Backfiring while driving at high speeds ???

[not_sure]

My car has been running great, I drive it all around town and it runs fine all the way through the rpm range( about 5500 to 6000). Problem is when Im on the freeway doing 75+ its making a popping noise through what sounds like the carbs, Im not sure of course because that would be hard to check at 75 mph. Is this a timming issue maybe, Im just not sure where to look first since it runs great at lower speeds. Any thoughts?

[Superman]

It might be a timing issue, but intake popping is normally assoicated with a overly lean mixture. If your spark plug electrodes look whitish, I'd suspect a fuel mixture problem or misadjustment.

Cars that are running lean also commonly do a little sublte surging during normal operation.

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'83 SC

[not_sure]

Yeah, the car use to surge somewhat, I was told by a wrench the there was an air leak somewhere in the carbs that was causing that, after a bottle of techron that problem has since passed. I always wonder about the timing since I do not have a vacume line attached to the distributor. I dont do a lot of freeway driving, but I would just like to fix all the problems none the less.