vti - With the larger idle gap you find yourself setting the LSN very rich in order to get the idle speed correct. In effect you are flooding or loading up the engine to keep the idle where you think it should be (basically setting the idle speed using the LSN and not the idle screw). In order to get the motor running what appears to be normal, you must have quite a lean HSN, to restrict the flow of fuel to the LSN (because the LSN is set way too rich). With a full tank this situation is not great but it works and the motor will run OK but not to itīs full potential. However, when the tank level and fuel pressure drops you canīt get enough fuel pushed through the HSN at near to or WOT because you have the HSN closed off too much, hence your lean bog after a few minutes running.
Another tell tale sign of an incorrect idle gap and compensating rich LSN is your motor holding onto revs when jumping.