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MG TD TF 1500 - High speed miss...

For a very long time now, I've had a high speed miss with my TF-1500. It was always a minor nuisance until this past weekend during a short trip to a car show when it became almost constant. Before it was always intermittent and almost not noticeable except to me. I suspect that it is a distributor problem but certainly could be wrong about that. The car does have a fairly new pertronix ignitor in it. Thinking that perhaps I wasn't getting a good zap to the plugs, yesterday, I cleaned the inside of the distributor cap where the plug wires go in and cleaned the little brass connectors and re-flayed the pugs wires but during that process, I noticed that one of the lugs on the inside of the distributor cap had a nice little grove chewed out of it. That indicates to me that the rotor is not turning in a true circle as the opposing lug shows no wear (numbers one and four). After I completed yesterdays attempt to fixing this problem, I took it for a test drive and it did seem to make a difference but only for a short time. I've attempted to attach a picture here to see if anyone might have a solution for me to try next. I don't know if you can make it out very well but its the lug at the top of the pic.

Thanks in Advance - Dennis


D L Rainey

Dennis -- I had a similiar problem a couple years ago and lived with it till the car stopped. Found out that it was the rotor. It looked OK but the car won't run with it. Checked the rotor with my electronic instruments and could find no problem. I have labeled that rotor very carefully and keep it to show people who don't believe.

About your distributor cap I would take it to a machinist and have him check it for concentricity. If he says its OK then send your distributor to Jeff (whats his name) that runs a dist. rebuilding service. The bushings in the dist. must be bad.

My 2 cents worth.

Cheers,

Bob
R. K. (Bob) Jeffers

I had the same problem when I installed a Pertronix on my car. It kept getting worse. I did some searches and learned that the aftermarket rotors where the metal is riveted to the plastic have this problem. Eventually the rivet arcs internally to the metal clip and the shaft. Get rid of it.

You have two choices. Find a genuine lucas rotor that doesn't have the rivet, or order a proper reproduction from Kip Motor company.

http://www.antiquedistributorcaps.com/

His web page describes the problems. The pertronix seems to make the problem worse, because it works better than points, and you have a stronger spark due to their longer dwell at high speeds.

The problem went away, and I have a lot more power than it ever did with points. An MGB was tested with points and pertronix (dyno) and it gained 5hp with the pertronix. It is well worth the price, just for this.

I couldn't find my used lucas rotors, and got the one from Kip. Then I found the lucas ones, and compared them, and they are identical. The brass is embedded in the plastic, instead of riveted on with metal.

regards,
Larry
Larry Ayres

Jeff Schlemmer is the name you are looking for Bob. Jeff did my distributor this past winter and what a difference it made. His business is Advanced Distributors and the web site is: http://www.advanceddistributors.com/ Jeff's work is terrific, his prices reasonable and the turn around time is very quick. Cheers - Dave
David DuBois

Dennis, if the rotor is contacting one of the poles in your distributor cap it indicates that your central shaft is not concentric with the cap. It is likely that the top part of your distributor is loose on the bottom part. Try taking the cap off and grasping the cup part of the distributor and try and rock it. If there is any movement at all you will need to fix it.
Regards, Richard.
R Payne

Thanks all for your excellent support. I forgot to mention in my first post that the problem seems to appear around 3000 rpms if that should make any difference. Presently leaning toward sending the distributor off to Jeff Schlemmer so that he can work his magic.

Cheers - Dennis
D L Rainey

Now there is no reason to doubt that in your case the problem is with the distributor cap, but for the record I've once had a similar problem and it was due to burnt-out points, which got short-circuited, acquired that typical bluish tinge and lost elasticity. Car would not run above 3,000 rpm's - not good to me, being a bad guy I like over 5,000!
Denis L. Baggi

This thread was discussed between 19/05/2008 and 21/05/2008

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