Thread: vacuum advance
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Old 02-17-2000, 03:52 PM
Registered User
Join Date: Oct 1999
Location: Tulsa, OK USA
Posts: 139
Yes, I bought the balancer from JC Whitney. It is a good unit HOWEVER you still need to make an adapter. I made mine from a Tupperware bowl and it works fine. JC did not list any adaptors for the unit when I got it (approx 3 or so years ago). I forgot to mention if you do surface the top plate then you should also mill/file some material from the BOTTOM of the choke plate. After you surface the top plate it is possible that it will now set low enough due to material removal that the choke plate will catch on the primary venturi spray bar. Also, when you balance your carbs based on idle speed (I have an automatic so I set mine to 900 rpm) THEN go back and set the idle adjustment screws. Once done, you may or may not have to rebalance to speed again. Also, when you are balancing the carbs make sure you disconnect the carb-to-carb linkage rod. I didn't do this once (well, it was late on a Sunday) and couldn't figure out why I was just making matters worse. Your Haynes manual has the jet and air/corrector information you might want to check when you take the carb apart.

ONE ERROR in my earlier post was when I referenced the air corrector "4S", I should have said the Emulsion tube UNDER the air correctors - sorry. I believe yours should read "4S" for Primary and "4N" for Secondary.
You might also have a "5N" in the Secondary and that will not hurt anything. Check your jet sizes vs the Haynes manual when you have the carb apart.

You might want to pull a spark plug, actually numbers 1 and 6 and see if they are covered with soot. If they are, then you obviously have a super rich condition and that will point to other carb problems (high float, internal leak, stuck or improper setting on the vent valve(s) etc. Probably you don't have this as you would see a lot of black smoke.

Good Luck.


PS. (edit) Forgot to mention, before you go out and buy a wrench to cut in half, make sure of your carb mounting nut sizes. Some are 12mm and some are 13mm. Mine are 13mm. I think the originals were 12mm and replacements (as mine are) are 13mm and DONT OVERTIGHTEN them or you will crack the insulating blocks (don't ask about how I know that).

Dan Taylor/ Tulsa, OK MBCA '71 250C/'81 300TD-T

[This message has been edited by DANTRCAV (edited 02-17-2000).]
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