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MG TD TF 1500 - Pertronix Rough Running issue

I have a pertronix LU 146 negative ground symetric unit, The coil is putting out 3.7 ohms. A new distributor cap with a Moss red Premium rotor. With the standard points it ran fine, I switched to the Pertronix and if ran very rough and would not hold an idle and died. I then put the original back in and it ran fine again. Once more I check wiring and every step and same very rough running. Then I finally put the original back in and ran fine. Need to know if there are failures with these units. I have a 1954 MG TF 1250 engine and was told by Moss this is what I needed. I have seen some dated discussion as sometimes the rotor sets too high for your ring.

Does everyone agree that the symetric/high lift is the correct for TF? I had a head replaced on the car and they used the earlier banana hole head which takes the shorter reach 1/2 inch plugs. Am I correct that if nothing else on the engine was touched, it should not affect the distributor?
K E MURPHY

If it is one of the newer units,
Bud Krueger figured out years ago that they won't work with original solid core wires. You have to change to modern resistor wires. Search the archives. The old style had the problem with the slip on collar jacking the rotor up. The cap wouldn't fit down all the way, and/or jammed the rotor into the center contact/cap. George
George Butz III

An LU-146 would be an original type of Pertronix that uses the magnet ring, So, OEM ignition wires should be fine. My first question is, "did you set the timing after installing the Pertronix?" I can't imagine your using a symmetric collar with a TF distributor. High lift would be what I would expect. Is the collar a snug fit onto your distributor cam? You can set/check the timing of a Pertronix system with a lamp, just the same as you set it with a points set. Just remember to disconnect the lamp before firing up the engine.
The problem that George mentions is shown in http://www.ttalk.info/Failure.htm. It's caused by an accumulation of carbon in the distributor cap. Bud
Bud Krueger

Bud, Do the new ones have an 'LS' suffix? and do they have the slip on collar which causes the space issue? George
George Butz III

Keith, I would put a timing light on it and check the timing with the Pertronix first. Next check with the light for fire on each cylinder and see if you find a dead cylinder which would indicate a possible defective collar ring (as in a bad or missing magnet). Also check the voltage of the battery when running. The Pertronix requires a full 12 volts to function properly. Your points do not.

Just a couple of things to look for.
L E D LaVerne

I recently installed a 123 ignition. I had a consistent misfire at low revs and bad idle. I chased it for a while until I did a "think". The distributor is badly grounded. I put a ground wire from the bolt that secures the clamp to the distributor body ( not the bolt that screws into the block ) to the frame. The problem went away.
Charlie
c mac quarrie

George Butz, and everyone else Thanks I will add that I am using Bumble Bee stranded core plug wires from Moss. Should these work on the Pertronix? The Pertronix runs but just so rough and no idle, it dies. Also I have ruled out having one bad plug/wire as they all run fine when hooked to my normal points setup.

I am assuming this is a new unit as I actually just received from LBC. On Moss site it says "early TFs had a symetric cam. The later TFs (1500?) had a High Lift cam." Now the interesting part is that the Petronix part number is same for both Symetric and high lift 222-573.The TD is the one that has an Asymetric cam.

Friends LaVerne and Bud and anyone else - Do you think it could be the rotor - the new red one Moss? The ring and rotor both press down into place it seems.

I have not timed the engine - still works fine with points - but sound like it might be neccessary according to some of you. The person at Pertronics says it shouldn't need re-timing. But kind of "seems" to my less than expert simple mind that might be the issue.

It has been 30 years since I have timed and I forget how!! Seems that I need some kind of timing light? Something I can do myself? Maybe I will have to look at archives. I remember vaguely looking at the front of engine for markings and TDC and such mysterious letters. I know at 75 and driving it 40,000 miles I should know this stuff. Newfoundland, Indy, FL Keys - It only let me down once!! And that required the only spare I carried with me - a fuel pump, changed at a Holiday Inn in a shady part of Miami!
K E MURPHY

George, the newer ones with the LS suffix are 'Lobe Sensing'. That's the LS. They do not need the magnet collar. The sense the function of the distributor lobes. They are computer-controlled, rather than just Hall-effect devices. They sense the differential of the magnetic effect of the lobes on a magnet. That's why they are sensitive to EMI from hard-wire plug cables.

K.E. Is your magnet collar a snug fit on your distributor cam? Does it drop down all of the way when you put it on? Do you have a spare points plate onto which you have mounted the Pertronix? That sure makes a swap easy to do. It's been my experience that by far most Pertronix failures have been the result of something to do with the installation. But, like any other electronic gadget they are prone to have defects. There are probably at least half a dozen of threads in the archives showing how to set/check timing of our cars. Check the archives. Are these Bumble Bees a hard wire, i.e., metallic? Bud
Bud Krueger

Bud, I did know about the new one without collar, maybe I should check it out? Yes the rotor and ring seem to fit correctly and snap right down. I can easily swpa back and forth as the Petronix comes with the gizmo mounted right on the plate they provided. My Bumble Bee wires have traditional copper strands of wire. The Bumbles seem to be thicker insulated. Will look for archives on timing. Thanks so much!
K E MURPHY

Pretty sure you have to re-time it. Easy to check- mark where the dizzy is now, then loosen and rotate it back and forth and see what happens. I think there are details in the archives somewhere. George
George Butz III

This thread was discussed on 21/06/2020

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.