Bob,
Are you sure it is "popping" or is it "Backfiring"? There is a difference.
If it is popping it could be the result of an extreme "lean" condition under
load. Such as with fuel starvation of the main jets. If it is backfiring it
has unburnt fuel igniting in the intake or leaking into the intake through
an intake valve either due to changed valve timing, changed ignition timing
or a burnt valve. It is possible that the valves (rockers) were adjusted too
tight and may need to be re-adjusted (I agree with Bob Palmer here). I would
suggest the process of elimination starting with a compression test. Do this
correctly with all of the plugs out and the Carb pinned at WOT. If the all
seem within 10-15lbs you then need to do a leak down test. This is a test
that pressurizes each cylinder at TDC on the compression stroke and measures
how much air volume is required to maintain a specific PSI in the cylinder.
Under 5% leakdown is good. If it is excessive then squirt 2-3 pumps of
engine oil into the cylinder and wind the engine over and reposition at TDC.
If the leakdown rate improves the cause of the pressure loss is rings...if
no improvement then the valve is burnt. If the valve is severely burnt and
ate it's way into the head it could be exacerbated by the increasing preload
as the valve tip moves closer to the rocker fulcrum (not likely).
Best bet is to check the fuel delivery, fuel filter and pressure first, then
try adjusting the valves with the car running using a method of loosening
until the rocker clacks loudly then tighten just until silent then one
quarter of a turn further.
Good luck!
Best Regards,
Tim Ronak
Business Development Manager
Akzo Nobel Coatings
Off: (949) 305-5393
Fx: (425) 955-6268
Cell: (949) 289-3357
email: timothy.ronak@akzonobel.com
VM: (800) 234-6747 ext. 2257#
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