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Like the one post mentioned, and I mentioned last week, check the screen at the inlet to the scavenger pump. If that's ok, it's not too hard to pull the scavenger pump off the main pump housing. Two of the bolts on the back cover are larger than the rest, and these two hold it to the main pump. Once it's off, remove the rest of the smaller bolts and take the back cover off the scavenger pump. A few possibilities then to check for are: 1. The gears of the pump and the hex drive that drives them are held on the shafts by tiny rollpins. One of these may have sheared. 2. There's a small springloaded valve in the pump housing that may be stuck(Make sure you don't loose the spring when you pull the cover off the back of the scavenger pump). 3. This was the problem on my 650D- The pump is driven off of the end of the governor shaft inside the main pump. The end of the governor shaft is square, and there's a part that's rollpinned to the shaft of the scavenger pump that fits over the square end of the governor shaft. It looks about like a 1/4" drive socket and extension(sorry I'm not describing this real well but you'll be able to see what I mean once you have the scavenger pump off). Anyway, on mine, the square end of the governor shaft was rounded off. To fix it I took the whole main pump apart and welded up the rounded-off area then filed it until it was back to it's original square shape. I should note that I have a manual for the pump that helped me here. I was able to get a few seals from IH but had to make most all the paper gaskets myself. Hope this helps!
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