Experience Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.
Organizations Associate member SAE
EAA member
Publications Import Car magazine
Education/Credentials ASE Master Auto with L-1 certification up to 2000
Question QUESTION: The diaphragm at the distributor must be ruptured and will not hold any vacuum. Consequently the engine stumbles on acceleration until the centrifugal catches up. While the unit is held on by 2 screws, I can't find one with any of the suppliers I have looked at. Do you have any idea where I can find one or improve the centrifugal capability?
ANSWER: Hi Frank,
The vacuum advance and centrifugal advance work under different circumstances so one can't take the place of the other. You may be able to set the timing so as to be a compromise. Have you tried Moss Motors, British Victoria, The Roadster Factory or Engel Imports? One of these should have an advance unit. I think your car has a vacuum retard unit not an advance unit. What is the number on the dist? and is your unit mounted on a box on the side of the dist? or is it mounted directly on the dist?
If it is a retard unit it is easier to adjust the timing to counter the missing unit.
To adjust the springs in the centrifugal advance to counter act the loss of a vacuum retard unit can be done but it would difficult to do without the use of a distributor machine. If you have a local race car shop they may be able to help. Let me know,
Howard
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QUESTION: I do have a vac retard unit. Vic British doesn't sell the EGR valves and I will look elsewhere if necessary. I checked my EGR valve with a propane torch and I do not think is is leading vacuum. If I can eliminate it's function with timing it would seem to make sense to do so.
I am presently trying to smooth out the idle and that was what made me realize that the valve was not working. I have tried to adjust the carb to the extent possible and while the car runs good I would like to smooth it out a little more.
Your thoughts are appreciated.
Frank
ANSWER: Frank, you can't eliminate an EGR with timing. An EGR valve is Exhaust Gas Recirculation valve. It has nothing to do with timing, it puts exhaust gas into the intake to dilute the air/fuel mixture in the combustion chamber to cut down on NOX (Nitrogen burning due to an over heated combustion chamber when the factory leaned out the mixture in an attempt to clean up CO and HC) a carboned up EGR valve will cause a intake leak that can make an engine idle poorly though.
I know that sounds like a monkey puzzle and it is.
The sequence of events are, the manufacture tried to clean up emissions by leaning out the fuel mixture. This however over heated the combustion chamber which made the Nitrogen in the air start to burn resulting in NOX, a more poisonous gas than the ones they were trying to clean (CO & HC). To try to then clean up the NOX, they recirculated some of the exhaust gas into the combustion chamber to dilute the fuel/air mixture to cool it down a little thus preventing the burning of the Nitrogen.
Howard
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QUESTION: Other than the more obvious effects of a carbon created vacuum leak, what would be the effects of an EGR valve that is closed and does not open? I would think that the gasses reburned through the valve would be leaner.
Thx
Answer If you have no EGR the combustion chamber temperature would be high and can cause detonation which causes engine damage. Even without detonation the higher combustion temperature would produce NOX and effect the exhaust valve temperature. A slightly richer mixture would solve all of this until you can locate a new EGR valve.
Howard
