Reply With QuoteUh, I believe you have one GOOD hole. They should be a light tan. Black and sooty means too rich. But then again to read a plug you can't let the engine idle more than a few seconds or you'll get a bad reading. I hope that made sense?!?
I have a mild 500 BBC w/871. Plug on # 7 is light tan, all others are BLACK and sooty.
Good I have a bad lobe or other intake valve problem? Haven't run compression test and I'm wondering if I wiped a lobe would that leave me a little lean in that hole?
Uh, I believe you have one GOOD hole. They should be a light tan. Black and sooty means too rich. But then again to read a plug you can't let the engine idle more than a few seconds or you'll get a bad reading. I hope that made sense?!?
460 is right,the plugs should all be light tan on the white ceramic area of the plug. Do not worry about what the threaded area looks like.
Do your primarys first,then the secondaries.
BradP, how do you check your plugs? The way we did it & they still do in CUP cars is on the final lap of qualifying after they cross the finish line it goes in neutral at about 8000 RPM and the ignition killed simultaneously to maintain the correct A/F mixture on the plug at max speed/load. If you even idle for a few seconds it dilutes the true color of your plug and thus the wrong reading.
For you the only real way is WOT at your maximum RPM & kill the ignition & then pull the plugs and make sure you started with new ones! Wherever you are at and put some other plugs back in so you can do a real good evaluation on land with the ones you just took out with good light & under a magnifying glass so you can look deep inside.
This reading was done in driveway after idleing to launch ramp, not a long idle but I know I should read them after WOT. My qustion really is with one hole reading so different should I start looking for a problem before stepping the jetting back down. I holed a piston last year from leaning out and I'm trying to avoid a repeat.
[This message has been edited by BradP (edited May 30, 2002).]
A couple things come to mind.One is maybe an intake gasket that got sucked in at the intake port of the tan plug or maybe its just clean from a water intake leak.If all plugs are black but one you definately need to look for the problem.Im betting on one of the two scenarios.But I could be wrong.
Thanks Jrocket.
You kind of lost me on the intake gasket sucked into the intake port. How would this cause a lean problem, air/fuel mixed pumped into valley? If it's a water problem would it show a little rust on the plug?
I know the next answer, leak down test!
If the intake gasket is not sealing correctly around the port it will suck in raw air.Making the air fuel mixture very lean in that one cylinder.If the one cylinder is getting water in it,most of the time the plug will be gas or water washed looking.Its not right to have 7 of one and one of another.They should all be close..
A lot depends on the intake manifold you run. Wiends and Cragers (flat floor type) generally run the #7 and #8 hot. Peak floor manifolds such as BDS or Mooneyham tend to run #7 and #8 rich. Also consider that Blowers screw the fuel around in many directions, mostly to the front of the engine. If you are concerned about #7 cylinder, do a leak down test on it and compare with the other cylinders. Far more accurate than compression check. If you really want to Jet the motor correctly, here's how I do it. Use a NGK plug (due to it's cad plating). Use a #7 or #8 heat range, 8 being the colder plug. Make a full run and cut the engine off while closing the throttle. Remove the plugs. Wipe any black soot off of them with a rag. Look at the cad plating on the end of the spark plug. If the cad is burning off the plug..you are close. If all the cad is still on the plug..you are fat..lean it. This is the conservative way and will get you close. If you want a serious tune up, do it this way. Not for the faint of heart. Install #7 heat range plug. Make a run. Look at the cad plate..and now the very end of the ground strap. Bump the blower or lean the fuel mixture until you see the end of the ground strap just start to melt off (the cad will be long gone!). Fatten the motor 2 jet sizes (1 if you are brave) and install #8 or #9 plugs in it.
Hey Fiat48, who do you work for? I used to live & work there in the 80's. Ever heard of Adams Custom Engines or Intreped?
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