cyl. 5&6 spark plugs sooty.

[Malcolm Clarke]

To all intensive purposes my CP TR6 it runs fine. But I notice that the spark plugs in cyl 5&6 appear sooty. Reading other posts on the forum I get the impression that this is not exactly a unique situation.

Is there a reason why this should be, shall we say not an isolated occurrence. Is it to do with a quirk in the design of the fuel system. ?

I have now tried using NKG BP6ES in cyls 1-4 and BPR5ES in cyl 5&6 but the situation is much the same.

[John L]

I think you need to check the air flow for 5 6 first of all, compared to the the other 4 inlets, it just maybe the throttle butterfly is not opening, or the bush on the throttle shaft id missing, which doesn't allow the butterflies on 5 and 6 to open properly.

John

 

[Andy Moltu]

At tickover the rear 2 cylinders tend to run rich. (Furthest from the air inlet and most warmed by the heat in the engine bay/exhaust manifold)

The best way to do a plug chop is to drive the car for a few miles, and cut the engine and freewheel to a lay by. Then check the plugs.

If 5&6 are still sooty it may be the throttles are out of balance.

[Jonny TR6]

A wiser man than me told me you could fit an air mixture screw at the end of the inlet manifold next to 5&6, so you have one at either end. Apparently it makes the idle much smoother and better all round running ?

Not seen anything on this, but must admit, I haven’t looked.

Edited May 1, 2023 by Jonny TR6

[Malcolm Clarke]

Freewheel to a suitable lay-by sounds a sensible idea.  
 

[Adrian Steele]

On 5/1/2023 at 9:18 PM, Jonny TR6 said:

A wiser man than me told me you could fit an air mixture screw at the end of the inlet manifold next to 5&6, so you have one at either end. Apparently it makes the idle much smoother and better all round running ?

Not seen anything on this, but must admit, I haven’t looked.

I met a German, or might have been Dutch TR6 owner a couple of years ago in deepest West Wales (middle of nowhere) and being nosey I had to have a look at his car; he also had a second air mixture screw which he’d fettled and swore by it’s effectiveness. Surprised that TR Trader or other hasn’t started marketing such an upgrade. 

[Jonny TR6]

Looking at the inlet manifolds, would a perfect solution be an individual bleed screw on the top of each manifold, where the vacuum take offs and blanking cap are and do away with the one on the right ? That way each bank of 2 cylinders gets the same flow of air at idle. You’d obviously need to factor in some means of vacuum take off, but to my simple brain it would work.

Interested in the collective brains and wiser sages than I thoughts on this ?

Edited June 20, 2023 by Jonny TR6

[KiwiTR6]

4 hours ago, Jonny TR6 said:

Looking at the inlet manifolds, would a perfect solution be an individual bleed screw on the top of each manifold, where the vacuum take offs and blanking cap are and do away with the one on the right ? That way each bank of 2 cylinders gets the same flow of air at idle. You’d obviously need to factor in some means of vacuum take off, but to my simple brain it would work.

Interested in the collective brains and wiser sages than I thoughts on this ?

If the rocker cover breather is still connected to the air intake tube then that is the most likely cause of the 5&6 issue.  Removing that and connecting it to a catch tank or capping it with a small filter as I have done will fix it - see my plugs as proof (a little rich, but all the same).

 

[Mike C]

I've used BUR6ET's for years and they just keep firing , even when they look sooty.