Rough Idle-Colortune-weak spark?

[Jonnyc]

I just purchased a colortune kit to try to find what is going on with my rough idle.

My idle fools me a lot - but I'm learning some of it's tricks! When it's cold the idle is not bad (not perfect either, but not bad). After warm up for say 20 minutes it gets very rough! Mostly in traffic, stop lights etc. If I disconnect the vacuum hose to the distributor - the engine runs much better - which leads me to believe I'm running rich for some reason?

I installed the Colortune plug and watched the sparks! But it doesn't look right - then again this my first time. I get what appears to be a series of inconsistant small blue sparks. Mixed in are much larger white flashes. So it's like this: small blue sparks pecking away - then big white flashes - small blue sparks peck for a while - then white flashes. It's not very consistant - it varys quite a bit. But this happens on ALL FOUR PLUG LOCATIONS.

Questions: Are the small blue sparks normal? Or is the colortune plug suppose to "glow" like the literature says. The white flashes look like a ring of color around the plug. The small blue sparks look like little pecks of sparks. I thought the ring of color was correct? And, I suspect these small blue sparks mean I have a weak spark?

Could this be a weak ignition coil giving too small of spark and gets worse after warmup? Would this explain why my engine runs better by disconnecting the vacuum hose - not a big enough spark to burn the gas so it runs rich?

BTW: Wires, cap, points and condensor were replaced this spring.

 

[Dave Russell]

[ QUOTE ]
I just purchased a colortune kit to try to find what is going on with my rough idle.

When it's cold the idle is not bad (not perfect either, but not bad). After warm up for say 20 minutes it gets very rough! Mostly in traffic, stop lights etc. If I disconnect the vacuum hose to the distributor - the engine runs much better - which leads me to believe I'm running rich for some reason?


[/ QUOTE ]
I personally think the Colortune is a joke - though many think it is wonderful. You can't really tell anything with the colortune without having a lot of experience. It is not much of a tool for troubleshooting, only fine tuning of an engine that is already nearly perfect.

From your observations I would agree that it is running rich. Concentrate on finding this cause.
D

 

[Jonnyc]

Dave thanks for the reply. Did you try the colortune before? Did you have small blue sparks, or did you have a glowing ring of color? I'm suspecting that my spark is too weak and gets progressively worse after warm up. What's your opinion on this?

 

[aerog]

I don't remember seeing a "glow of color" - you're looking at the actual spark of the plug and will see it flicker when at idle. Yellow should indicate rich, blue is lean, somewhere in the middle (blue/white I think) is just right. The problem is those colors might shift around a little depending on additives that are in your particular gasoline - at least that's what I've read. I set the two carbs on my MGB using colortune, and while it's interesting to see the colors I don't think it's necessarily that much better than using the "lift the pin" method of checking the mixture on SUs.

What carb(s) are you running on your engine? SU HIFs, HS4s, Zenith, Weber??

 

[Jonnyc]

It's a '71 all stock ignition and original HS4 SU's (rebuilt this spring).

Again, it's normal for the plug to produce mostly tiny little blue sparks with much larger bright flashes of white rings? I'm getting a lot of misfiring after warmup and the colortune is really showing what's happening in the combustion chamber. The plug flashes a bright white ring on every misfire. Thats what it appears like it's doing. But if I have a weak spark with surges of good spark then that would explain it too - right?

If a coil goes bad... could these symptoms appear?

 

[Jonnyc]

Replaced the coil - same problem. Rough idle and misfires. Colortune flashes bright white on every misfire.

What am I missing??

 

[Jonnyc]

The biggest question I have is about the small sparks I get - they just seem too small. Shouldn't it be a consistant pulsating "ring" of color rather than these little tiny sparks?! If the tiny sparks are correct for the colortune, then what are the larger rings of color that spashes in from time to time?? I guess at this point I'm using Colortune as a diagnostic tool for the misfire rather than the mixture adjustment. It's certainly showing that there is a misfire of some sort.

So anyway, I did remove the colortune and went back to the basics. I adjusted the mixture the old fashioned way by slightly pushing up the pistons - but again it's very difficult to adjust since the engine is bouncing around so much. Something is WRONG...

Replaced the condensor again with a spare I had. No effect. So far I have replaced the cap, rotor, wires, points and condensor a couple of months ago. Today, I replaced the coil, condensor (again). Yesterday I replaced the wires (again) and the cap (again). Checked the compression again today and all is around 150-155 on all 4. Dwell is 60, and timing is around 20 BTDC.

What the heck is left??

 

[Dave Russell]

[ QUOTE ]
Did you try the colortune before? Did you have small blue sparks, or did you have a glowing ring of color?

[/ QUOTE ]
Yes, I had a Colortune for quite some time. Found it amusing but not very helpful. Finally gave it to someone else. I know one guy that was so impressed with it that he bought one for each cylinder.

I think if you peer intently at it, in subdued light, & at exactly the correct angle, (very narrow correct viewing angle) you will find that you are seeing two different things. The spark itself - small & blue & the combustion flame, glow. What you go by for mixture tuning is the combustion flame color. It could vary from yellow - cold - rich, to normal - blue, to hot - white - lean. Supposedly blue is correct. As I say, it takes some experience to interpret what you are seeing & a whole lot of messing around to see everything. If you are looking "correctly" & see only sparks it means that that particular cylinder is not igniting, due to wrong mixture, no compression, or something else.

Probably a better way to check spark would be to put a timimg light on one plug lead at a time & check for spark regularity of the strobe. A shop with a modern analyzer could tell in a few minutes just how your ignition & plugs are functioning, & a lot more such as cylinder pressure balance.

Never discount plug trouble just because they are new. Years ago I fought an ignition system for quite a while & replaced plugs first, then coil, cables, & cap. In desperation I went to a "real" shop. The analyzer immediately showed that three of the new plugs were bad. When the guy tried to sell me new plugs I protested that they were new. He said it happens with "that" brand of plugs. If that was not the problem, he would put my plugs back in. Best $40 plus plugs I ever spent. Would have saved a lot by having it run on the analyzer in the first place. Since I was a confident do-it- yourselfer, I just knew that I didn't need pro help.
D

 

[Jonnyc]

Thanks Dave. Yes, I'm to the point where I need a professional.

Again, I must stress that I don't even think the colortune plug is "flaming" correctly at all. It's just very small sparks. A flame in the shape of a ring happens very inconsistantly. Mostly it's just little sparks.

I found this webpage with images of how it's suppose to look. Mine looks nothing like this. Tiny sparks instead of the pictured "flamed" ring of color.

https://www.surenet.net/~verhey/colourtune/Intro.htm

At this point I have a problem with my spark being inconsistant and too weak on ALL cylinders. Or I have a defective colortune.

I'm at a loss, so I will contact a shop next week.

 

[Jim1971]

What do your spark plugs read when the engine is smooth as to the reading when it is rough? I use the
Bosch platinum plugs and my engine seems to run smoother. My 1971 B does the same idle thing in traffic
when it is very hot outside. I do not worry about it. I hold my right foot on both the brake and gas to keep
the idle going. Back in 1971 I had a brand new B and it did the same sort of thing, but not as consistantly.
The dealer told me it was due to the carbs being above the exhaust manifold and the heat shield not being
very effective. The gas in the carbs, especially the rear one, gets too hot when the car is not moving.