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MG MGB Technical - Where's the moisture getting in?

Every time it rains, it's the same story. Somewhere moisture is getting in and the car runs rough on startup. As it warms up and dries out the problem disappears and it's smooth sailing.

I put in new spark plugs and wires, new Petronix Distributor. Problem remains. Everything is new and tight. What else could be causing it?
Bernie Lowe

What's the car? Louvered bonnet??
Allan Reeling

Was the cap replaced as well? They become porous, over time, and should be replaced on an annual basis. Also, a lot of the caps, on the market today, are of poor quality and fail after a short time in service. I would substitute a new cap and see if it remedies the problem. RAY
rjm RAY

Condensation ? Barrie E
B Egerton

The heater control valve can leak and is perfectley positioned to spray the dissi
Stan Best

Thanks for the input gentlemen.

Stan - if it was the heater control valve the problem would happen randomly, but this only happens when it's rainy.

Ray - I thought it might be a lousy cap on the new distributor so I replaced that too with another new one. Next wet day - same issue on start till it warmed up.

It's a puzzle. Moisture is getting in somewhere and it is definitely appears to be weather related.
Bernie Lowe

Bernie,

See if you can catch it doing the rough run when it is dark. Then watch to see if you can see any sparks under the hood.

Charley
C R Huff

A couple of things come to my mind. How is the water getting past the hood? Are you parking outside. If so, next time it rains can you park it under cover? Then does it still have starting issues?
Another thing to try is while it’s parked in it’s normal spot, next time it rains, before you start it up take a look under the hood, do you see any water/moisture, check under the dist cap, see any moisture.
Just things to try.
Good luck
MGBV81

If the coil has been abused by bad wires, rotor, very wide plug gaps, etc, it may have tracked between the HT tower and one of the LT terminals. Again, look at it in the dark & damp. Or take it off and examine under magnification. If it has a problem in the damp, it will get worse until it has the problem all the time.

FRM
FR Millmore

I'm with FRM
Have a good look around the coil tower for burn marks and pinholes, is it clean, and also when you replaced the plug leeds did the coil leed get replaced
Also pull the plugs out and have a good look at the external insulators , sparks could be tracking down the outsides of these - if so there will be little black lines as if someone has drawn down them with a pencil.
If this is the problem, clean them up or replace them and give them a coat of dielectic grease.
It's a fairly common happening if there is a high performance ign. coil involved.
Willy
William Revit

Check the car's earth strap

Rgds Trevor
t burnett

"Check the car's earth strap"

Eh?

No matter what coil is used the peak actual HT voltage is governed by the plug gaps. It is only if these are opened up too much, perhaps if one does have a high-voltage coil or even without, that you may get HT breakdown.
PaulH Solihull

This thread was discussed between 20/05/2011 and 27/05/2011

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