Electrical Problem

[scott_74]

Hi all. I apologize in advance for being long-winded, but I'd rather give too much information than not enough. I am very much a novice so forgive me.

I have a '74 1275 MG Midget with twin SU carbs. In the beginning of the year, I took it into the local British car shop because one of the carburetor butterfly discs had broken apart (this was a brand new carb installed 2 years prior). The car wasn't running right so I feared one of the bits went into the engine. The shop didn't find anything, but they ended up doing a whole bunch of much needed servicing. This included performing a valve job, surfacing the head, installing a new water pump, replacing the points and condenser, readjusting the carbs, and replacing most of the hoses. They also removed the smog equipment.

They tuned it all up and the car ran great for not even a few days. One morning on my way to work it started to backfire out the exhaust pretty bad. And the following day it wouldn't even start. I ended up getting the starter rebuilt. I was then able to start it, and although it ran great initially for a bop around the block; soon thereafter it started to have problems. I could barely get it to start, and when it did start, it ran extremely rough. Though it didn't backfire anymore, it ran very rough...like it was constantly having then losing power.

I ended up towing it back to the shop. They did a number of tests, and ultimately let me know that the new condenser had gone bad. They replaced it, I picked it up, and it ran great for 24-48 hours with some heavy driving. Then, intermittently, the car would go through surges of loss of power. In some cases, it would stall the car. But it would be running great between these episodes. Although it was intermittent, it seemed to be at it's worse when the car was just started and warming up.

The problem got worse and to the point where I could start up the car, it'd run rough for a few seconds, then it'd die down. I ended up buying and installing a new coil with no resolve.

The problem has got to be electrical. The timing has been checked and the carbs adjusted. And the carbs are definitely getting fuel. I don't see any loose electrical connections or split wires. Unfortunately, I don't have any tools to test the various parts of the electrical system. Could a bad coil have caused the condenser to gradually die off? Is it worth trying a new condenser again? Pending any great ideas from you folks, I'm planning on taking it back into the shop.

Any ideas?

Thanks!

Scott

 

[Trevor Jessie]

Condensers are cheap... stick another one in and a new rotor button just to be sure.

 

[RickB]

If you still have your original condenser put it in.
The new ones have been notoriously bad.

I went though a lot of the same symptoms with an MGB I recently sold.
My problem ended up being a small deposit (visible with a magnifying glass) on the surface of one side of the points contact. Just enough to make everything horrible.

A points file to the points and resetting the gap and I was back in business.

As Trev said - rotors have also come under suspicion lately.

 

[spritenut]

If the points, condenser, and rotor swap do not make any difference, I think maybe the distributor weights are hanging up causing the timing to be good, then bad when the weights advance and stay advanced.
To check the guts of the distributor, remove the cap and twist the rotor arm gently counter clockwise, is should be loose and move about a 1/4 inch and snap back when you let go of it.
Gunk over the years gums up the weights.
If they are not advancing, it will start but run like crap when you step on the gas.
Also, do you still have the gulp valve on the car?
If so, try removing it and plugging the hose with something (a spark plug fits this hose perfect as I have seen my share of spark plugs plugging gulp valve hoses. My current 69 project has a spark plug in the hose.

 

[RickB]

Ha Frank, I've put my share of spark plugs in those... :wink:

 

[scott_74]

Thanks guys. I'll try what you mentioned and let you know.

Scott

 

[jvandyke]

Your battery is good and the charging system working? I guess you'd know that pretty quick as it wouldn't last too long, unless you keep it on a tender and masked the problem? Don't know, just guessing.

 

[scott_74]

Yup. I replaced the battery as well. Charge doesn't seem to be the issue.

 

[JPSmit]

the other question I have is whether air is getting in somewhere, around the carbs or the manifold? if you can get it running, spray around the joints with WD40 and if the idle changes that might be it

 

[scott_74]

I had tried that too when I thought it might be fuel/air related. There was no change in the idle.

 

[regularman]

If those points were put in with the new condenser, then they might have worn in and closed up and you almost have no gap. Always recheck point gap after a few hundred miles.

 

[Sarastro]

If you really have had a bad capacitor (or condensor, if you will), it's likely that the points are burned. So, cleaning them up with an ignition file and readjusting them might be in order.

Are you sure the capacitor-to-points connection is installed right? There some shoulder washers as insulators where the wire from the cap connects to the points, and people get this wrong all the time. Result is shorted points (which you don't have, or the car wouldn't run at all) or, more likely, a disconnected capacitor.

No, I can't see any way a coil problem could blow the capacitor. About the only thing that can go wrong with a capacitor is a short or open circuit. Short circuit will kill the engine immediately, but an open circuit, especially an intermittent one, will fry the points quickly. A short-circuited cap is easy to find with an ohmmeter; an open one not so easy, but the effect on the point is clear. If you don't see either of these problems, the cap is probably OK. In my opinion, capacitors are blamed a lot for things that are not their fault.

Rotors get blamed a lot, too. A rotor is just a piece of plastic with a metal strip. About the only thing that can go wrong is a crack in the plastic.

I've seen distributor caps that simply are not made to the right dimensions, so the cap doesn't fit right and the gap between the rotor and the high-voltage contacts is too great. I suspect this is a major reason for "bad rotors." Some rotors also might not be made to quite the right dimensions. I haven't seen this, but so many other replacement parts are crap, no surprise if they are too. Suspect everything! Paranoia is sanity!

Don't rule out a fuel problem, just because the carbs are getting fuel. The float valve could be sticking slightly open, for example, and the fuel level getting too high. This is pretty common after a carb rebuild. It's also consistent with the car running OK when first started then quickly going south.

In short, this really could be one of many things. It shows why it's a good idea for everyone who has one of these cars to collect the tools and literature--primarily a shop manual--necessary to do at least basic work.

 

[jlaird]

If the small wire in the dizzy that goes from the coil to the dizy case to the points gets grounded, poor insluation after 40 years you will get an intermitment miss, etc.

Some time ask me how I know. Man is that hard to find.

 

[Glen_B]

Jack,

The coil can also cause the described problem. Swap in another without any other changes and see what happens.

Glen Byrns

 

[jlaird]

Oh yea, of course. Finding the grounded wire was after I replaced everything else of course, lol.

 

[walshja]

Scott, the guy I purchased my 1974 from told me a story about another 1974 he had.

He removed the smog equipment and experienced the same problems you are experiencing.

He tried everything trying to get the car to run properly and never could, so he put the smog equipment back on and everything was fine.

just thought I would throw that out there

 

[scott_74]

Thanks for all the replies.

I swapped in a new condenser (without removing/disrupting the rest of the distributor) and it fixed the problem. At least for the moment. I find it hard to believe that both of the previous condensers were just "bad eggs." I guess I'll find out soon. It took the last one 1 or 2 days before the car started to act up.

I assume the points are in good shape since it runs great at the moment. So that rules out an open-circuited cap, correct? Is there anything else that would cause a condenser to go bad that I can check for? I just have a bad feeling that I'll be back to the same problem in a couple days.

 

[Sarastro]

I'll bet dollars to donuts that the capacitors were OK but you fixed an incorrectly made connection, or perhaps moved the connection wire so it's not in danger of shorting, as Jack suggested.

Speaking as an electrical engineer with 40 years of dealing with broken electronics, I can say unequivocally that it's extremely rare for ordinary capacitors to fail. (Electrolytics are a different story, but the capacitor in your distributor isn't one of those.) The only failure mode I can see is a badly made connection of the wire to the interior foil of the capacitor, which could short circuit or come loose. Given that most of the replacement parts for these cars are pretty crappy, that's not at all impossible. If that's what happened, there is probably some degree of burning of the points, but if the car is running OK, probably best to leave well enough alone.

Glad to hear that you got it going though. Have fun with the car!

 

[RonMacPherson]

I ran the diagnostic center at Joe Vittone's Auto Center(The VW, Honda, Datsun dealer) in Riverside in 1973. We ran into a whole bunch(I mean at least 60) of Delco condensors that were used in the Fiat 124's that were basta....

Our techs would do a tuneup, a week or so later(seemed to be dependent on mileage driven) the car would come in on the hook and come to me for diagnosis.....

So they can be badly made...... Experience shows that..

And that is just one repair facility's experience. Dunno how many others from the same batch were basta. And these were factory pipeline parts.....

 

[Sarastro]

Actually, getting a batch of parts (any kind of parts) that's bad at the outset isn't all that unusual. Having a properly made capacitor fail, after it's been working normally for some time, is what's unusual.

When you see something like this happen, check the batch numbers and return the whole batch to the mfr. Be sure to include a really indignant note.

This whole capacitor issue is intriguing. If anyone has a capacitor they are sure has failed, send it to me (Steve Maas, PO Box 7284, Long Beach, CA 90807) and I'll do a post mortem and report what I find. (Don't send it until June, though, since I'm in Sweden until then...!)