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MG TD TF 1500 - Dirty/soty carbs

During prep for engine/tranny removal, I have removed the cabs from the manifold. Upon removal, I discovered that both the manifold and the carbs are very sooty.

The car ran very well before this project but it would seem that there should be a lot less soot. Are the carbs too rich? What else could cause this condition? Thanks, Tom
Thomas McNamara

Lots of possible reasons: too rich due to incorrect or worn needles and/or jets, worn cork jet gaskets, incorrect mixture adjustment, incorrect fuel height, mis-matched pistons and chambers, choke not returning all the way, bad condenser, etc. etc. Haws your car been idling for a long time?

Tom Lange
MGT Repair
t lange

The car idled and ran well getting about 25 mpg overall. It has an mga rear end. The carbs were rebuilt by joe curto about about 6 years and 20,000 miles ago. I guess I will send them back to him?
How long does a rebuild last? Tom
Thomas McNamara

Joe is THE SU guy. I can't imagine the carbs would need a rebuild already. My first guess would be that the carb mixture was set to rich.
D. Sander

tom, are you saying the carb throats and intake manifold are sooty or the exhaust manifold is sooty? regards, tom
tm peterson

Air and fuel only go through the manifold and to the engine. Whether it ran rich or lean doesn't create soot. Backfiring and "eight-stroking" will. Check your spark plug ceramic color as one of your best clues.
I can't recall tearing down any engine with years of running that isn't somewhat black from the butterfly all the way down to the valves.

Four stroke engine cylinders can "eight-stroke" (2 strokes can 4 stroke) at idle, often showing up as a slight miss especially cold... a condition where the engine fires every other cycle. We all know that the cam events are advanced for running at higher rpms, so the intake starts to open during the exhaust cycle while the piston is still rising, and the intake is at a vacuum.
At idle, there's enough lingering pressure in the cylinder to blow exhaust out the intake valve, and thus it reinhales that exhaust gas and doesn't fire. Since it didn't fire, there's no pressure on the next cycle to blow exhaust out the intake, therefore, it can inhale fresh air/fuel and then fire. Black residue from this exhaust is nothing to be concerned about.

Hey all, the carb throats and intake manifold are sooty. Perhaps there is nothing to be concerned about? I'll check the plugs this evening. Tom
Thomas McNamara

Gunk on the intake track could be from fuel deposits, non-functional air filter, etc., unless running pretty badly, I don't think it would be from spitting back into the carbs. Maybe just modern fuel gunk? If it was running well, may be best to leave alone? George
George Butz

hey all. IWonder. if the manifold to head gasket is blown between cylinders 2& 3 some ofthe exhaust will escape through the carbs
Wright or? Just a thought
Yhoraalf. Norway TD4490.
Thoralf Sorensen (TD4490)

This thread was discussed between 19/01/2014 and 20/01/2014

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