I have 1990 CRX with a DOHC ZC in it. Lately, there has been some valve tap noise. Oddly, it doesn't happen all the time. I though it only happened after trips to redline and back....but somtimes I do redline it and get no noise....any ideas?

I took off the valve cover to see if there was build up of gunk but it looks clean...if that helps.

 

heres a list of things that my honda manual says to check.
1. incorrect grade of fuel
2. ignition timing incorrect
3. fuel injection system in need of adjustment or overhaul
4. improper or damaged spark plugs or wires
5. worn or damaged distributor components
6. faulty emission system
7. vacuum leaks
8. carbon build up in cylinders

 

I had this happen to my car last summer and all I had to do was buy some fuel injector cleaner and switch my fuel grade. I have not heard the noise since then.