914 idle rpm surge.
in 912 / 914 Technical Questions
6 years ago
Hello Gents.
I have this 4 year old 914UL with 180 hours only and looking brand new witch has begun to surge, Hunt or osscilate in idle.
I made 2 videos of the behavior if anyone would like to see them.
The engine oscillates only in idle.
Idle is set to approx 1800 with about -0.5bar on the Syncro dials and it is dropping to 16-1500 and pressure increases to -0.4 bar on the Syncro dials for about 15-20 seconds with rough running and then it raises back up and stabilize smooth idle.
After about 30-60 sec it drops again and it continues like this.
1 or two fuel pump on, 1 or the other or both ignition systems on doesn't change anything.
I have tried to clamp the cross over tube but then the rpm drop becomes permanent and even more rough running. Added throttle and back wont just raises it again. The clamp must be removed and it needs 25-3000 for 10-15 sec to stabilize again.
Maybe the rough running with the clamp on causes the floats to bounce and flood the chamber because Sometimes fuel is coming from the chamber vents ones the low rpm rough running is going on. I'm thinking this is the result of the rough running and perhaps not anything to do with the fault. Maybe.
I have looked for components that could leak, like different big and small hoses, manifold, MAP indicator ect. None seems to have any damage.
I have suspected the map indicator as this is a new installation but this was disconnected and plugged on the engine.
Carb Syncro checked ok.
Idle jets checked ok.
Idle mixture checked 1,5 turn out ok.
We have visually checked the floats for damage, no smoking gun there. I have not weighed them yet.
I have also been thinking about Carb ice but I doubt it can be that even the ambient temperature is just below freezing.
The map increases when the rpm drop occurs.
The waste gate actuator doesn't move when it happens.
Can it be a leaking carb diaphragm?
Thinking its not.
Looking at the video it seems to start on the left carb side.?? and then pulls the other with it.
We will replace the spark plugs and check slipper clutch friction and ignition pickup gap though I don't think those are the cause..
I will check the fuel pressure if above inspections doesn't show anything.
Any other ideas is much appreciated?
/Brian
I have this 4 year old 914UL with 180 hours only and looking brand new witch has begun to surge, Hunt or osscilate in idle.
I made 2 videos of the behavior if anyone would like to see them.
The engine oscillates only in idle.
Idle is set to approx 1800 with about -0.5bar on the Syncro dials and it is dropping to 16-1500 and pressure increases to -0.4 bar on the Syncro dials for about 15-20 seconds with rough running and then it raises back up and stabilize smooth idle.
After about 30-60 sec it drops again and it continues like this.
1 or two fuel pump on, 1 or the other or both ignition systems on doesn't change anything.
I have tried to clamp the cross over tube but then the rpm drop becomes permanent and even more rough running. Added throttle and back wont just raises it again. The clamp must be removed and it needs 25-3000 for 10-15 sec to stabilize again.
Maybe the rough running with the clamp on causes the floats to bounce and flood the chamber because Sometimes fuel is coming from the chamber vents ones the low rpm rough running is going on. I'm thinking this is the result of the rough running and perhaps not anything to do with the fault. Maybe.
I have looked for components that could leak, like different big and small hoses, manifold, MAP indicator ect. None seems to have any damage.
I have suspected the map indicator as this is a new installation but this was disconnected and plugged on the engine.
Carb Syncro checked ok.
Idle jets checked ok.
Idle mixture checked 1,5 turn out ok.
We have visually checked the floats for damage, no smoking gun there. I have not weighed them yet.
I have also been thinking about Carb ice but I doubt it can be that even the ambient temperature is just below freezing.
The map increases when the rpm drop occurs.
The waste gate actuator doesn't move when it happens.
Can it be a leaking carb diaphragm?
Thinking its not.
Looking at the video it seems to start on the left carb side.?? and then pulls the other with it.
We will replace the spark plugs and check slipper clutch friction and ignition pickup gap though I don't think those are the cause..
I will check the fuel pressure if above inspections doesn't show anything.
Any other ideas is much appreciated?
/Brian
