I finally got a chance to start dialing things in and I'm have problems reading plugs. I get no color what so ever on the plug. I think it may be related to the "reformulated fuel" we are stuck with in urban areas. I even went way fat to the point were performance dropped off and still no color. I remember someone talking about looking for the heat line on the ground strap and I was able to do this but remember how to adjust using it.

The heat line on the ground strap is to dial in spark timing. You want that line between the 90 degree bend of the strap and the beginning of the plug threads. If it is on the threads, retard timing and if it is on the 90 degree bend increase timing. Plugs begin to color deep in the plug on the porcelins. There will be what is called a fuel ring that will begin to develop. If you aren't seeing a ring try one step colder plugs. It may be necessary to use an illuminated plug magnifier to see the ring on new plugs. Is your card jetted close to factory settings or is it custom?

The carb is the same size as the stock one, Holley 750. I made changes to intake and exhuast. Primary jet setting seem pretty close at a #73. Im at #82's in the secondaries. 750 double pumper, no secondary power valve. I'm pretty close I would say, its this damn obsessive complulsive disorder that keeps me pullin plugs

Heat line may be related to spark timing, but it can also help you dial in the carb. Changing jets will move the heat line on the ground strap. I've never used the heat line as an indicator for adjusting timing. Timing an engine can be done easy enough with a light and some minimal testing at 32*,34*, and 36* to see which the engine likes best.

From what I have been told, and the method I used, the heat line should be in the same position as wette vette said. Just below the bend and toward the threads. Jetting it richer will move the line closer to the threads.

Do you ever get color on the plugs at any RPMs?? I have a good light tan color at cruise RPM's but my plugs are pretty much white after a WOT run for 1-2 mins and I'm not lean at all. The heat line fluctuates a little, but is always close to the bend.

Griff, I know I'm late getting into this, but I just caught this thread and I'm wondering if there is a typo here or am I just thinking backward. (that happens quite often these days) You said that "richer moves the line closer to the threads" but logic tells me that richer would be cooler so the line would move away from the threads and towards the bend. Please straighten me out here. Thanks. --- Jer

JPclear I believe you are correct. A leaner mixture will be hotter and the added cyl and comb chamber temp will speed up the combustion process which will move the heat line towards the threads. Here is something to ponder. On real hot days the incoming charge is warmer than cooler days thus the combustion is faster. At the same time the air/fuel ratio is fat so it slows the combustion down. The end result timing is probably not going to be affected. What do you think about that crazy idea?

Do a plug check with champion plugs. They give you the best reading even if you dont run them. You cant get any accurate reading on NGK's. You should have a solid ring around the porcelan. If ist broken in any area you have a lean condition. Your line on your strap should be in the bend. If its either direction you are running a too hot or a too cold plug.

It's my understanding that it's not the temp. of the charge that affects things but what temp. does to the charge density. The cooler the air, the denser the air; so more O2 molecules/cyl. charge; so more "BANG"; so more "go fast". I would agree that timing would not be the so much of a concern as the possibility of being under jetted on those cold, crisp days. That's why I like to test and read plugs on those kind of days and suffer with being safely "rich" on the hot, sticky ones. --- Jer