Originally Posted by barry123400

In theory you should see no air leaving the primary plastic filter. As I said in theory it makes sense. Any bubbles traversing the plastic filter should be eliminated first I think.

It is a quantity of air issue I imagine with no established guidelines of how much if any is permitted. The same type of appearance by comparison to the two fourty is a reasonable solution to shoot for. There should be no difference in appearance as you rev either engine to half throttle in that little filter.

Also you are describing a hunting condition in my opinon rather than a roughness? If just a rough constant condition it will be easier to address. A dose of cleaner through the injection pump might be considered after the air is eliminated or reduced. Something might be sticking a little as the rack is govenor controlled I expect if hunting is involved.

Also examine your fuel pump base pressure if you have not already. A temporary test is to clamp off the return line for a minute and see if the hunting ceases. Or roughness declines.

There have been no reports of hunting with low base pressure to my knowledge. I am always on the lookout for abnormal symptoms remember. Rougher idle than is possible is caused by very low base pressure though.

Maybe a combination of low base pressure and some air could be impacting things. I have to wonder if any fuel is overcoming the relief valve and if that fuel shows evidence of air containment in a container with the end of a hose submerged. A few simple things to check that may or may not improve things. They should be checked anyways anytime strange idle conditions exist.

There have not been many posts on hunting posted to my knowlwdge yet still a few if I remember that were not resolved I believe. We did not have as good an undertanding back then though.

Or to look at this generally even if the problem does not go away with getting those things in good shape. The car should actually run better as it hunts. The only other upside then? You will have a firm grasp of what is not causing the problem.

The only mandatory thing that is indicated is the foaming in the primary filter has to be stopped. Your other car would do it as well if it were normal remember. The fuel supply systems are identical as far as I am aware.