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MG MGB Technical - Intermittant Starting Issue - 80LE

The 1980 LE had sat for 7 years until this spring when I put time into getting it running again. It's run pretty well all summer, but even during the summer, a few times, it'd refuse to start. I could hear the fuel pump and it sounded normal.

The first couple times, if I let it sit for 5 minutes, it would then start right up.

Recently, however, it wouldn't start after the 5 minute wait and in fact, it would not start for about 2 weeks. I had to move it the other day so I just cranked while in gear to get it to where it had to be. Then, when I went to move it back the same way, it actually started right up!

I'm fairly confident it's a spark issue as I can smell gas out the exhaust.

I did remove and clean all connectors on the stock coil. In the spring I had replaced the ignition relay in an effort to troubleshoot other issues.
Jeff Grant

if you have the original electronic ignition it may be giving you problems. When it won't start, check for spark at the high tension lead from the coil
J Heisenfeldt

Jeff: simple quick check is pull the coil wire from the distr. and hold it near the engine block. Then have somone engage the starter. If you have spark jumping from the coil to the block, then move to the next step. Reattach the coil wire to the distr. and remove one of the spark plug wires and hold it near the engine block. Repeat the starer motor step once again. if there is no spark, the problem is in the distr. Try replacing the rotor with another. I've heard many stories of rotors failing. Another item if you do NOT have electronic ignition set-up, check the points for correct gap and you may want to try a different condensor. After that, let us know what happens.

cheers,

Gary :>{D
79 mgb
gnhansen

Unfortunately, this is a very intermittent issue so it may not come up again this year!

I did replace the plugs and plug wires, but I did not replace the cap or rotor. Does anyone feel this could be the cause of the intermittent starts after sitting a few days?

I'm not sure I understand why it'd typically start a few minutes later. Perhaps the built up carbon was rubbed off during the first attempt.
Jeff Grant

"pull the coil wire from the distr. and hold it near the engine block"

Be careful with this, if you hold it too far away for the spark to jump the gap it will jump through you! Better to pull the king lead out of the coil and hold it an inch or so back, that way you can't get a shock.

With a cranker but non-starter the first step should *always* be to clip a timing light on the coil lead and each coil lead.

If you get no flashes on the coil lead check the voltages on the coil +ve/SW and -ve/CB leads while cranking. They should give different results, and the -ve/CB at least should be varying between 12v and 0v as the points open and close.

If you get flashes on the coil lead but none, only some or irregular on the plug leads then the rotor or cap is breaking down. HT will jump through carbon no problem, it is a conductor after all. The only rubbing on the rotor is from the centre contact there is clearance between the rotor and plug lead contacts.

If all leads flash consistently then any spark problems can only be the plugs. Whilst on 1 and 4 point the light at the crank pulley to check the spark is happening just before TDC.

After cranking a bit take the plugs out. They should smell strongly of fuel if fuel is getting into the cylinders. If they are wet they are flooded, which will happen if you crank too long with the choke out. Close the choke, fully open the throttle and crank to clear the cylinders. Be ready to release the throttle and half-pull the choke if it should fire. If no fuel smell there is none getting into the cylinders, check you have fuel delivery at the carbs, and if so and you have HSs take the lids off the float chambers to check they have fuel in them.
Paul Hunt

Thanks Paul. I'll try your suggestions next time the issue arises.

Keep in mind though, I have an 80 LE with a stock ZS carb. This means it's an auto choke (freshly rebuilt this past spring).
Jeff Grant

Did think about that as I wrote it, could have scrolled back to see if you put the year (which you did although many don't). I'll fall back on 'they are generic diagnostic suggestions' :o)
Paul Hunt

haha, ok thanks.

As I mentioned, I did not change the cap or rotor, so we know they are very (very) old. I don't know how common it is for the coils to fail though, but I did read that it was a bad idea to replace them with non-OE coils due to the lack of added boost in juice during startup.
Jeff Grant

Unless you fit the correct 6v coil you will have to change the ignition wiring as well - it's that that removes the boost during cranking. If you fit a 12v coil and *don't* alter the wiring you end up with weak sparks when running, it's only *during* cranking that you would get the correct voltage to the coil!
Paul Hunt

I know, I did my searching a couple weeks ago. :)

I saw that you had to remove the ballast resistor whenever you install a non-OE style coil. But generally, it was considered a bad idea.

My ignition system is very stock as it sits today.
Jeff Grant

This thread was discussed between 06/10/2008 and 08/10/2008

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