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Process of elimination.....are we having fun yet?

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My TR6 (triple ZS carbs) has been running too rich (black, sooty) plug on #3 cylinder. I leaned the middle carb, which feeds the 3 and 4 cylinder, and got no improvement. Gotta be something in the valves that won't allow complete combustion. Bad wire? Guess I have to go through the system step by sep to see why this is happening. Compression is 150 across. Any other thing that would cause one plug to burn bad? Has anyone out there in LBC-land ever had a season of near-perfect tune and enjoyed their baby without constant tuning. I think I am having fun. I think.

Bill
 
Bad wire, bad distributor cap (check for cracks,) bad plug...Also check your timing and advance.

Also make sure you have enough oil in the carb (piston dampening oil.) You can always try a thicker oil in that carb to see if it is just running richer across the board.
 
Re: Process of elimination.....are we having fun y

Bill,
Try swapping the plug then the wire on 3&4 to see if the problem reoccurs. First swap the plug, if this doesn't show the problem swap the wires. It's a simple test that will eliminate the obvious.
One other thing, you say the plug is sooty but is the engine missing or running rough ?
 
Re: Process of elimination.....are we having fun y

I posed a similar question about the ZS setup ('75 XJ6) in the Jaguar forum. I was getting black soot/backfire from the rear carb. I believe that the general answer is that the compression check should rule out the burnt or stuck valve possibility. I think everyone is on track with the ignition wire testing. You may talk to Jack Farrington in the Jaguar forum. He's always got a great troubleshooting procedure for problems like yours. My first thought would be the wire swap as well. Best of luck.

Brian
 
Re: Process of elimination.....are we having fun y

Hello Bill,
if the number three is black and dry, then it doesn't point to an electrical fault. (By the way thicker oil will richen the mixture on acceleration, but has no effect at steady throttle)
I would suggest checking the valve clearances, and while you do that compare the valve opening distances in case you have a worn lobe. The other thing that gives an apparent rich mixture is oil burning, although the plug tends to be 'wetter' than if it is excessive fuel. Also what was the engine doing prior to you checking the plugs, if it was after an idle do a full power high load check and see what that is like.
Incidentally, an easy electrical check for a plug is to clip your strobe light to that lead and see what it is doing.

Alec

P.S. I run my Triumph as an everyday car and don't need touch it between 3,000 mile services, and even then rarely need to alter the tuning, (2.5 P.I. engine on points.)
 
Re: Process of elimination.....are we having fun y

Pull the plug wire from the DISTRIBUTER while running. If you get a substantial change then the cylinder is not firing. You can also see the color of spark at the distributer.
 
Re: Process of elimination.....are we having fun y

Hello Skikir,
don't you mean that if you get a substancial change that cylinder is firing. Why disconnect the distributer end?

Alec
 
Re: Process of elimination.....are we having fun y

[ QUOTE ]
Hello Skikir,
don't you mean that if you get a substancial change that cylinder is firing. Why disconnect the distributer end?

Alec

[/ QUOTE ]

I think he meant it will change if the plug is firing. You pull the distributor end so that you don't have a wire charged with 30k/40k/60k volts in your hand. /ubbthreads/images/graemlins/troll.gif
 
Re: Process of elimination.....are we having fun y

Hello Hayfever,

that is what I thought. But pulling the wire from the distributor end does not guarantee that you will not get a shock. It is safer to use insulated tools to remove plug leads.

Alec
 
Would ya'll believe a bad distributor cap, a micro crack in the wrong place. I go through these things like I change my socks! I generally keep a half dozen on hand for things like this. They just don't make'em like they used to.

She runs like a champ now.....

Bill
 
Correction, it was bad plug wires all along. I had NAPA 7mm carbon wires, changed to Taylor 8mm braided, low resistance solid copper wires and THAT was the problem all along. Now she runs better than ever.

Bill
 
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