On my 289 cyl. number 6 always had shown a hotter/lean spark plug condition. It's close to white while all the other are pale brownish. Particuliar to that same spark pliug is the threads are oily. I ran a compression test and all cyl. were steady at around 130-135. Its a performer intake and I plugged the vacuum gauge onto one of the vacuum port wich was common to the runner feeding cyli. 6 and at 2000 rpm the needle stayed steady at around 25 inches. What else than a leak could cause that situation?
I put 3000 miles on that recent rebuild and that's been like this since day one...the engine runs good,no oil consumation,easy starting,good idle altough lumpy because of the cam.
What else should I check?
I would suspect that you have a small vacuum leak on the bottom side of your intake manifold runner that corresponds to the lean cylinder. Since the leak would be pulling in air and oil mist from the cam valley that would also explain why there was also oil on the #6 plug that weren't on the others.
Thanks mach1....Would retorquing the intake bolts be the way to cure that leak? It's a performer and that reminds me the aluminium parts need to be retorqued once in a while don't they? does 30-35 pounds sound like right as a good torquing ?
Just a note concerning my initial message is the oil deposit is only on the threads of the spark..the tip and insulator are close to white with no oil.
I've checked for leaks without success and torqing to 25 was all good....now has anyone ever heard about faulty intakes that by configuration could be responsible for a bad fuel/air mixture and thereby be the source? It's been suggested to me by a person who had as much as three temperature range showing on the sparks: too rich,just right and lean.....that was on one of the high-rise "cobra" repro.Anyone ever experienced similar problem?
This is an area where Smokey Yunick though there was much to learn. His belief was if you could equalize cylinder temps by varying timing, comp ratio, cooling, for each hole, you would increase the point at which detonation would occur. He said the #5 cyl on SBF would get the hottest due to inefficient water cooling. Interesting.