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Message: [QUOTE="Micahdawg, post: 884633, member: 21668"] My KX just started to develop a very slight knocking noise at low rpm. I'm wondering if it could be from the spark plug....maybe I need hotter or colder? The bike is a 1989 KX250, standard bore, I split the case and put new crank bearings/seals in. I reused the crank/rod assembly which felt pretty tight. I also installed a used piston/wrist pin with new rings (piston was in good shape and felt tight too). I ride at 500ft over sea level and jetted the carb to FMF spec (52 pilot, 174 main). Before this ride I had the head off and rebuilt the KIPS with two new subport valves. The bike was hard to start when I got it out in the morning, but ran for about 2 hours all day perfectly fine. No boggin, no hard starting, no loading up. Pulled great down low and on top just as it has since the rebuild. Compression is at 155. The bike doesn't seem to make a noise at idle (idles kinda high), but when rolling in 1st with load on the bike and giving it about 1/4 throttle it makes a weird little knocking noise that goes away as throttle increases. Could a spark plug make this kind of noise? It's not very loud like a mechanical BANGING noise....and I can't imagine it's the rod bearing as it would probably not go away with rpms. Oh, I use Klotz at 32:1 and 92 octane also. Any help or suggested plug would be nice. I think I've got a B8ES or BR8ES in there now. Micah [/QUOTE]