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MG TD TF 1500 - Bad Miss

Here's hoping someone can help. I have a '55 TF-1500 with a rebuilt engine with approx. 1000 miles on the rebuild. After about 20 mins. of driving, it begins to miss as you are putting a load on it ie., going thru the gears from a stop sign. When you reach cruise speed, it tends to smooth out. The longer that it is driven, the worst it seems to become. My first thought was a fuel delivery problem. I tried everything that I could come up with, checked the fuel filter, cleaned the float bowls, took a gas sample from the bottom of the tank looking for fuel contamination, etc., all to no avail. Haven't really gotten into the electrical side except to see that everything is in place and proper.

Any ideas out there?

TIA Cheers - Dennis - Sacramento
Dennis Rainey

Dennis,
What condition is your coil in? If its got some age on it I'd suggest trying another and seeing if that cures the problem. I know from recent personal experience with the hot weather we've had here this summer!!
Mark
mark

Hi Mark,

The coil thats on there was put on by the PO. Hadn't even considered the coil. Will give it a try and see what happens. Thanks for the suggestion.

Cheers - Dennis
Dennis Rainey

Hi Dennis;

I had a similar problem with my 52 TD about two years after rebuild. It turned out to be the condenser in the distributor which was at least thirty years old and breaking down. I didn't even think about changing it after the car rebuild was complete and initial engine runs were done. I guess that Lucas parts only last so long!

Good luck
Dick
Dick McCutcheon

Dennis,

Try to isolate the problem first as to if it is fuel or ignition. If you only experience the problem when driving the car, i.e. under a load, this is telling you that it is probably fuel related. If the car will "miss" at rest when reving the engine and while driving, then it is probably the ignition system. Ignition faults are not load dependent, where a fuel problem often is. Make sure your condensor is in good shape and check that the tach box is not shorting out the low tension terminal on the side of the distributor, two common suspects.

Good luck, Ben T.
Ben Travato

Dennis,

The identical thing happened to me (55 TF 1500). I thought it was a fuel problem, too, e.g., leaking throttle shaft bushings where it got worse as the temperature rose, but at higher RPMs, where a small vacuum leak wouldn't matter so much, the missing was not as bad. Sent the carbs to Joe Curto who did a wonderful job - they're like new, now. But, put them on and the same thing happened (so much for self diagnosis). So, it had to be ignition. Traced all voltages from the battery through the ignition switch, ameter, coil, across the points. Everything was fine. So now I was convinced it was an intermittent coil problem, 'cause as soon as it heated up, there was intermittent or no spark. But I coudn't "catch" it with the volt meter (so much for self-diagnosis, again).

So, the only thing left was that the points were not gapped properly. Sure enough, when I cranked the motor over by hand, I could see the points were barely opening. Apparently, before everything heated up, the tiny gap was enough, but as it got hot, the points would not even open. So, I gapped the points and the car started up with a quick pull, and has run absolutely flawlessly since (except I found I had to REALLY crank down on the screws that hold the points to the distributor plate or they just crept closed again). It was so simple all along, and I hope this helps.

Greg
Greg Van Hook

Check the dist. cap wire/nuts. I have had the coil wire come loose/burn off in the middle of the cap twice- most recently a couple weeks ago.
George Butz

Dennis,
Have you done any distributor lubrication?
Sounds like the advance mechanism could be "dry". i.e:
Light "smear" of engine oil on dizzy cam...couple of drops down the cam spindle and to the side of the cam for the advance mechanism. Very cheap fix if it works!
Worth a shot?
Regards,
David 55 TF1500
David Sheward

Ladies & Gentleman, Boys & Girls, Friends and Neighbors and relatives and most of all to those who frequent this BBS,

Over the weekend, I managed to isolate the problem that was plaguing me and fix it. The problem was correctly diagnosed, by Greg, as needing a points ajustment. The hold down screws on the breaker plate had come loose and hence the points had slipped out of adjustment. During all of this, I discovered something worth a mention. The inside area of the coil where the coil wire plugs into, was very corroded. This had to have restricted current flow to some degree. My question is, if this isn't corrected or checked from time to time, will it become a serious problem if left unattained. Has anyone ever had an experience with this problem. I've not read anything on this BBS or for that matter any place else on this subject.

Anyway, Thanks to all. Couldn't have done it without ya.

Cheers - Dennis - Sacramento
Dennis Rainey

Dennis (and other contributors), Glad the problem is now fixed. Another cause could have been, but clearly not in this case, that the fuel pump was not working as efficiently as it might, and not delivering enough to the carbs when on load. This would affect the front carb, since the rear one will always have enough because of the layout of fuel lines. I replaced my pump (TF early low pressure type) recently - I got fed up with tapping the old one with a screwdriver handle to persuade the it to function. This has made the car run more smoothly. I have now seen adverts for the electronic pumps, which look like the original - I kind of wish I had bought one of those.....AB
Adrian Bennett

Adrian,
Wouldn't you miss the "ole tickity-tickity" conformation that the pump is operating? I guess one could record this and install an audio system for playback! ;-)!
Cheers,
David 55 TF1500
David Sheward

David, True, true - in my case, before the swop out, it was more "t i c k i t y - t i c k i t y" - ideal cure for insomnia... AB
Adrian Bennett

For the record, the "new" electronic SU pumps supposedly do still emit an authentic ticking sound and are made to look exactly the same as old originals.

Transistorised innards replace the contact-breaker mechanism; you can also buy retrofit kits to transistorise your existing pump.
Will

To Adrian, David and Will:

No, I have not installed an audio system to listen to my two SU pumps, but I have two LEDs that glow every time a pump clicks. I did that by putting two large diodes in series with each pump with a LED across. There is a more elegant solution by Carl Cederstrand who simply connected a 12-V bulb to the "other" pump terminal, just symmetrical of the contact - but you have to drill the cover to get that.

Denis
Denis L. Baggi

This thread was discussed between 19/07/2002 and 10/08/2002

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