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MG MGB Technical - Push start okay, but not on starter

Hey all,

I've been having a strange starting problem for some time now. If I try and start my B using the starter motor, it will turn over and over but not fire. I get plenty of fuel flow into the cylinders, but she will not fire. But if I give her a push (rolling) start, she will fire up straight away and off we go without any problems. Very occasionally I will get started off the starter motor.

The starter doesn't turn the engine over anywhere as quickly as my Honda, so was wondering if that could be an issue? or could it be the coil not providing enough juice off battery power on start-up? Or even something else?

Anyone have any thoughts on this dilemma? My fiancé is getting sick of pushing!!

Cheers,
Stuart.


Stuart Overell

G'Day Stuart

Could be a number of things

Battery low on power and possibly needs replacing as it can't get up enough voltage and current to turn the starter AND provide enough spark

Ignition coil faulty

Points faulty

Condenser faulty

Plugs stuffed

or a combination of all of these. The slow cranking speed certainly points to a battery problem. Any decent servo will have a battery load tester or Battery World (in NSW, don't know about Vic) will test it for you.

If it has been some time since the points plugs and condenser were replaced, then regardless of the battery condition it is a good place to start. Come to think of it, the plug leads could also contribute to the problem. A low battery with poor ignition components is always going to be a problem.

Cheers

Tony
Tony OIiver

AND another thing, what is your fiances' problem? What better way to keep a relationship alive than to push your MG? I mean, she gets to ride in it when it IS going!

Seriously though, I forgot to say that the starter motor itself may be at fault and drawing excessive current. Any excess current draw will drop the available voltage form the battery and in conjunction with previously mentioned problems will cause the condition you describe.


Cheers

Tony

Tony
Tony OIiver

Thanks Tony for your input.

Updated info:
Battery is brand new - 330cca I think. Plugs are clean and reasonably new as well. The cranking speed seems to sound as fast as the starter will push it - it is not the long slow turnover typical of a flat battery. Leaves me to check points, leeds and coil. The fact that once she is going, she runs very smoothly that makes me wonder whether it more than just a tuning issue.

Stuart.
Stuart Overell

Stuart. The fact the engine starts easily when push started rules out any form of ignition problem. Were it an ignition problem, the car would be difficult to start when pushed, not just when using the starter.

Thus, we are left with the starting circuit. Starter itself may not be capable of turning the engine over properly. Solenoid may not be providing full current flow to the starter. Wire from the battery to the solenoid my be bad, have a bad terminal clamp or a bad connection. Battery ground may be bad--bad connection, cable or attachment to the frame.

Another area which will show up when starting is a bad engine/transmission to body ground. If the ground strap is not attached securely, or if it is deteriorated, you will see it when trying to start.

Put a volt meter on the battery and see what it tells you. Even new ones have been known to go bad. You should see 12.0 to 12.5 volts.

Then, check the voltage at the starter solenoid terminal--the one the large cable from the battery goes to. You should again see the same voltage as at the battery.

Have an assistant crank the engine over while you check the cranking voltage. Should be about 11.5 to 12.5 volts. If lower, you have narrowed the problem down to the cable from the battery to the starter solenoid. If it shows about the unloaded battery voltage, look to the starter as the problem.

Would help to know what year your car is. They used different starters over the years. Les
Les Bengtson

Stuart,

There is one other thing I can come up with.
It might be your ignition key switch. When starting, there should be juice on the white wires as well. Check that. If there is a defect in your ignition key switch, it could be your starter motor is cranking the engine, but without a spark it won't start.

Put a volt meter on the white wire of the coil.
Other end to ground. Crank engine. If no voltage, then probably a defective ingintion switch. (check fuses, too !)

This also is a logical explanation for the fact that the engine will start up right away when pushed. Ignition key in pos. 2 -> white wires get juice. Ignition key in pos. 3 -> actuate starter circuit PLUS juice to white wires.

Good luck.
Very curious to what you will find to be the problem....
Jan

Do you have one of the later B's with the 6 volt coil? If so, then the ignition is powered by one circuit when starting, and another when running. That is, when the key is in the start position, the resistor wire is bypassed. It could be that the bypass circuit has a break in it.
Matt Kulka

I think Matt is on the right track. Perhaps a bad solenoid contact. The coil resistor bypass is to provide higher voltage spark when starting and battery voltage is lowered from the starter current.
Bill Young

First thing to do is see if you have any spark at all when cranking, easiest way to do that is clip on a timing light and watch for flashes - coil lead and each plug lead. If not then use a voltmeter and check for voltage on the coil +ve and -ve while cranking. On both chrome and rubber bumper cars you should have about 10v on the SW or +ve *when cranking* and about half that on the -ve. This should eliminate the ignition switch.

It *could* be not enough power getting to the coil during cranking, although in my experience if there is enough power to turn over the engine there should be enough to generate a spark. I say 'should' because a poor state of tune or other problems that don't noticeably affect normal running could mean that there isn't enough power during cranking. Rubber bumper cars *should* start if the bypass circuit is broken but again if the car is in a poor state of tune or there are other problems it can make the difference between starting and not starting. If the boost circuit has failed you will only see about 5v on the coil +ve and about half that on the -ve while cranking.
Paul Hunt

When I say 'half that' I mean the average as measured on a typical analogue meter. A digital probably won't give a stable reading.
Paul Hunt

Thanks everyone. I will be putting your theories to the test this weekend.

Les and others, my B is a 1967 Mk1.
Stuart Overell

Les is right!
It's the starter dragging!
Safety Fast
Dwight
Dwight McCullough

This thread was discussed between 27/01/2005 and 28/01/2005

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