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Could a leak under windscreen cause car to stall after rain?

Posted: Wed Dec 10, 2014 1:05 pm
by jonahnaylor
Hi I hope someone may be able to help.

This problem is annoying as 95% of the time my '78 MGB GT is reliable and starts first time and runs good. It's my daily driver and takes me everywhere.

But I keep noticing my Tach only works when I have the fan heater turned on or some other circuit, lights etc.

This doesn't really bother me, but sometimes for no reason at all when pulling up at a junction, roundabout or traffic lights the car will stall and I'll have to quickly restart it to avoid a queue of angry traffic behind!

At first I thought this was completely random and I've even had work done on the car since to fix a manifold leak and check other bits which I thought fixed it.

But after some heavy rain yesterday the car was stalling again. I then started to think is there a pattern; whenever there is a lot of humidity or rain this seems to happen and when it's dry everything works as it should...

This brings me to my second issue, I have a leak under the driver-side bottom corner of the windscreen - so when it does rain heavy I get a wet right leg from water dripping down behind the dash and the gauges.

Does anyone know if this could be the source of the problem - something behind the tach or near the gauges or wiring getting wet and shorting to cause a stall?

Any help would be really appreciated. For now I'm going to add some sealant to see if it helps at all.

Thanks again for any advise or checks I can do. The dizzy is dry, HT leads good, coil pretty new etc - I'm sure it must be some wet getting in somewhere...

Re: Could a leak under windscreen cause car to stall after r

Posted: Sat Dec 13, 2014 4:06 pm
by jonahnaylor
Just to update what I've tried so far:

1. Fitted a fuel filter before the carbs (whoever had the car before me had removed it so no filter was present).
2. Replaced the old Starter Relay and Ignition Relay black plastic units with new ones. I've read before these can cause intermittent running if corroded on the inside.
3. Checked the fuel pump is clicking and the contacts / terminals in the boot are clean and corrosion free.
4. Checked rotor cap is dry, HT leads and all connections are good and coil connections too.
5. Also added sealant to the windscreen leak and made sure everything was dry.

Took the car for a spin feeling confident and still the same problems. The car wants to stall as soon as you put the clutch in make a turn or come to a stop. The only way to keep it going is have a little bit of choke out all the time...

I'm not really sure what to try next!

Re: Could a leak under windscreen cause car to stall after r

Posted: Sun Dec 28, 2014 9:26 am
by jonahnaylor
A further update to the problems...

Ok so after rechecking if the SU HIF4 Carbs were balanced (or in sync) with a UniSyn tool, I found they had unbalanced a little. So I adjusted and after balancing them with the engine running and air filters still off I blasted the carbs and intakes with Carb Cleaner spray. Then revving it up and out lots and spraying loads more in there. After using about half a spray can of Halfords carb cleaner, the car was again ticking over nicely.

So out on to the road and more testing - when parking up back at home I had quite a lot of fuel coming out of the Carb vent / overflow pipes!! More carb cleaner again and now the fuel overflow leaks seem to have stopped too and the car is running great again.

Seems like a combination of small things (Floats in the carb sticking maybe?) along with other debris and dirt in the carbs - probably a result of not having a fuel filter previously. That coupled with being a little off balance I think was causing the stalling.

I'll update the thread if it reoccurs - which will probably mean a Carb Rebuild kit... But all is now well again at least for now! Phew! :D