89 LX carb sounds like a detonation above 3k

[Inferno]

When engine is cold everything sounds fine. Here is a scenario. Start engine. Everything is fine. Drive on the highway for about 30 minutes. Exit highway for petrol. Stop on a light. Accelerate on green. When It hits 3k engine sounds like having a detonation. Sound comes from carb intake manifold area.More I accelerate more noisy it becomes. There is no sound if I accelerate slowly keeping RPM below 3k. But when I pass 3k sound starts rightaway.

Thanks

[Demon1024]

check your timing
try higher octane fuel, see if that helps it any

[Inferno]

Tried 94 octane - no difference.
Tried to retard the timing. It fixed the problem for 2 days but then it started again.

[Demon1024]

you may have carbon buildup in the cylinders. try some seafoam, just not in the oil only the intake and gas tank

[2oodoor]

can you record or vidio this sound? if you are sure it is detonation you must be leaning out via the fuel system.

There is slight chance there is water entering the CC as well.