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GaryBeu

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The non-mechanic.

My MGB runs great for a few days then runs rough. I've cleaned plugs and adjusted mixture. Running rough today and I found something I haven't seen before...Front plug and rear plug have the slight brownish color that seems to be about correct. The two middle plugs are both sooty black which says too rich. Would out of adjustment valves maybe cause that? I don't know anything about what the valve adjustment does. Thanks for any ideas/suggestions.

Gary
 
Bad valve seals etc. could cause that... When the valves are adjusted they should put news valve seals in to stop the oil from burning out all the time. What other problems do you have which could relate to the rough running?
 
Aged seals can be a cause, worn guides too. But renewing the seals in an MGB engine is not a task easily accomplished as part of a valve adjustment. As long as you're sure the middle two cylinders' in/ex valves have the proper lash (and are not too tight) it can be seals, guides or something like a manifold leak.

My first suggestion is to have a leak-down test performed, to determine what's actually going on.
 
Doc, Are you saying that a intake manifold leak could cause that sooting effect? Would that only be on the two center cylinders, or could that effect the outer two cylinders or any individual cylinder also? I know these little 4 bangers give you fits at times. PJ
 
PAUL161 said:
Doc, Are you saying that a intake manifold leak could cause that sooting effect? Would that only be on the two center cylinders, or could that effect the outer two cylinders or any individual cylinder also? I know these little 4 bangers give you fits at times. PJ
Click to expand...

A intake manifold leak could do that, because the air source is not continuous, but more so I see on MAF sensor cars that mix the fuel and air past the sensor...
 
It may even be a bad head gasket. Web between the center two holes goes and neither would hold enough combustion pressure to burn off the mix efficiently...
 
GBlearner said:
PAUL161 said:
Doc, Are you saying that a intake manifold leak could cause that sooting effect? Would that only be on the two center cylinders, or could that effect the outer two cylinders or any individual cylinder also? I know these little 4 bangers give you fits at times. PJ
Click to expand...

A intake manifold leak could do that, because the air source is not continuous, but more so I see on MAF sensor cars that mix the fuel and air past the sensor...
Click to expand...

The MGB intake is 'siamese-ported' inside the head, so it would be less likely the manifold than the head gasket or valves/guides/seals.

With Gary & Carla's car they have twin SU's. If the front two cylinders were different than the back two we could blame carbs. Not so much with two middle holes different than the ends.
 
Well, it's been a busy few weeks around here with "things" to do :smile:!

Finally seem to have Ellie (MGB) sorted out. Adjusted valves, replaced burned points, gapped plugs, checked plug wires,adjusted carbs, etc. Been driving a lot for about 5 days and she is running like a dream. Hopefully, this will continue for awhile.

All of the help and ideas from "the forum" makes this an incredible place to visit. Carla and I really appreciate the patience you all exhibit with us. Once again, THANK YOU ALL VERY MUCH !!

Gary and Carla
 
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