Volvo Penta 7.4 Loping at Idle

I have a Volvo Penta 7.4 that is Loping at Idle. I found a crack in the block last summer so I had to have the engine rebuilt. My mechanic put the engine in last week and set the timing and everything was running great. Now after this past weekend it is running like this at idle. (Please see attached link)

http://www.youtube.com/watch?v=2JF1_N6dE98

To be fair 80% of the time it is running with a lope at idle and the other 20% running completly like it is supposed to run at idle. Once it is put in gear under load it runs great as well. I am not sure if it is a fuel supply issue or what. I am pretty new to this type of thing and not sure which way to turn. Please let me know of what questions you may have and I will try to answer them to the best my ability.

Thank so much for your help!

VOLVO PENTA 7.4GI PBYCCE
4110165296
3868781

Outdrive
DP-SM
4112049602
3868912

Re: Volvo Penta 7.4 Loping at Idle

Wow. More like surging than a lope. Mine was actually loping like it had a radical cam in it and it turned out to be the low pressure fuel pump. It was starving the engine of fuel but not enough to prevent it from idling. This caused a lopey sound at idle. Check your fuel pressure. Have your mechanic hook it up to a diagnostic machine too.