My Z as of late sounds like it is running under water. I rebuilt a '81 L28 for my '73 in 2000, SU carbs, headers. Seemed to run fine. I knew it was running rich due to the black crap that seems to collect on the tailpipe (and about every month or so I need to clean my left taillight of that black frost). The engine has about 7000 on her.

While driving home last night, was running fine. Al of a sudden the engine tone went down an octive, as if it was running under water. My guess is something fuel related. Maybe timing. Is it possible it just worked its way that far out of timing. My gas milage has been sucking lately anyway, Last carb adjust on the SUs was mid 2000. Any other thoughts?

Hi sounds like you have a engine out of tune try a tune up, but first check the plugs to see if one or more are black and sooty, this may show a problem with one cylinder, I would recheck the timming and set the carbs up again and see if this helps,May be the dizzy has moved changing the timming.

Hope this helps.

Well I will certainly try it. It was kinda weird though, was driving just fine then it was like it was underwater.