View Full Version : Coil Question

07-29-2005, 10:56 PM
After discovering last weekend that the new rotor button, which I've been driving on for about 600 miles was too short by about 3/8" and having received and installed a new proper one, I'm thinking I need to replace the Lucas sports coil as well. The reasoning is: the coil could no longer jump the gap last weekend, which is why the car suddenly died on me. With the right button it now runs, but after taking the car out for a short test run last night, the darn thing backfired when I shut the key off. My brother, who is much smarter than I am about things electrical, says my coil was cooked, or rather half-baked, not completely ruined, but enough to change the fields, causing the car to backfire (?).
I was hoping to get a coil from the local auto parts store tonight. Obviously, they had no Lucas on hand, but they had plenty of others. The kid behind the counter, though helpful, couldn't tell me if I needed an external resistance or internal resistance coil and I didn't want to chance of frying something else by installing the wrong thing. And I thought coils were coils...
Is there a coil out here that I could get my hands on tomorrow morning that would be a proper fit (I am also running a Crane EI) until I can re-order a new Sports coil? It's our anniversary tomorrow and my wife and I were looking forward to taking the car to the coast and dining on sea roach (lobsters to you land-lubbers!)

Dave Russell
07-29-2005, 11:23 PM
Hi Dave,
Is that the only thing wrong - That it backfired when turning it off? If so, it is characteristic of "some" electronic ignitions to create a random spark when they are switched off or on.

Though possible, it would be unusual for a coil to partially fail. If the car runs ok otherwise, I wouldn't worry too much about it.

07-29-2005, 11:45 PM
Listen to the man with the Healy. if it runs fine otherwise, I'd say its not the coil. When they go they tend to shut off when warm, rather than causing a backfire. That sounds more like a slight timing issue, or an electronic ignition issue.

07-30-2005, 11:32 AM
I agree it's not likely the coil. If it's putting out enough to jump "normal" gaps between the rotor and cap and those on the plugs, you should be OK.

In the future, you can determine which type of coil you need by looking at the wiring and digging out your volt/ohm meter. Since the coil is still working you can make this measurement now. Mark and remove the low tension wires from the coil. Measure the ohms across these bare coil terminals. A "standard" coil will measure "about" 3 ohms. A coil for ballasted ignition will measure somewhere between 1 to 2 ohms. When you reconnect the wiring on a ballasted ignition system you should find at least one power wire going over to the starter solenoid. On some cars with ballasted ignitions there is no "visible" external resistor. The supply wire from the ignition switch is a resistor wire (and may be "pink" in color).

If you're running the Crane/Alison ignition they probably have some specific recommendations on the coil ratings you should follow once you know whether you've got a ballasted ignition or not.

07-30-2005, 11:37 AM
A better place to look for a cause of backfire is a worn advance mech in the dist. I have seen a coil quit from a broken rotor but that was that, it quit and was stone dead.(darned ol Bosch piece of german junk!!)
MD(mad dog)

Geo Hahn
07-30-2005, 01:47 PM
In the future, you can determine which type of coil you need by looking at the wiring and digging out your volt/ohm meter. Since the coil is still working you can make this measurement now...

[/ QUOTE ]

Of course that assumes that your current coil & wiring is correct. I think you will find that the Lucas Sport Coil does not require an external ballast and that that is correct for a 250.

I also agree that the 'coils failures I have known' have been sudden occurences without warning or prior symptoms.

07-31-2005, 10:12 AM
I want to thank everyone for their help in this and in other areas I've had questions about since I re-installed the motor a couple of months back. I must say though what was supposed to be an exciting and longed-for improvement, it's been a huge headache to sort through these performance issues. I have yet to be able to take the car out for a long ride without worrying that it was going to leave me and the missus' stranded somewhere.
Yesterday morning, after reading the posts above and searching through three years of previous posts on this subject, I removed the electronic ignition from the car. My brother came over and we worked on the timing and carb adjustments for nearly 2-1/2 hours until we had it idling smoothly for the first time since the engine went in. Needless to say I was feeling pretty good. After he left, I took the car out for a test ride of about 8 miles that included a short stretch of interstate where I got the car up to 70-75 and it didn't miss a beat. Got home and told the wife to get ready for the trip we had planned. Of course, she was somewhat hesitant to take the Triumph, but I assured her everything seemed fine. An hour later, we're on our way and a mile into the trip the car starts to buck and skip, then run fine for a few hundred yards and then buck and skip again. Needless to say, we turned around and went home. /ubbthreads/images/graemlins/cryin.gif
I'm beginning to think that most of my problems are now carb (dual Weber 32/36 DGV's) related, not that I didn't have timing and ignition issues as well but those I believe have been corrected. I am thinking of removing the carbs from the car today and install some new jets I received last week, check the floats and just do an inspection. The carbs sat on a shelf in my cellar wrapped in a garbage bag all of last winter while the motor was being re-built. Maybe they need a thorough cleaning. The fuel filter is brand new, having replaced it when I installed the motor in June. I don't know what more I can do.
The adjustments on the carb are extremely touchy-just moving the idle screw for instance a fraction of a turn will cause the engine to rev much higher, or nearly stall, depending on the direction of the turn. After getting the idle right in the morning, it wouldn't idle below 1500 rpm in the afternoon; kick down on the accelerator and it still wouldn't drop. Wait for a few minutes and it would slowly come down on it's own. There was that intermittent skipping that I experienced yesterday. I have checked for vacuum leaks by spraying (carefully spraying) starter fluid around the carbs and intake manifold. No change in engine speed. That's about it for symptoms.
Would undersized jets be the cause of these problems? Incorrect float adjustment? Inadequate fuel from the mechanical pump? All of the above?

07-31-2005, 01:46 PM
Dave, out of curiosity, what possesed you to go with the Weber carbs. In my minds eye, some of the inherent value of the 250 is modified with such a drastic carb change. The Weber DGV's are not that well suited to the Triumph 6. I have had two TR6's with this setup and applauded the day I changed them back to ZS carbs. The Webers are not that adjustable, save changing jets and tubes, and are not performance oriented. Obviously some on this forum will argue loudly against this observation, but I feel that going back to dual Strombergs (bet yet, triples!) would give you much more instant tuneability and driveability. Also, watch the fuel flow on these carbs, you may have to choke down the line to about 1.5 or less. Getting someone like Joe Curto or Gary Martin to overhaul to concours condition some ZS carbs might put you back in the purr of things. I could give my eye tooth for a TR250. These are the ultimate Big Triumph (save a LHD TR5).


07-31-2005, 02:13 PM
Hi Dave,
Sorry for the trouble your having in the height of the driving season but this is usually when the problems show up.
A few suggestions to try if you haven't yet.
*Even though you installed a new fuel filter with the motor , very often a car that sits idle for a while will develope scaling on the fuel tank walls & gumming if old fuel has sat for over a month. I would change it, it's cheap insurance.
*Do all your testing with the points to eliminate any electric ignition confusion.
*The Weber downdraft carbs are mounted to a pierce manifold that is shaped like a sink trap. A rich mixture can puddle and collect in the manifold. I agree with Bill that this set-up is not optimal for the car , although the Weber itself is infinatly more adjustable than the Z's. I had spoken to a Weber tech some years ago & he stated this was not one of their better conversions. It was originaly designed to replace the Hitatchi emisions carbs on the Z cars. A good set of Z's or SU's should be your goal.
*It is a long shot but it's possible that your advance plate could be binding & not returning from an advanced position. These commonly become siezed. Check to see the advance with a timing light.
Keep us posted, good luck.

07-31-2005, 08:53 PM
The reason I went with DGV's, something I did about 10 years ago, was because the Z-S's that originally came with the car were of the early type, the type that were not adjustable, having been set, and sealed, at the factory. I did have them re-bushed and completely re-built to the tune of nearly $600 and the car still ran like crap. I have a friend in a nearby town who, back then, also owned a TR250 and he did the DGV conversion and he said it totally transformed his car. It was all I needed to hear. When I did my frame off, I spent so much money through TRF they gave me a coupon for 30% off any one item and I bought the DGV's. Back then, I don't think there was any possibility of using a triple set-up, like now, and I'm not sure there was much talk of using SU's, which I had on my TR4A and absolutely loved, because I don't think they mated up to the manifold. When I had the stock engine the DGV's were fine, never experienced any kind of problem; they were reliable and adjustable.
I have come to realize they may not be the right choice for the motor I now have. Lately, I have thought of digging out those old Zenith's, I still have them, as I think I read in one of Roger Williams' books or maybe Kas Kastner's that the needles can be modified to give a richer mixture, which I think was the problem I had years ago, running too lean. If what I've done today doesn't help I may give that a try again.
Mitch, you are right about fuel pooling in the "sinks". After pulling the carbs off this afternoon there was a pool of fuel in each of them. I saw on previous posts there was some discussions about limiting the fuel pressure when running DGV's and I can say I have smelled fuel a few times, like I remember when my TR4A's gas tank was seeping gas through the surface rust that had accumulated over the years. That's not the problem now, but it smelled the same.

08-02-2005, 01:35 PM
Check your OHM resistance on the coil. If it's below 3 then there is too much current flowing throught the points and cooking them. They will then start sticking and the jerking will begin. I had that problem with my TR4. It's an easy test to tell if you have the proper coil.