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Discussion Starter #1
Hi all. I'm entering the dark art of reading spark plugs and would value any advice from masters of this dark art.
A bit of info, I'm using NGK BP6ES Plugs and the original Solex carbs. Since the engine rebuild I have been tweaking said carbs until I'm happy with the way she starts and runs. Starting is easy first time....usually with no choke and just a small amount of throttle. After about 30 seconds she'll idle on a cold engine at around 500rpm although a tad lumpy. When engine is up to temperature and after a good run, she idles around 8-900rpm. Throttle is responsive engine pulls well and pulling away from standstill is relatively smooth...and fast if need be. So all seems good. Only I'm not too sure, I'm told these engines run quite rich, but if I increase the mixture any more than it is now she pulls away really sluggish and stinks of fuel but looking at my plugs I'm thinking it's running a tad lean. Have taken out three of the plugs, all 6 are the same , would like to have your input and wondering if changing to NGK BP7ES would be better? Over to the guru's 馃檪
 

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Push hard and live
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From what I can see, the plugs look more or less ok.

I鈥檓 assuming you have a 2600, or a very rare twin plug head for a 2000.

Which three did you pull? Alternating cylinders, or three in a row?

A recognized issue with the Solex carbs is shaft and body wear, leading to gradually leaning the mixture. Your plugs don鈥檛 appear unusually lean.

On these engines and carbs, if it starts, idles, accelerates, and runs ok, you鈥檙e in the sweet spot. Leave it alone.
 

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Discussion Starter #4
Thanks for your reply, yes it's a 2600. Plugs were from cyl 1,3 and 5. I have one plug running slightly richer than the others, nothing I can do about that! As you say there will be wear in the carbs. Will try the NGK 7's as I'm about to do a full service and see if there's any difference.
Cheers,
Brian.
 

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Thanks for your reply, yes it's a 2600. Plugs were from cyl 1,3 and 5. I have one plug running slightly richer than the others, nothing I can do about that! As you say there will be wear in the carbs. Will try the NGK 7's as I'm about to do a full service and see if there's any difference.
Cheers,
Brian.
IMHO slightly lean , what fuel are you using? (my old sage mechanic would say) " better a little rich"..:grin2:
 

Push hard and live
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One plug can be a little rich and the other two slightly leaner if there is a small synchronization imbalance.

For a plug reading to be most accurate, you need to be rolling down a road at highway speed, reach over and put it in neutral and cut the ignition, and roll to a stop. Then check the plugs by the side of the road. Otherwise, you鈥檙e checking the mixture of the idle circuit.
 

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I've done fully instrumented dyno testing on hemi headed engines. We typically had O2 sensors in each exhaust runner as well as one at each collector. Be aware that it was not unusual for the individual cylinder to be +- a point or more than the collector. Which makes sense.

You have to give an engine what it wants. People tend to chase lambda #s, or in your case gas stoich #s (careful, is there ethanol in that fuel? It changes stoich).

If you have set up the car to 14.2 (idle? WOT? lightly loaded cruise?) and it runs well for you, who am I to say that's wrong, but my experience would suggest that is lean in any situation requiring power.

YMMV


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I like the thoughtful replies here and agree with them. The specific pinkish coloration is modern "fuel" and depending on the run before pulling the plugs, they look Ok. I look at coloration only on the high-speed circuit, and color here will reflect heat range and mix. High speed circuit engine operation for 10-15 minutes, with quick shut down and plug read. WHITE center insulator is too lean, bubbly and greenish, detonation territory, or wrong heat range. I like a more uniform pinkish coloration on the whole center insulator. The dark areas (blackish) are soot from incomplete combustion, not unusual for idle circuits. I would leave well enough alone, unless you have good reason to fiddle with it.
Just my opinion from my own observations over time.
 

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I've done fully instrumented dyno testing on hemi headed engines. We typically had O2 sensors in each exhaust runner as well as one at each collector. Be aware that it was not unusual for the individual cylinder to be +- a point or more than the collector. Which makes sense.

You have to give an engine what it wants. People tend to chase lambda #s, or in your case gas stoich #s (careful, is there ethanol in that fuel? It changes stoich).

If you have set up the car to 14.2 (idle? WOT? lightly loaded cruise?) and it runs well for you, who am I to say that's wrong, but my experience would suggest that is lean in any situation requiring power.

YMMV


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I am able to get Alcohol free gas (unleaded) (94 Oct) I mix 6 oz. of Marvel mystery to 10 gallons, it is not a daily driver (maybe 400 Miles a month in the summer). On the hottest days (95+) and a brisk run, the the water temp is perfect. I am using Pulstar plugs- BE1H 10.
 

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AFRs

If you are going to install a meter for measuring your AFRs I strongly suggest a Wide band meter. You cam monitor your AFRs and with some units like Zeitronix, you can download runs to see afr at all rpm & loads.) while driving.
AFRs are quite different for different engine loads. Fuel economy and power is critical at different levels. A well tuned carb setup should read in the ranges below:

Idle 14.6 to 16.0
Tip in: 11.5 to 12.5
moderate throttle opening acceleration 12.5 to 13.2
wide open throttle 12.7 to 13.5
steady state cruising 14.0 to 14.2

If they are lower than these you are wasting fuel and not making the power you should.
Higher and you are too lean.
 

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@Alfar7
Seems to me the Factory Carb setups pre emission, tend to run toward the lean side with U.S. ethanol fuel mix. On several occasions we have adjusted air correctors and jetting to get the correct ARF, over the years on the earlier euro carbed 2 litre and 1600's. The jetting on my 64 1600 is as from the factory and the AFR is spot on with the ethanol free fuel UNLEADED. With all the $ we spend keeping these things going it is certainly worth the $250 or so to do a good job dialing in .... or get to someone who can....
 

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Reading spark plugs.

Just my 2 cents because I was playing Mr Dyno yesterday.
If you want to read a plug you need to do a wide open throttle (WOT) run in 3rd or 4th and cut the ignition (without locking the steering). I used to do this when I was younger and lived in a area where there where no people.

Last week I installed some mild cams in a stock NORD engine in my alfetta.
Stock engine stock alfa DHLA carbs.
I fitted my air fuel ratio (afr) meter and yesterday did a few laps around a race track.
I had already put larger idle jets in the car because they where lean. So standard 55 idle jet was replaced to a 60. Still lean but on the 40 DHLA alfa carbs you cant tune the idle air corrector easily so..........(that's another story).

145 main 772.8 emulsion tube and 210 air corrector 32mm chokes. Standard alfa 40mm DHLA jets for 10548 cams here in Australia.
I went from a standard 145 main to a 150 main. Mixtures where good but leaned out in the top end over 6000 rpm.
Fitted a 190 air corrector and went way rich 10.1 over 4000-6500 rpm (very surprising to me).
Fitted the original 145 main with the 190 air corrector and hit 12.0 from 4500-6500.
Every engine is different and in my case I was surprised by the difference the air corrector made.
Stuff EFI I love carbs.
 

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Plugs /2600 and Dellortos

Oh good reading the post above i have some possible settings for my 2600 which runs triple DHLA 40s. On the basis that the cylinder displacement is about the same on 4 cylinders on a 1750 as 6 cylinders on a 2600 the settings could be similar.

Trying to stay on thread topic

Plug check 1. After 45 laps of Goodwood and a fast drive home

6,5,3 Brown
4,2,1 Black

Plug check 2 . New plugs . After a 250 miles round trip to NAD running most at steady 80 mph.

6,4,2 Black
5,3,1 Brown

So what does that prove then ? Not a lot I guess.

Current Dellorto jetting is

Chokes 35
Main 145
Emulsion 7772.5
Air Corrector 210
Idle jet 55


alfettaparts figures

Chokes 32
Main 145
Emulsion 7772.8
Air Corrector 190
Idle jet ?

NB other than a 200 Air corrector this is std settings for an Alfetta with DHLA40F emission carb - as excel sheet attached. I have performance carbs so this is why I guess thats why there is a difference

So no comparison there - but I don't have a dyno.

The only thing I do know is the 2600 runs out of puff above 5000 rpm with a Choke less then 35mm. With 35mm I ran to 8,000 on the track a couple of times as the power kept coming

Full list of various jetting attempts attached, for light reading - yes , I know I should go to a professional but is fun experimenting.
 

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