Plugs look a little lean... suggestions?

[wcumagic]

Here is a pic of a plug from the car after running about 10 miles.  She looks a lean to me and a friend of mine.  What do you think?  He suggested I throw 'em back in and drive another 10 or 20 miles and check em again, so I will do that tomorrow, but he also suggested if its TOO lean, it'll kill the engine. 

I've got a 17056259 with the factory metering rods in it.  I've done the modifications in recipe #3 in Cliffs book.  The engine is a 340 with a moderate cam in it (I dont know exactly) and head modifications and headers. 

What size metering rods you think I should throw at it?  Also, do you think the plugs I've got in it are the right heat index?

[Cliff Ruggles]

It's impossible to read plugs and determine rich or lean.  If the engine is getting too lean A/F it will let you know.

This will include stumbling, hesitation, surging, lack of power, and taking a LOT of throttle angle to get the vehicle to move.

Your carb has an APT system, have you tried adjusting it using our "tip-in" procedure?...Cliff

[wcumagic]

Cant read plugs?  "I" probably cant do it well, but there's been people doing that for years and years, including NASCAR before fuel injection (Including my friend since the early 60's).  I've seem 'em at the dragstrip doing it, too.  What do you mean, maybe I'm confused?  I just wanted to get your opinion since you're the guru on carbs.  Do you suggest getting an O2 sensor and gauge to tell?  how else?   

When I spoke to you on the phone, you said I probably wouldnt need to adjust the APT, so I didnt think another thing about it. 

I'll try that first though, thank you. 

[Cliff Ruggles]

It is IMPOSSIBLE to read plugs to indicate part throttle A/F ratio to your engine.

This new fuel makes it even worse.

The only way folks used to read plugs with any sort of accuracy, was to make a full throttle pass, then shut the engine down immediately after crossing the finish line, coast to a stop, then pull a plug and look at it.

Even doing that was a poor indicator of what's really going on....IMHO.  I say that, because any idling at all will blacken them right up on most "high performance" engines, as they use big cams with lots of overlap, so tons of unburnt fuel finds it's way thru the engine at idle and low rpm's.

Tune at the track by ET and MPH, not by reading plugs.

Tune on the street by setting the idle mixture screws for best idle quality at the leanest settings, best fuel economy, etc.

Tune the part throttle by driving the vehicle, and evaluating throttle response, smooth off idle, smooth/clean power for "normal" driving situations, and good power without any surging, flat spots, or too much throttle angle to acheive vehicle speed(s).

Tune the full throttle by best power production, either by engine dyno, chassis dyno, or drag strip ET/MPH.

"Seat of the pants" testing will get you close, but ultra fine tuning needs some sort of measuring device(s) to know when it is perfect.

I would also mention here that Q-jets are very efficient at light throttle openings.  If you saw the plugs from my engine, they are clean, and light tan to almost white.  The carb and distributor are in perfect tune, and the engine performs flawlessly in all areas.....Cliff