running lean?

[Flanders 46]

I'm a bit stumped --

My plugs are white. My exhaust values are white. I'm not running any high ethanol gas, so I tend to think I'm lean.

 

I've got a Holley Street Avenger 570, which should be good for my 351W 4v up to 5000-ish rpm. Jet size is 54 at sea-level (where I'm at), although I took a big jump up to 60 (and 65!) to alleviate the problem with no luck. After a long hwy drive (hours) the plugs are white!

 

No vac leaks, as far as I can tell. Could it be a fueling issue? The car idles great, and there is no pinging. The engine drove very nicely, so I wasn't expecting white plugs (actually, if anything I should be running pretty rich with 65's in there).

 

I've got splitter feeding the carb, and there was an inline fuel filter (unecessary, I know) before this. Maybe the filter was causing a pressure drop? Although this would surprise me.

 

Any way to test the fuel pump itself, or are there any other suggestions?

[LoneWolf2U 136]

If your still that lean I would try going up on the jets.

I put 66 in the 68 when I dropped it off in Washington to run correctly and its a 289.

[Flanders 46]

wow. Holley even says to only go up a jet size or two (they recommended 56). I figure 65 is quite a huge jump already. From factory (sea-level) it's 54 primaries and 65 secondary.

[LoneWolf2U 136]

Try 60-62 in pri side and recheck plugs.

[Flanders 46]

I was running 60's at 780ft (according to Holley sizing, I should have only needed to go up a couple sizes at 780) and was still white white white. That's when I jumped to 65's. Over the next 20 hrs I drove down to sea level...and still white white white.

[1969 Mach1 14]

What type of ignition are you running? If it is a CD type like MSD, Crane, Mallery, etc. the plugs will stay real clean with very little color to them.

 

I don't prefer the Avenger series (thats just me) but if you like the Avenger's, the 670 cfm would be better suited for the 351w even if your calcs say 570 cfm is large enough. The straight leg boosters and vacuum secondaries in the Avenger's are very forgiving if the carb is slightly oversized and the car should still run fine. On mild performance 351w's most people run 650 cfm or 700 cfm if a double pumper or 750 cfm if a vacuum secondary.

 

The Holley carb book I have states if the carb is correct for the application the jetting should only have to be changed one or two sizes. Along the lines of what Flanders also mentioned.

[sportsroof69 13]

What are you calling white? If the ceramic in the middle is bone white, then you are rich. Look at the ring on the plug for color, and the ceramic should start turning a chocolate color as you lean the engine, and that's what you want.

[1969 Mach1 14]

What are you calling white? If the ceramic in the middle is bone white, then you are rich. Look at the ring on the plug for color, and the ceramic should start turning a chocolate color as you lean the engine, and that's what you want.

 

Is that correct? I have never heard of it in that manner.

[Flanders 46]

yeah, those colors seem backwards to me :-)

I was originally running a pertronix billet flamethrower dist (ignitor2) but drove the last 15 hrs with stock dizzy. (pertronix failed due to not being properly powered)

[jkskinsfan 19]

I seem to remember reading somewhere that having the timing advanced to far could cause plugs to be white. Also plugs with the wrong heat Range (Too Hot) could also do this. Colder plugs might help.

[sportsroof69 13]

Do what you want, but if the porcelain is a bone white color, it's rich. What does the ring look like? Can you post a good pic?

[sportsroof69 13]

Here you go. A quick search, and it says the exact same thing. Read under the third picture.

 

http://www.angelfire.com/fl4/pontiacdude428/Readplugs.html

[CandyAppleRed 10]

It also says "This is valid for track only (not street driving)".

[sportsroof69 13]

It says that because the only real way to check a plug is to run it at WOT and kill it. This is true for any engine, because any idle time makes plug reading flawed. They're not going to tell you to go try it on the street.

 

It still doesn't change the fact that bone white porcelain = rich. Use some common sense with it. He had a plug that he said was white. Well, what was white? Is he talking about the porcelain? If so, he added 11 jet sizes, and it's still white? That's because white porcelain means it's rich.

 

Like I said, do what you want. Call what I'm saying backwards. I don't care, but I'm can promise that it's over jetted.

Edited October 29, 2011 by sportsroof69

[Flanders 46]

sounds logical -- http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm

 

this is the chart I grew up with, so excuse me if I'm puzzled!

[1969 Mach1 14]

Here you go. A quick search, and it says the exact same thing. Read under the third picture.

 

http://www.angelfire.com/fl4/pontiacdude428/Readplugs.html

 

I skimmed through the above article and with one important difference it seems correct. Like CandyAppleRed stated "This is valid for track only (not street driving)". With that I think the difference being the plugs being read for track conditions only have 10-15 minutes, maybe a little more, run time on them. Which is not enough use for coloration to build up anywhere else on the plug, if it is going to. That is why I don't think it would apply directly to spark plugs with 10k or more miles on them.

Edited October 30, 2011 by 1969 Mach1

[CandyAppleRed 10]

I guess it is difficult to teach an old dog new tricks. I have to believe "valid for track only" means what it says. On a street driven vehicle taking a plug reading only after WOT seems invalid. I would be looking for plug condition after the engines intended use. If your engine only sees WOT on rare occasions why use that to judge plug reading. You would want to see the plugs condition after it's normal use. At least that's what I would think....

[sportsroof69 13]

Does your engine know if it's on the track or the street? Rich is rich, and it's something you can't change, and a rich condition will do the same thing to the plug. The engine doesn't care what you're doing to it. That page was The first thing that came up when I googled it, and it said the exact same thing that I said, before I googled it. Bone white ceramic typically means rich. The rest of the story will lie in the ring and ground strap. The question I asked in the post still hasn't been answered. What does the ring look like?

 

Cars going down the track are looking for the same thing cars on the street are looking for. An optimum A/F ratio. The best A/F ratio gives you best performance, drivability, and fuel economy, while keeping the plugs clean, and making the engine happier. It doesn't matter if it's in the track, or the street. We are all looking for the same thing.

 

 

 

With that being said, you can not get a good plug reading if the engine was idling when you killed it, and pulled the plug. The plug changes instantly when you let it idle, and if it's tuned right, a plug at idle will show rich, because a rich idle circuit will give you a faster rev, until the main jets take over.

 

 

Again, he added 11 jets and it still showed a white ceramic, and you guys don't think it shows rich? You can look at it two ways. It shows rich, because the engine idled, and that's ok. Or the ceramic was white, he added 11 jet sizes, it's still white. That's not an indication to step back and think that maybe white ceramic means it's rich? So you guys think he should just keep jetting it up?

Edited October 30, 2011 by sportsroof69

[CandyAppleRed 10]

I would not offer advice to him on carb adjustments. I make no claim as to my expertise. I only posted because like others, this is contrary to what I believed for a long time. And the opposite condition would make even less sense to me. If rich is white, would a lean condition leave the ceramic black and fouled? To me anyway, that just sounds like there has been a rift in the time/space continuum.

[sportsroof69 13]

No, black is rich past the point of the bone white condition. You can't base plug reading off of just the ceramic. It's a whole combination of things. The ceramic should be a light chocolate, or tan color, and there should be about a full turn of color change on the ring. If the ring is black, and sooty, it's rich, and that it normally accompanied by bone white ceramic. You have to look all the way down the threads of the plug. There is a lot more to knowing what your engine is doing than just the color of the ceramic.

[MikeStang 247]

Kens speed and machine is spot on, every time I have taken advice from him it's been deadly accurate. I have a pontiac also if your wondering why I use Ken lol.

And the above stated is correct about the light brown to chocolate color on e porcelain.

I can bring a plug from my motor that we dynode, and get a pic and you will see what a damn near perfect mix looks like, my afr was ideal when we ran it....funny thing is the carb is an hp 950. That I pulled off my Pontiac 455 and bolted on to the 408 with NO changes in jetting etc....and e Pontiac was slightly rich but I left it alone cuz of the nitrous lol, but the 408 had more aggressive heads and cam profile, so it worked out......the statement about track only is in my opinion put there so people know the way to maximize hp, but it holds true for street ad well.

Mike

[MikeStang 247]

Oh the carb calculators are goodnto a point, they use standard measurements with out taking into account any modifications....they are IMHO designed for stock motors.....really look at it....if you run the standard 525 or what ever it calls for on your motor then swap to say a 650dp you will feel a seat of the pants difference, and if you can actually feel it then it did some good.....my dyno guy said you can keep going bigger and make more power ...but to a point where your just wasting fuel and the hp to dollar value negates your gains.

I could have put his 1050 carb on my motor and made more power but at the sacrifice of fuel I would be wasting.

If your motor is stock the 525 or what ever you have is fine....I ran a 650 on my stock 302 and it woke it up...so it's a toss up ...better fuel milage or more power

[1969 Mach1 14]

Oh the carb calculators are goodnto a point, they use standard measurements with out taking into account any modifications....they are IMHO designed for stock motors.....really look at it....if you run the standard 525 or what ever it calls for on your motor then swap to say a 650dp you will feel a seat of the pants difference, and if you can actually feel it then it did some good.....my dyno guy said you can keep going bigger and make more power ...but to a point where your just wasting fuel and the hp to dollar value negates your gains.

I could have put his 1050 carb on my motor and made more power but at the sacrifice of fuel I would be wasting.

If your motor is stock the 525 or what ever you have is fine....I ran a 650 on my stock 302 and it woke it up...so it's a toss up ...better fuel milage or more power

 

For the most part I agree with MikeStang. However, for good drivability there is a limit to carb size on a street driver. If you cross the thresh hold of too large of carb stumbling and surging during accelerations will occur that cannot be eliminated by tuning. As the carb size increases on a given motor, for example a 351 C.I.D. motor, the air speed through the larger venturies decreases at any given RPM. This then requires higher engine RPM's to obtain the air speed required to start up the carb main circuits. The accelerator pump provides fuel during acceleration to overcome this delay to prevent surges and stumbles. However, if the carb is too large this delay takes too long (clock time) and the accelerator pump cannot be tuned to supply enough fuel to "cover up" this delay. Thus, stumbling and surges during acceleration occur.

Edited October 31, 2011 by 1969 Mach1

[Lemon Owner 11]

For the most part I agree with MikeStang. However, for good drivability there is a limit to carb size on a street driver. If you cross the thresh hold of too large of carb stumbling and surging during accelerations will occur that cannot be eliminated by tuning. As the carb size increases on a given motor, for example a 351 C.I.D. motor, the air speed through the larger venturies decreases at any given RPM. This then requires higher engine RPM's to obtain the air speed required to start up the carb main circuits. The accelerator pump provides fuel during acceleration to overcome this delay to prevent surges and stumbles. However, if the carb is too large this delay takes too long (clock time) and the accelerator pump cannot be tuned to supply enough fuel to "cover up" this delay. Thus, stumbling and surges during acceleration occur.

 

It takes a pretty big carb to do that. I put a 650DP on a 250 pre crossflow inline six with a 2V head and it loved it!

[1969 Mach1 14]

It takes a pretty big carb to do that. I put a 650DP on a 250 pre crossflow inline six with a 2V head and it loved it!

 

 

I can't argue your statement of your 650 DP on a 250 inline 6 because I had a 650 DP on a 351w and it was always too lean and runs much better with a 700 DP. But I will say the same motor ran worse, lazy and more sluggish, with a 750DP. Also, keep in mind on your 250 6-cyl. situation that a 650 DP has both fairly small diameter primary venturies and straight leg boosters which are second to annular boosters as far as sensativity to air flow. Thus, the main circuit starts with less air speed through the booster venturi than say a down leg booster which will reduce the chance of stumbles and surges on acceleration.

 

However there are times when even a slightly oversized carb causes problems. Put a slightly oversized carb on a motor with a single plane intake and a fair sized camshaft and you will get stumbles and surges on acceleration that you cannot tune to get rid of. This seems less noticeable on automatic transmission cars. Especially if the torque converter has a higher than stock stall speed.

Edited November 1, 2011 by 1969 Mach1