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MG TD TF 1500 - 53 MGTD Sooty Plugs Cyl 1 and 3

Greetings,

I have 53 MGTD, the problems is that the plugs for cyliners 1 and 3 are very black and sooty, while the other plugs are "normal, grayish brown" color. The starts fine and runs with excellent power until after about 40 minutes, it begins missing and is very sluggish.

It has the Pertonix system, checked and adjust the the valve lifers, checked and adjusted the mixture and the idle, tends to run about 1000rpm. Wires were changed out and firing order has been verified. I am thinking that the one SU carb needs adjusted OR that the rings /values for these two cylinders need replaced. Any other thoughts?


P Trautmann

How are the compressions?
Steven Tobias

Strange that all is well until you've been running for 40 minutes...and that one spark plug per carburetor is fine. Other than compression everything that affects one cylinder affects all the others. Have you tried swapping plugs (1 to 2, 3 to 4) and seeing what happens?
Gene Gillam

Since 1 and 3 run off of different carbs, and 2 and 4 are o.k., then I would look at the valve adjustment for 1 and 3....
Edward
E.B. Wesson

Firing order in these engines is 1-3-4-2, so if the distributor spindle or bushing were worn, and did wobble, perhaps it can affect two next (in firing order) cylinders, like 1 and 3, producing a weaker spark or different ignition timing. This would be probably worse in plain systems with points (yours seem to be an electronic system without points).

One way to check this condition is to rotate the distributor body by exactly 90 or 180 degrees and changing the spark plug wires correspondingly. If the problem appears in other cylinders, this would be the cause.

Jesús
J Benajes

Not saying this is the same as your situation but, I had a similar problem with our 72 MGB that has a totally rebuilt engine and thought it was the carbs, so I had them rebuilt. It didn't solve the problem. I sent the distributor out to Advanced Electronics, had it rebuilt with points as original and I could not believe the difference. The engine never ran so good. I'm not a believer in the conversion electronic ignition systems and think their very over rated. Too many people have had issues with them. The rebuilt engine in my TF has a point distributor and is the sweetest running engine I've heard in a long time. Just another thought to throw your way. PJ
Paul J

Sorry, I meant to say Jeff at Advanced Distributors, not electronics. PJ
Paul J

Thanks all,

FYI..the compression is good on Cylinders 1,4,2 and slightly less on #3. Adjusted gap on the valves so all are .019, 3 were too tight.

Going to trouble shoot the distributor, did check the cap for 'lighting" streaks, found none. Had to replace the resistor for the Petronix, it was cracked. Going to investigate going back to an orginal distributor.

Will keep you informed.
P Trautmann

Why 019? Your car came with an 012 cam, and John Twist sets hi2011-06-14
t lange

How are the compressions?
Steven Tobias

Strange that all is well until you've been running for 40 minutes...and that one spark plug per carburetor is fine. Other than compression everything that affects one cylinder affects all the others. Have you tried swapping plugs (1 to 2, 3 to 4) and seeing what happens?
Gene Gillam

Since 1 and 3 run off of different carbs, and 2 and 4 are o.k., then I would look at the valve adjustment for 1 and 3....
Edward
E.B. Wesson

Firing order in these engines is 1-3-4-2, so if the distributor spindle or bushing were worn, and did wobble, perhaps it can affect two next (in firing order) cylinders, like 1 and 3, producing a weaker spark or different ignition timing. This would be probably worse in plain systems with points (yours seem to be an electronic system without points).

One way to check this condition is to rotate the distributor body by exactly 90 or 180 degrees and changing the spark plug wires correspondingly. If the problem appears in other cylinders, this would be the cause.

Jesús
J Benajes

Not saying this is the same as your situation but, I had a similar problem with our 72 MGB that has a totally rebuilt engine and thought it was the carbs, so I had them rebuilt. It didn't solve the problem. I sent the distributor out to Advanced Electronics, had it rebuilt with points as original and I could not believe the difference. The engine never ran so good. I'm not a believer in the conversion electronic ignition systems and think their very over rated. Too many people have had issues with them. The rebuilt engine in my TF has a point distributor and is the sweetest running engine I've heard in a long time. Just another thought to throw your way. PJ
Paul J

Sorry, I meant to say Jeff at Advanced Distributors, not electronics. PJ
Paul J

Thanks all,

FYI..the compression is good on Cylinders 1,4,2 and slightly less on #3. Adjusted gap on the valves so all are .019, 3 were too tight.

Going to trouble shoot the distributor, did check the cap for 'lighting" streaks, found none. Had to replace the resistor for the Petronix, it was cracked. Going to investigate going back to an orginal distributor.

Will keep you informed.
P Trautmann

Why 019? Your car came with an 012 cam, and John Twist sets his at 015 to be on the safe side. Is your valve train noisy? You may have some bad cam lobes.

Tom
t lange

PT,
How old are the plugs??? Are you driving robustly for the 40 minutes? or is it more of a "parade" engine speed which might allow the plugs to carbon over.
SPW
STEVE WINCZE

PT,
How old are the plugs??? Are you driving robustly for the 40 minutes? or is it more of a "parade" engine speed which might allow the plugs to carbon over.
SPW
STEVE WINCZE

Greetings,

Been on vacation while the MG just sat there. Here what is happening now. Re-adjust cams back to orginal specs, valve train is working great. Compression on all four cylinders is good. The car has the pertonix ingition system. After some reseaching, came to the conclusion that the spark plugs (champion L86C) were not buring all of the gas, all were wet black and sooty though some more than others. Purchased NGK B6ES install them, check the distributor as well. The car was slow to fire but roared to life, rmp at idle 18, with the old plugs was about 900 after my brother adjusted it. Drove the car for about 40 minutes, some stop and go, ran it 1/4 mile at 50 and engine was strong and smooth.

Returned home. turn off the car. Did some detailing, minor, went to start the car and it would not start. It would turn over but no fire, did flood it by accidented, waited, and attempted to restart. 4 hrs later, I pulled the plugs, they looked great, grayish with little to no black soot. Reinstalled, attempted to start no luck. Put the old plugs back in car, it started, ROUGHLY. I drove it around the block, getting the RPMs up but ran as it did before, hesitating, lots of carbon out the exhaust.

I am out of ideas, anyone have some?

Pete
P Trautmann

Greetings,

Been on vacation while the MG just sat there. Here what is happening now. Re-adjust cams back to orginal specs, valve train is working great. Compression on all four cylinders is good. The car has the pertonix ingition system. After some reseaching, came to the conclusion that the spark plugs (champion L86C) were not buring all of the gas, all were wet black and sooty though some more than others. Purchased NGK B6ES install them, check the distributor as well. The car was slow to fire but roared to life, rmp at idle 18, with the old plugs was about 900 after my brother adjusted it. Drove the car for about 40 minutes, some stop and go, ran it 1/4 mile at 50 and engine was strong and smooth.

Returned home. turn off the car. Did some detailing, minor, went to start the car and it would not start. It would turn over but no fire, did flood it by accidented, waited, and attempted to restart. 4 hrs later, I pulled the plugs, they looked great, grayish with little to no black soot. Reinstalled, attempted to start no luck. Put the old plugs back in car, it started, ROUGHLY. I drove it around the block, getting the RPMs up but ran as it did before, hesitating, lots of carbon out the exhaust.

I am out of ideas, anyone have some?

Pete
P Trautmann

Major issue jumps out at me: The Champion plugs are 1/2" reach for the early heads, and the B6ES are 3/4" reach. It is very bad to have the long plugs in the short plug head. Have you changed the rotor? Preferably for one of the red ones. See the archives- many, many failures. Caps can fail and look perfect. Make sure the plug wires are actually seated fully into the cap- easy to pull one loose.
George Butz

PS- long plugs in the short head are bad for two reasons: they can hit the piston top or a valve, and carbon will build up on the exposed threads and you won't be able to remove them.
George Butz

Replaced plugs with champion l90c...start fine ..ran for 20 minutes and died..will not restart...checked coils..good current to distributor...weak to no current coming from plugs..ordered a new pertonix ignitorwhat else can I do?
P Trautmann

Rotor????
George Butz

You said your coil is good, how did you test it?
If the problem persists , with the new pertronix, then the problem pretty much has to be either the coil, or the coil wire....Something has to be keeping the plugs from getting fire....

You are getting good, clean fuel supply, and proper carb adjustment, right?
Edward
E.B. Wesson

"Had to replace the resistor for the Petronix". What resistor? Is yours a negative ground or a positive ground system? Bud
Bud Krueger (TD10855)

I installed a new distributor cap and rotor, tested current flowing through wires by 1) checking for spark from plugs, holding it close to engine block while turing over enging while plugs were still attached to distr wires (little to no spark), 2) tested wire from coil to distrib by removing end from distrib and holding it close to engine block ( good strong spark, much stronger than plugs)

Good clean fuel and both carbs are functioning and adjusted.

The car has a positive ground.

I did not install the pertonix intitally.

Thanks for all the tech support.
P Trautmann

It might be worth your while to have a look at the Pertronix info on my website
http://www.ttalk.info/Tech/pertronix_igniters.htm , especially the instructions for installing a positive ground unit -
http://www.ttalk.info/Tech/PerPosGndWiring.htm. Is yours wired that way? Bud
Bud Krueger (TD10855)

Bud..thank you for the info...after closer inspection the coil's resistance was a consistent 4.2 0hms
.relaced the coil, engine roared to life and have put 50 miles (both highway and side streets)...thank you again
P Trautmann

This thread was discussed between 14/06/2011 and 24/07/2011

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