Air filters causing rough running ??

Steve,
Good advice! I'm in the software business and if I have a dollar for each time a developer changed a bit of code and the system stopped working then claimed that his change would never affect that area!!
I think a new set of plugs and leads is a good idea, I have also just won a garage standard emissions tester on e-bay for about $150 (ú100 uk) so that should help! Mine is a 73 S3 with four pipes? so I can find the right bank, thanks for the tips.
It could well be one lead did fail, I have a timing light so I'll try each pot in turn, I did do a resistance check on each lead and there was continuity but the resistance did seem high on most leads and did vary with the length (They are supressing leads on mine)
I'll keep you posted, I've decided to strip doen the smoking side as well but I'd like to sort the rough running first, don't want to confuse the issue with many tasks at one
Cheers
Shaun

Shaun,

I'm not sure what year your car is, but on a Series 3, you will either have 2 or 4 outlets on your fantail ('71/2 were 4 outlet, '73/4 were 2, I believe). If you look at the exhaust system, each bank runs to an exhaust pipe (dual exhaust) which runs back to a resonator under the rear. The fantail is mounted on the resonator. If you have a 2-outlet fantail, the left is the left bank, the right is right. If you have 4, the two left outlets are the left bank and the two right ones are the right side. You can measure each bank's emissions in either of the outlets for that bank on the 4 outlet fantail.

I have not used a Colortune, but I've read posts by others who have and say they work well, if you know what you are looking for.

If your wires and distributor cap and rotor are "a few years old", I'd go back and check the wires again. If you are not careful removing the wires from the plugs, it is easy to detach or loosen the connector from the wire or the carbon core, depending on the type of wire you have. If this happens, it can produce an intermittent spark or no spark at all, causing your rough idle. Did you try checking the wires for continuity with an inductive timing light like I'd previously suggested?

When you removed them, were you careful to grasp the boot and work the connector loose from the plug, or did you grab the wire and pull? If you pulled on the wire or on the boot without grasping the connector itself, you could have pulled the wire loose or broken it at the connection. Also, putting them back, did you make sure they actually "snapped" home on each plug? There is a corrollary to Murphy's Law that says that if you made a repair and things got worse afterwards, look to what you did, not something else for the source of the problem. And if the plugs are 8000 miles old (more than a few years, I assume), I'd consider putting new ones in. I'd go for the NGK's if I were you, with new wires, distributor cap and rotor. IMHO.

Good luck. I think the other things your looking at are certainly things that should be looked at. But since this all started when you cleaned and gapped the plugs, I'd look there first, like I said before.

Regards,
Steve Weinstein, JTC-NJ
'72 E-type 2+2
'89 XJS Coupe

Steve,
Thanks for the speedy input, I have just bought a carb balancer kit from Gunsons which I hope will do the job. I take your point on the air filters I doubted if it should make any differance but it seemed to, maybe I was just at the end of an afternoon trying differant things and wanted it to sound better.
I'll balance the carbs when it arrived, I think they are out of balance as the hiss from one bank does seem less, this may cause rough idle I guess and one side or part of one side may be getting less fuel/air into the chambers.
I'll look out for an exhaust gas analyser, e-bay have a few, you mention that you can check each bank seperatly, does the back fintail box only split the two side into seperate final pipes (if that makes sense). In which case can you place the analyser down into the respective exhaust of the left and right banks. Have you ever used a colortune, I've heard mixed responses, some say great, some say rubbish.
Do you have a part number for the needle adjuster?
I've checked all of the vacuum tubes and they seem fine, when I disconnected the adv/ret one the revs rose and if I sucked into the tube it dropped so it would seem to be working (I also check with the dist cap off).
I also found out the plugs are about 8000 mile sold so they should be fine, a new set of leads a few years ago with a new dist cap.
I'll keep you posted as to the 'saga'
Cheers
shaun

Shaun,

I don't think you air filters are causing your problem. Unless they are completely plugged (which would be obvious to the naked eye), they should not restrict air flow enough to interfere with performance. That, after all, is the whole point -- they filter dirt from the air, but let enough pass through so the car runs properly. Never hurts to change them, though.

As far as balancing goes, you don't put your ear to the carbs. The "sound" method involves taking a length of garden hose, about 2' to 3' long, putting one end of the hose into the mouth of the carb and holding the other end to your ear with a cupped hand. It's like a stethoscope. You move the hose from carb to carb and back again, listening for the sound to be the same intensity. This is a very inexact way to do it.

A much better method is to us a Unisyn. Simple little device, not expensive, that fits over the opening of the carb, with a little tube sticking up with a red ball inside. You adjust the Unisyn to the first carb so the ball is mid-way up the tube. Then move it to the next carb and see if it is at the same level. You adjust the carbs, both sides, until all 4 read the same on the Unisyn.

As far as richness goes, the amount that you can adjust Zenith Stromberg cards is minimal. You will need the special tool to adjust the needle in the piston. Not expensive, but get it. To make the adjustments properly, you will, however, need an exhaust emissions analyzer. It is the only accurate way to tell if either bank is running rich or lean, and to be sure they are both adjusted the same. I'd suggest balancing the carbs first, set the idle, check balance again, adjust if necessary, check emissions, adjust needles if necessary, check and reset idle, then check and reset balance.

If you're still having problems, I'd go back and recheck the basics, and make sure all of your vacuum lines are fitted properly.

Good luck,
Steve Weinstein, JTC-NJ
'72 E-type 2+2
'89 XJS Coupe