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Good News ...and niggles (ignition?)

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ThomasH84 Avatar
ThomasH84 Thomas Horsley
Woolton, England, UK   GBR
Thanks again guys for all your input and help.

Did some more testing today. Coil is fine - it’s getting a good 9.9v when cranking both cold and warm. 12v when running as it should be for this model. Resistance is also fine at 3ohms.

I’ve ordered a new dizzy cap and red rotor. Also bought some new fuel hoses for the carbs (ethanol proof ones) as well as some heat shield tape in case it’s a vapourisation problem

Hopefully will be back alive for the wkend. The engine is sounding v strong and read to go...

Hope you’ve all had a fun wkend out and about in ur MGBs - or under them lol

Edited 1 time(s). Last edit at 2017-10-12 09:41 AM by ThomasH84.

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JIMBV8 Avatar
JIMBV8 Jim Gibson
Northampton, Northamptonshire, UK   GBR
Lots of good suggestions, if a little tangled up by now. Replacing some of those tired looking components is not a bad idea.

Nobody has questioned the Lumenition module yet. Where is it mounted ?
When I got my V8 in 1978 it had a Lumenition system. The engine occasionally showed the same symptoms that you are seeing,
it would just cut out but could be restarted after being allowed to cool ( that isn't always quick on a V8 ). The Lumenition module was mounted on the LH inner wing, above the exhaust manifold, so I suspected it was getting overheated. I wrote to Lumention asking for comments ( and pointing out that I had didn't know how old the unit was so had no idea if it was still covered by any warranty ). Lumenition simply sent a replacement, but made no comment. I can't now remember how long it was before the second unit started to show the same behaviour, but I replaced it with standard points.

A friend then used the unit successfully on his 500cc sprint car, it was mounted in the air stream. Another friend has a Lumenition on his V8 with the unit mounted on the front of the LH radiator panel, and is very happy with it.
I've no idea whether more recent versions are less susceptible to overheating.

I had determined that the problem was not with the Lumenition optics in the distributor getting dirty, cleaning them didn't give an immediate cure.
( Is the "magnatronic" different ? I hadn't heard of that one ).

Sorry that was a long post for a relatively simple suggestion smiling smiley

B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, MN, USA   USA
1950 Willys Jeep Pickup "Ratrod"
1971 MG MGB
2014 Dodge Charger
Your coil should be getting alternator voltage, plus you have a phasing problem evident by where the spark is jumping from the rotor to the cap terminals. Send those photos to Luminition and see what they have to say. I'd guess you have their Pertronix magnetic kit, not the optical. Plus your rotor is hitting the cap terminals which is a significant issue. Ohm your plug wires as anything more than 5000 Ohms per wire is a major issue. Also, do not run resistor spark plug with resistor wires. Ohm the plugs - they should read zero not 5000 Ohms. You're pushing your coil into failure with the combination of these problems - each of which needs to be addressed.

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Bryan Avatar
Bryan Silver Member bryan strahan
dublin, Ireland   IRL
1968 MG MGC "Ding Dong C"
1973 MG MGB "Ding Dong"
Had a similar problem turned out to be the rotor.

ThomasH84 Avatar
ThomasH84 Thomas Horsley
Woolton, England, UK   GBR
So it was the rotor arm!! It was shorting. One of those suspect black ones with a rivet on the top.

Have replaced with a high quality red rotor arm with the contacts embedded in the plastic and not riveted to the plastic. All running nicely again smileys with beer

Thanks so much guys for all your input. As ever, absolutely great advice to assist with diagnosis. Feel like I've got a much better understanding of the ignition system in the process

Ex-Calif Avatar
Ex-Calif Gold Member Dan D
Cincinnati, OH, USA   USA
1968 MG MGB GT "Bart - Yellow And Naughty"
1977 MG MGB "Red Betty"
2012 Jeep Liberty "Tank"
2014 Hyundai Accent "Skate"
Glad you got it nailed down.

It's really easy to jump to more complicated solutions but Occam's razor usually prevails. The cap and rotor were obviously in need of replacing.

Good job - thumbs up

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