Quote:
Originally Posted by mercmad6.3
BTW, the vacuum is the governor for the pump ,it doesn't actuate the rack which is why they will still start but smoke really badly . The rack goes to full fuel but because the throttle plate doesn't open ,there isn't sufficient air..rich running is the result.
|
Quote:
Originally Posted by billhard
Our understanding of how the IP on 616 in the w115 chassis functions are different, and I am not sure who is correct. To my knowledge the fuel flow for IP's on the 115 is pneumatically controlled (a vacuum line from the rear of the IP to the intake manifold behind a butterfly valve) and the mechanical linkage act only as a damper.
|
The vacuum for the governor of the pump is not created by a vacuum behind the butterfly valve, but by a venturi under the butterfly valve. The valve controls the amount of air flowing through the venturi. Also an increase in the speed of the engine will increase the air flow through the venturi.
The vacuum works upon the membrane. The membrane connects to the rack, so more vacuum and the rack moves towards the stop position. There is also a spring inside the governor that pushes on the membrane and so, if there is no vacuum, the membrane moves the rack to the full load position.
The rod to the IP controls the auxiliary mechanical governor, i.e. the poppet cam. That steadies the rpm at idle and at low speeds, otherwise the engine would be "sawing".
In the picture below you can see it. Nr. 8 is the rack, nr. 10 the membrane, nr. 13 is the spring, nr. 15 is the poppet cam.
If the governor housing is not air tight, more vacuum is needed for a certain engine speed. More vacuum is created by keeping the butterfly valve more closed and that will cause a rich mixture and smoke.
You did replace the membrane, but did you check whether the governor housing is air tight? It can also leak from the axle of the poppet cam (and it frequently does).