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MG MGB Technical - Water gets into the dizzy whilst driving in rain.

Twice now this has happpend while driving my '72 B-GT during heavy rain. The first time it died completly and I had to have the wife come and tow me home. This last time it started to faulter, sputter and would die if I let off of the throttle. I was able to get it home as long as I kept the revs up. But it was running really rough.

Is this a common problem. I really have only driven the GT these two times in heavy rain. My '79 MGB has been driven in heavy rain with no ignition problems. The GT has a 25D4 dizzy and the '79 B has a 45D4.

I've noticed that I could pull the cap away from the dizzy body about a 1/4 inch even with both of the clips in place. Is this normal? I have thought about wraping some electrical tape around where the cap and dizzy body meet up. What do you think?

John Fraioli
John Fraioli

John, did you look under the cap when you got it home?
I bet it was dry,but how about the wires and the outside of the cap? My quess pretty dry maybe a little
"Misty". the quick thing to do is change the cap/roter and wires, if you want to have some fun take an old spray bottle
an empty windex bottle works well fill it with water and with the car all warmed up on a sunny day open the hood and while the car is idleing mist the cap and wires it will start to run rough maybe even stall,for fun on a greater scale, set it up outside at night with a good droplight, run the car,spray the cap and wires and turn out the light as the car starts to run rough check out the light show.
just a thought, let us know how it works out.

RIC
RIC LLOYD

John,

This isn't normal, no. You should not be able to pull the cap away from the dizzy with both clips on so that won't help. As Ric says, though, you're probably having trouble with leaking HT leads as the dizzy is actually quite well protected from rain. When they age the insulation breaks down, allowing the HT current to leak away to earth when damp instead of jumping the gap in the spark plug. Change the leads, points, rotor arm and cap - it will take no more than half an hour (5 minutes if you just change the leads and cap) and cost very little. Carry a can of WD40 or some other water dispersent - next time it happens spray the cap and leads and it should get you home. Finally, an old Mini trick if you find you do get water in the dizzy. On the Mini the distributor is at the front right behind the radiator grille (and the radiator is side-mounted so there's little protection other than a cardboard shield). Take a washing up glove, cut the ends of the fingers off and feed the HT leads through each finger hole. Pull the body of the glove down over the distributor cap. You now have a virtually free, bright yellow, waterproof rubber distributor cap seal!

Cheers,
Tim
T Jenner

I have had water flooding into the footwells but the sparks kept on flowing to the plugs. So no, not usual on the B. I did have a Mini Cooper and that was fitted with the factory boot on the dizzi, again no problems in the rain.
Stan Best

Just wondering if you have the correct distributor cap, no way you should be able to move it at all with the clips in place!
Eric Martin

Hi John,

I suspect your dizzy is getting wet because the heater valve is leaking, which is immediately above the dizzy. Get yourself a new heater valve. I'm sure that will cure the problem.

Good luck.

willyphixitt
W A Nixson

I started writing that but thought "No, surely he wouldn't have said it only happened in heavy rain if it didn't" ... would he?
Paul Hunt

Just covering all bases, Paul. Maybe the heater has only just been turned back on. That was my thinking.

Will have to wait for John to reply.

willyphixitt
W A Nixson

On a related note, if the top hose is leaking water can be blown back onto the HT leads and distributor when moving causing a nasty misfire - had that before! Not sure if it's possible on all models though, as I can't remember if the position of the hoses altered as the radiators changed.

Cheers,
Tim
T Jenner

This thread was discussed between 12/10/2009 and 16/10/2009

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