port engine on twin 150's surging

[Popeye55]

2000 twin ox66 150's hpdi: the engines run great for the first hour or so then the port engine, when operating at 2000> rpms drops rapidly to apx 1800 rpm then again rapidly increases to 2000>. this sequence is repeated in very fast movements until i pull back on the throttle. It operates well at that point on if I keep it at under 2000 rpm's. Engine oil tank is at normal level, new fuel filters (as it is only the port engine and a common fuel supply I believe fuel is not at issue here). There is no alarm given when this happens, both engines seem to be at normal operating temperature.

Thoughts?

Thanks.

 

[TwoRivers]

Re: port engine on twin 150's surging

Spun prop?

 

[Capt Ken]

Re: port engine on twin 150's surging

Check the low pressure fuel pumps behind the VST tank.