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MG MGB Technical - exhaust emission and ignition timing

I was wondering if ignition timing is related to the quality (smell) of the exhaust gas. My 74B has a pertronix igniter in the distributor and two new HIFs. Plugs electrodes have that brown deposit indicating proper mixture, but exhaust still smells very heavy. Will altering timing reduce the exhaust odor, and if so, should I advance or retard the timing? Thanks for your help.
WL Leong

Not really...unless the timing is well out. Should be running 15 degrees. Balancing those carbs properly will have more to do with your exhaust smells...and they aren't always that easy to set up even new.
Pete
P J KELLY

Retarding the timing will decrease emissions. At idle, over-advanced timing will make the exhaust smell rich. Cams hotter than stock won't idle as smoothly as a stock one and will cause a little more pungent exhaust.

Not related to your Pertronix, but either the vacuum or centrifugal advance can get hung up and mess with your timing. Make sure your distributor is clean and lubricated.

Also harmonic balancers come unglued, causing the timing mark to slip away from the correct spot. You might want to verify that the timing for TDC really is at TDC.

I'm told that in these days of unleaded gas and additives loaded by the refineries, reading plugs is less telling than it used to be.

As P J says, take a second look at the carbs, be sure they're balanced and then that the mixture is set correctly according to the "lift the pin" method.

If still in doubt, spend $15 to take it to a shop and have them put the sniffer in the tail pipe. That'll tell you for sure if you're running rich.

Best wishes,

Matt K.
Matt Kulka

This thread was discussed between 14/10/2003 and 15/10/2003

MG MGB Technical index

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