'68 318 runs rough after revving.

[DavidWymore]

I know my timing chain is pretty slack per this test.

http://www.misterfixit.com/chanslop.htm


Carb is good (or maybe needs a dashpot?), GM HEI ingnition, runs decent except if I rev it and drop the throttle shut, it burbles pretty bad, bogs down, and the vacuum gauge flicks all over a few inches for about 30-60 seconds. I can't tell if it's going rich or lean. Timing doesn't go nuts per timing light. Think it's the chain? If I gradually close the throttle, it doesn't misbehave.

[olypopper]

Sure sounds like a carb issue to me.........what carb do you have installed?

[DavidWymore]

BBD, freshly rebuilt by a guy that's been doing carbs since the 60's. I've seen everything from top fuel to old British sports car to trophy truck carbs in his shop. He says it's likely timing chain and valve springs/lifters.

[olypopper]

Cams not flat is it?

[DavidWymore]

Runs good off idle to 4500 RPM, then valve float...he said they shouldn't float 'til 5000, so the springs are probably weak.

[nytemuvr]

Runs good off idle to 4500 RPM, then valve float...he said they shouldn't float 'til 5000, so the springs are probably weak.

And the timing chain after 45+ years or your missing a tooth of the cam gear, seen that many times. Nylon cam gears suck. Get a double chain timing set.