Jwoos
I have exactly the same problem as what you have. See my post here:
http://www.peachparts.com/shopforum/showthread.php?t=153830
My engine is I think the same family as your engine. I have a 605 engine. I think you have a 606.
I have still not solved my problem and will be checking again for leaks although I did not find any.
I was suspecting the car starting on 2nd Gear and when on an incline could not downshift to 1st.
Another thing I though about is to try to put a bottle of diesel right before the IP and run the car uphill. This will isolate fuel line problems.
Just my 2 cents. Will keep watch on your thread. Hope you fix it!
Francis