechanic tested fuel pressure and it was the correct psi (35 psi I believe was correct)
I ran it over to my mechanic last week in the water about 6 miles. One engine stalled whil idling but then started up. Couldn?t get it to stall again he couldn?t find anything wrong.
I am not really sure what to do next. Any ideas or thoughts?