Any Ideas on Lean Plug
Thread Starter
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
Any Ideas on Lean Plug
My new 496 rebuild has a couple of hours on it now. I pulled the plugs to look and the #3 plug was pure white with a little yellowish deposit on the ground bar. The other plugs are tan or light brown with some black carbon around the base of the threads (I assume this is because I ran it rich during cam break-in). The #3 plug doesn't have this either.
Tonight I will run some tests to find out what is going on. I was hoping I could get some suggestions on what to look for from the experts.
I am pretty sure I do not have a vacuum leak from my accessories (quite a bit of testing here). The engine does not have an appearant miss, although I am not an expert and it is possible that I am not noticing it. The engine pulls very strong once above 2500. Idle is rough, but I assume that is the cam. I am pulling 8" of vac at idle (255/263 @ .050 cam) and don't get any fluctuation on the needle. The plug wire is good, but I haven't yet put a light on it to verify that it is firing. The distributor is brand new now, although the first hour of running was on the original distributor.
Thanks for any suggestions you may have.
Tonight I will run some tests to find out what is going on. I was hoping I could get some suggestions on what to look for from the experts.
I am pretty sure I do not have a vacuum leak from my accessories (quite a bit of testing here). The engine does not have an appearant miss, although I am not an expert and it is possible that I am not noticing it. The engine pulls very strong once above 2500. Idle is rough, but I assume that is the cam. I am pulling 8" of vac at idle (255/263 @ .050 cam) and don't get any fluctuation on the needle. The plug wire is good, but I haven't yet put a light on it to verify that it is firing. The distributor is brand new now, although the first hour of running was on the original distributor.
Thanks for any suggestions you may have.
Thread Starter
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
I checked again tonight and there is some carbon build up around the base of the threads like the others, so there is/was some combustion in there. I can't understand why it is running lean.
Melting Slicks
Joined: Dec 2006
Posts: 2,669
Likes: 3
From: Kingston Ontario
To check if #3 is firing remove wire while engine is operating and note performance change. You can try with a different plug wire to see the expected result.
I would remove plugs, clean and re-install them and see if the problem still exists. It is possible that you had deposits on the #3 plug prior to engine start-up, and that has given you the current plug condition. If the plug is glazed, it could also cause a misfire on #3.
Clean, install, run engine and re-inspect the plugs.
I would remove plugs, clean and re-install them and see if the problem still exists. It is possible that you had deposits on the #3 plug prior to engine start-up, and that has given you the current plug condition. If the plug is glazed, it could also cause a misfire on #3.
Clean, install, run engine and re-inspect the plugs.
