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MG Midget and Sprite Technical - Had intermittent ignition problem 1500 IT'S BACK

Son-of-a-gun.....
I had that 'quitting when hot' problem some time ago. I replaced the ignition coil and thought I had it beat.
This morning, I did some highway driving, some idling at the post office and sure enough, that got everything hot enough that the engine died. It started up within seconds, but quit again right away. Then it was a 1 1/5 mile push to my folks house, sweat, sweat, pant....Good thing these cars are small and traffic was light.
After sitting at my folks for some time, it started and got me the 8 miles home.
Trying to figure out what to look at now.
1500 with electronic ignition, new coil....From what I see, the ballast resistor should be 1.3 to 1.5 ohms. When that cools (boy it was hot), I'll read it.
Open to anything. Thanks for reading.
Paul
Paul W 1976 1500

Have you tried replacing the rotor arm with a red one?

Peter
Peter Burgess Tuning

Have you considered fuel vaporisation in the feed line to the carbs? 1500s are prone to this.
Guy W

Sure I suggested a faulty ignition/starter switch last time.


Well that's what mine was with similar symptoms.



Regards Steve
SR Smith 1

Guy said:

Have you considered fuel vaporisation in the feed line to the carbs? 1500s are prone to this.

I didn't know that. Thanks Guy.

Internet suggests it's warm in Buffalo right now. High 20s to low 30s (Celsius). Maybe 85 to 95 Fahrenheit. Does that sound right?

So it's a possible. I've never had a vapour lock problem in my 1500s fuel line, but it's never seen anbient temperatures in that range. And as you say it quit while idling which is exactly the time you'd expect to see vapour lock if it was going to happen. Low airflow, low fuel flow etc.

Peter said:

Have you tried replacing the rotor arm with a red one?

x2 Peter. For all it costs, that's got to worth a try.

FWIW I don't think the ballast should be getting seriously hot. Warm, yes; but not roasting. But if it does it should reduce the resistance and result in higher voltage at the coil primary, not lower.

The thing that got my attention was that it restarted when hot then died right away. I kinda feel that's pointing towards a fuel problem when hot.

Hmm....interesting. I hope it's nothing more serious.
Greybeard

Definitely another vote for a fuel problem due to heat, as suggested earlier.

Make sure the heat shield is intact, for starters.
JB Anderson

Check all the fuel lines for collapsing....replace them all. Ive seen ths problem before
Steven Devine

Also check to see if your gas tank gets pressurized. release the gas cap and listen to see if you hear depressurization.

Ha ha is depressurization a word? Ha ha ha
Steven Devine

Steven and JB........
Good catches.
Depressurisation (or tank vacuum).
I didn't think of that. Easy to check. You need a temporary Prop-spec tank cap. A spray can top with a hole in it so you can eliminate a breather problem.
Good point on the collapsing fuel hose Steven. I just today found this on a Ford diesel.
Greybeard

With a fuel problem, vaporization or otherwise, wouldn't there be sputtering, or something similar ? This just shuts down like you clipped an ignition wire. It didn't quit when idling, it quits at cruising speed.
No, I haven't swapped out the rotor arm. Who has the red ones ? Does Moss ?
Yes, it is warm here.
Thanks guys....
Paul
Paul W 1976 1500

Red rotor from Distributor Doctor. Don't know if Moss has them.

Sorry Paul, I misunderstood the original post and thought it quit at idle.

(Steve the prob is not the tank pressurising. It's more of a vacuum problem if the tank can't breathe. The telltale "whoosh" when you take the cap off is sucking, not blowing air).

Vapourisation could still stop the engine at cruising speed after a period of idling. The vapour in the fuel line wouldn't be a problem until the float bowls emptied and tried to draw vapour instead of liquid fuel. If you see what I mean.
Greybeard

Greybeard,
you are right I meant vaccuum...good catch!

I dont believe in vapor lock! Ive worked on a lot of different antique cars and I have never seen it.

I was working on a spitfire 2 years ago and went threw the whole deal with this same issue for a customer.

We added heat shields changed ignition parts etc etc....In the end I found an old fuel line from the tank to the inlet line. It looked fine on the out side but would shut off the fuel intermitantly killing the engine. It shut down just like you turned it off.

One of the most frustrating problems to find we had about 24 hours of non billable time...but I did get it!

It may not be the answer but if you change your hoses at least you can rule that out. Its cheap and effective.

:-)

Goodluck and I hope you find your problem and post the solution!
Steven Devine

Thanks guys.
I just bought this deal on ebay.

http://www.ebay.com/itm/181807169268

Red rotor, new cap and new wires.

I'll get a look at the fuel lines too. If I drove with the gas cap half-locked, would that eliminate the possibility of a vapor lock ?
Paul
Paul W 1976 1500

"I'll get a look at the fuel lines too. If I drove with the gas cap half-locked, would that eliminate the possibility of a vapor lock ?"

Nope. It might help to identify a tank breathing problem, but the most likely thing you'll learn is the cost of a new tank cap!

As Steven suggested earlier, if you take the tank cap off immediately after a run, do you hear a "whoosh" noise as the tank sucks air? If so there is likely to be a fault with the cap breather. They do block up now and then. I had to buy a new cap for my wife's POS Ford last year because I couldn't get the breather to clear. Bad breather can stop an engine but it's more likely to stutter and lose power first rather than just cut out.

As Steven says a collapsing hose can do it too. I just replaced one on a diesel engine in a boat yesterday for that very reason. It will only cost pennies to replace the hose and it might fix the problem.

Vapour lock happens for real. I didn't know 1500s were prone until Guy mentioned it but I drove a Toyota pickup around when I worked in Abu Dhabi which liked to take a little break now and then. Eventually solved with a huge heat shield and insulating sleeving on the fuel lines.
Greybeard

This thread was discussed between 03/09/2015 and 04/09/2015

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