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My 1972 MGB Cranks but won't start

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linklaw John Linkosky
Carnegie, PA, USA   USA
Hello all,

My 1972 MGB with pertronix distributor will crank and crank but will not fire. If I push the car and compression start it, it will start right up. After it is warm, it will start right up. If it sits in the cold overnight or in the garage for a few days, it will not start, unless I compression start it. I cranked it for about 4 minutes the other day and the battery was wearing down, so I pushed it about 15 feet, in reverse, and compression started it on the first bump. Does anyone have any ideas on where to start looking for the problem. I was thinking that the starter may be taking all the juice and not leaving enough umph in the battery to create a spark. Or may have dirty grounds. Any ideas would be appreciated.

John

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Fogliner Avatar
Fogliner Mark Vanherd
Port Clements, British Columbia, Canada   CAN
1974 MG MGB
Are you using full choke?

Mine needs full choke or it won't fire.

After its warm it starts well but cold it always needs full choke.

Regards

Mark

HiPowerShooter Avatar
HiPowerShooter Gold Member James Booker
Lake Winneconne, WI, USA   USA
1973 MG MGB
What does your spark look like while cranking??

IF your starter has enough juice to crank for 4 minutes...there should be plenty to fire it.



"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...

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reinstein Avatar
reinstein RT G
Staples, Ontario, Canada   CAN
1954 MG TF "Alice" ~ For Sale ! ~
2009 Porsche Cayman S
Better try a new set of spark plugs.
Sometimes that's all it takes.
My 72B was a quirky little car also


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LENZ Avatar
LENZ Jim Barlow
Leominster, Massachusetts, USA   USA
1974 MG MGB GT "Murphy"
put on a timing light to see if there is spark. check your timing. check the choke ok?

CMCon98 Colin C
Dedham, Massachusetts, USA   USA
Some cars have a ballast resistor circuit which is bypassed when the key is in the "crank" position. When the key is released, the circuit reverts to routing the current to the points through the resistor. If your B has a similar circuit, there could be a fault that's preventing you from getting enough juice to the points while cranking with the starter. (Some cars energize a relay when the key is turned to 'start', which routes current around the resistor) Once the engine is good and warm, it spins easier and faster on the starter, and it may have enough inertia after you release the key to fire a plug and start. Could also be intermittent problem with the ignition switch.

Wachtmans Avatar
Wachtmans Wouter Strodijk
OVERVEEN, Noord Holland, Netherlands   NLD
1974 MG MGB "The Bee"
1974 MG MGB "The Bee"
1974 MG MGB MkIII "The Bee"
I bet, it's the battery terminals that need cleaning.

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barry s Avatar
barry s Silver Member Barry Stoll
Alexandria, VA, USA   USA
1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
There is no ballast resistor on an OE '72.

If there is a potential for "dirty grounds", clean them. Poor grounding is a source of many recurring problems and deserve attention.

As stated, full choke should be used when starting. Also, see that the choke linkage moves when the choke is pulled.

RAY 67 TOURER Avatar
RAY 67 TOURER Ray Marloff
Fort Bragg, CA, USA   USA
1967 MG MGB "My Girl"
If the engine starts with a bump start, the problem is most likely in the ignition switch or starting circuit. With the key in the ON position, and not the START position, current is going to your coil and the engine is allowed to start right up. RAY

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linklaw John Linkosky
Carnegie, PA, USA   USA
Thanks all for the tips. I will have a chance to mess with the car again this weekend. I will let you all know what I find out.

John

CMCon98 Colin C
Dedham, Massachusetts, USA   USA
Also, if your battery voltage at the starter is low, or your starter is worn and cranks slowly, it would cause these symptoms.

J Baz Avatar
J Baz Silver Member Jerard Basmagy
Middletown, New Jersey, USA   USA
I once had a car that had no spark on crank and I had to quickly move the key back one click to get it to run when cranking. Turned out to be a bad ignition switch.



jb

Too soon we get old, too late we get smart!

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