ignition experts come on in.

[yetterben]

Here is the story. In my quest for power on my 73 i am always fiddling. Always get more power when i fiddle

I have a zx motor and dizzy 3 screw su's flamethrower coil. timing set to 14btdc.

Here is the question. My plugs where set at .38 or so car was pulling hard. Running a little richer plugs dark dark chocolate. So me being me and cant leave enough alone i opened the plugs up more to .44 or so Power increased exhaust stench did too . Blows mild black when i crack here open at 7 grand. Power is better alot better. But now my plugs are sooty again. Is this a bad thing or did i now effectively make the plug colder buy opening the gap? Should i lean her out a little now with a larger gap?

I guess i am curious as to how plug gap directly affects combustion.

[doradox]

Here is the story. In my quest for power on my 73 i am always fiddling. Always get more power when i fiddle

I guess i am curious as to how plug gap directly affects combustion.

http://lmgtfy.com/?q=plug+gap+and+combustion

[yetterben]

Okay put everything back to stock. b6es-11 plugs. 10btdc su's 2 3/4 turns out. at idle the plugs will turn a nice dark mocha color a little o the rich side. I took her down the back roads for some wot passes threw 1st and 2nd. Shut it off foot still on the gas coasted to side of road. Pulled all plugs. There white. The outter ring is black though. I have always been told the outter ridge near threads is where to look for jetting after wot.

Help me out guys. How can it be dead on at idle and go to bone white and wot. On the other hand it pulls like a mother and i would think if it was lean it would throw a fit.

[yetterben]

http://www.empirenet.com/pkelley2/sparkplugreading.html

[JimmyZ]

Disassemble and clean your carbs. Get a synchronizing tool and sync them. Pop open any manual for early Z's (haynes fsm clymer etc) and set the mixture properly. I got a colortune (google it) and think its great for setting idle mixture.

Do a search on leaking throttle shafts for SU's. Its also possible that your carbs are worn out or have damaged parts. You'll find that fuel level in the float bowl also affects mixture.

If you REALLY want to get anal about achieving the best mixture look into something like an LM-2 http://www.innovatemotorsports.com/products/lm2.php

The LM2 is AWESOME!!! I'm currently using one to tune an LS-2 crate engine. It has great reviews and many tuners stand by it.

Jim

[geezer]

I would give the plugs another read after a period of normal driving conditions at varied speeds. Here's more plug reading info. Outdated method perhaps, but still tells the story.

[yetterben]

Carbs are brand new. I have a factory service manual i kn ow how to set the carbs. Sorry if that seems snooty. not a noob with cars. Just confused how i can attain perfect mixture between 500-3000rpms.

I also have a uni-syn.

Edited July 30, 2009 by yetterben

[yetterben]

I have come to the conclusion at wot the plug is to hot to leave soot on the porcelain. So my engine is a little rich at idle but better than to lean.

[ozconnection]

I have come to the conclusion at wot the plug is to hot to leave soot on the porcelain. So my engine is a little rich at idle but better than to lean.

JimmyZ has the right idea. The ability to monitor and data log your air/fuel ratios is by far the best method of 'tuning'. These options are available for all of us so even if our cars/engines are old tech, there is no reason why we can't tune with modern, high tech tuning aids. After all isn't that what we want, the ability to tune our engines to a level of performance that was unobtainable even a decade ago?

I can appreciate the fact that some guys years ago had the knack of tuning their engines to extreme levels. They certainly trashed quite a few motors along the way to achieve their goals. If you have lots of spare cash to follow in the footsteps of our heros, then go ahead.

The point I'm trying to make is, can you tell when the idle is 'a little rich?' I mean, is it 12.2 or 11.6:1? What are your cruise mixtures and most importantly, what are your WOT mixtures?? All of this information can be logged so you can later sit down with a coffee and ciggy and ponder your next modification. Then, after the mod, do another logging session and see what effect your change (singular!) had on your engine's tune.

I tune my engine this way now. I have a few small bugs to iron out but the speed at which you can isolate what works and what doesn't is fantastic. The 'seat of your pants' tuning will only get you so far, but this new 'high tech' approach is awesome!

Cheers and good luck.

[yetterben]

No Doubt a wideband would be good. Its on the list. It was just confusing how it could be so dead on at idle but look weird at wot. Then it hit me at wot or even cruise the plug is so hot it cant leave a mark on the porcelain. I have looked all over the net and this is what people say. MY base ring is nice and brown so jetting is good.

The way su's work i thought was linear and that if idle was right then the rest of the band would be right to. Barring any major engine changes that is.

i did create this monster as well.

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and after the turbo i tried a camden.

It has jsut been a long time since i have messed with a boinger aka piston. You being from oz should understand

So i am buy all means not a noob. But judging but previous wideband experience i could look at my plugs at idle and say i am in the 10's rich i know but i feel safer there. I think so much myth is tossed around about plug reading.

Here is the car in question.

Edited July 30, 2009 by yetterben

[JimmyZ]

Nice Z! Mine was originally that color. I miss it. Unfortunately the wife wanted red and I thought it was worth a try.

.

The way su's work i thought was linear and that if idle was right then the rest of the band would be right to. Barring any major engine changes that is.

Not necessarily linear. Your needle can determine your fuel curve. It's possible to have the mixture right at a point in operation such as idle but be way off at a different manifold pressure. Most of us with stock engines assume that once we set things up as the manual says that all is well. (not always so) SU's are really neat to me because of their simplicity but it would be nice to have a more modern way of tuning them. True, an O2 sensor on each bank would be a good start but having the ability to isolate each side of the intake system and data log manifold pressure on each bank would be nice as well. By doing this you might catch a snagging carb piston or other anomally. One could probably spend a week tweaking things to perfection.... But what a fun week!

Jim

BTW.. Cool NGK clip Geezer! (Sp plugs)

Edited August 4, 2009 by JimmyZ

[gira]

Fellow SU users,

We've spent countless hours trying to get an air fuel curve similar to an FI car out of our SU using Z cars. The fact is it's next to impossible. The function of the demand (manifold pressure), SU piston oil which can affect the location of the piston vs time, any modifications such as an L28 bottom end or headers, the needle grind and jet nozzle size. I mean that's a lot of old fashioned metering to think you can dial in perfectly. It just ain't gonna happen. If you have an upgraded ignition system that throws a decent spark, then you don't have to worry much about fouling or running rich when idling. Rich is good for start up anyway. As long as it pulls like it's supposed to and isn't fouling plugs or blowing a lot of black smoke, i'd go with it.

See you,

Greg Ira