Intermittent power loss 1975 rb roadster

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Vic Butler
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Re: Intermittent power loss 1975 rb roadster

Post by Vic Butler » Mon Apr 08, 2019 4:27 pm

Paul, if it was a fuel problem the engine would not cut out dead. It's an ignition problem.
There is one thing I might suggest
Disconnect the tacho supply lead from the coil and see if it still cuts out. Just a thought that the fault could be in the tacho.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine

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Paul Hollingworth
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Re: Intermittent power loss 1975 rb roadster

Post by Paul Hollingworth » Mon Apr 08, 2019 4:58 pm

What about your coil, I had similar issues with a Mini many moons ago, turned out to be that.
1971 MGB roadster & 2006 MGTF

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Charles Farran
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Re: Intermittent power loss 1975 rb roadster

Post by Charles Farran » Mon Apr 08, 2019 5:39 pm

Hi Paul,
Further to Vic's & Paul H's comments ,If the tacho dies immediately when the engine loses power / cuts out this suggests an electrical problem rather than low fuel / no fuel supply to the carbs/ engine. Have you checked to see if the pump clicks when the ignition is switched on?
(Much simpler to check the electrical side first before dismantling the pump). Have you got a spare ignition relay you can substitute as they are notorious for causing intermittent faults? I appreciate you changed /cleaned all the connectors, but from my own experience i have found they might have worked loose if not completely pushed home when reassembled.
Cheers,
Charles
1980 Roadster

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Charles Farran
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Re: Intermittent power loss 1975 rb roadster

Post by Charles Farran » Mon Apr 08, 2019 6:21 pm

Hi Paul,
Looking back over the history of your power loss, i realise i had forgotten that your car's electrical circuit was before an ignition relay was added separately from the starter relay.I would still be suspicious of the LT side if the tacho died immediately when the engine stopped, otherwise there would be a gradual drop in revs even if the car had stopped firing. Condensers can play up but tend to work or not work althougth some think when they get hot they start playing up. (worth changing to eliminate this as the cause) Have you checked that the new earthing wire within the distributor hasn't worked loose or got the insulation got chafed by the points / base plate?
Cheers,
Charles
1980 Roadster

Vic Butler
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Re: Intermittent power loss 1975 rb roadster

Post by Vic Butler » Mon Apr 08, 2019 7:05 pm

Like Paul H I had an intermittent cutting out on my Land Rover decades ago. It manifested itself on right hand cornering but came back to life when straightening. Quite by accident I touched the coil after a drive and it was too hot to touch. Changing it cured the problem but there is no tacho on the vehicle so I couldn't confirm whether it is the same fault. It would be worth changing the coil as it's not an expensive item but make sure you get a ballast resistor one.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine

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Paul Scott
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Re: Intermittent power loss 1975 rb roadster

Post by Paul Scott » Mon Apr 08, 2019 8:43 pm

Thank You all for your comments.

I'm going to hopefully take a look at some bits and pieces tomorrow.

I'm afraid the old technology is new to me. But I'm hopefully learning slowly - very slowly...

Looks like I'm limited to 50 mile drives before discovering if I have actually cured the issue. Next good run is Drive it Day via Hagerty drive into Bicester. 25miles to starting point - then 70ish from Porsche to Bicester. Wish us luck ;0)

I guess time will tell unless something is mega obvious once I start looking.

Obviously I will let you know how it all goes. Thanks again for the info.

Regards
Paul
1975 MGB Roadster
Webguru for MGB Register

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Paul Scott
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Re: Intermittent power loss 1975 rb roadster

Post by Paul Scott » Tue Apr 30, 2019 9:29 pm

Hi everyone,
Here is an update

I might have actually cured it!!

After fitting a tell tale light across the coil which went out when the tach & engine died for the same few seconds. Stopped - popped the bonnet and moved the negative to the chassis. Next time it died the light stayed on. So when I got to my destination I took out the "Lucas" condenser that I had already replaced and popped in a dizzy doctor condenser. 2 weekends later & 450 miles covered no more cutting out!!

Thanks again for your thoughts on this issue.

Regards
Paul :0)
1975 MGB Roadster
Webguru for MGB Register

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Charles Farran
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Re: Intermittent power loss 1975 rb roadster

Post by Charles Farran » Tue Apr 30, 2019 11:15 pm

Hi Paul,
That's great news. These cars can be frustrating at times, but give a tremendous feeling of satisfaction when you find the answer to a problem !
You won't be the last to fit a replacement part , only to find that the replacement part isn't performing as it should.
Until the next time........
Cheers, Charles
1980 Roadster

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