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TR2/3/3A Correct spark plug for TR3

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bluemiata90

bluemiata90

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I have a 1961 TR3 with a rebuilt engine, Pertronix ign. and rebuilt fuel pump and carbs. The engine runs fine, but idles a little rough. Short of rebuilding the carbs again, I've repaired or replaced everything to do with the ignition system. My question is, I'm running with Champion L-10 plugs. If I switch to Champion L-11s plugs, will these plugs burn a little hotter to hopefully burn the excess fuel and maybe smooth it out at idle. I want to stress, it's just running a LITTLE rich and I've tried all the carb adjustments to no avail. If using different plugs isn't the answer, I can live with the way it's running now. /ubbthreads/images/graemlins/confused.gif
 
I know this doesn't answer your question but I've tried a bunch of different plug manufacturers and temp ranges to settle on a L87YC Champion Spark Plug. Then adjust mixture.
 
If it's running too rich, check to see if the step in the needles is flush with the bottom of the piston that moves upwards. You'll need to take the top off the carbs off and remove the piston and turn it over to see this. If they are too low, re-set them flush and re-test it. If they are flush, you could try moving the needles down about 1/16" at a time to make it all a bit leaner. Then re-test it by driving. I'd try that before changing the plugs or playing with the heat range of a new set of plugs.
 
Champion likes to change the number scheme every few years just to keep it interesting. Anyway, I've had no problem with L87YC (aka 312) though I like th idea trying to fix the problem thru the carbs, not a plug change.

Sometimes a rough idle is just a too slow idle -- our tachs aren't always precision instruments so if it is fine at all but idle you might check idle RPMs with a modern tester.
 
Hello BM,

Don suggests "If they are flush, you could try moving the needles down about 1/16" at a time to make it all a bit leaner" but it is far easier and more accurate to adjust the jet upwards.
You say, however, that you have tried all the carburettor adjustments so why is it still rich? Are you actually losing a cylinder or cylinders to plug fouling if so then maybe a softer plug will help. Could you be getting some oil into the cylinders at idle?

Alec
 
Thanks for all the replies. I'll give the carbs another try. As I did mention above, the engine runs very good, but just has a little miss at idle. I was just hoping that hotter plugs might clear it up. Thanks again
 
The following information is pasted from the Champion Spark Plug site and might clear up some confusion about "hot" and "cold" spark plugs.


"The term "heat range" refers to the relative temperature of the core nose of a spark plug. The words "hot" or "cold," when used in referencing spark plugs, are often a source of confusion and misunderstanding, since normally a hot spark plug is used in a cold engine (low horsepower) and a cold plug in a hot engine (high horsepower). The terms actually refer to the heat rating or thermal characteristics of the plug; more specifically, the plug's ability to dissipate heat from its firing end into the engine cooling system. A cold plug transfers heat rapidly away from its firing end into the cooling system and is used to avoid core nose heat saturation where combustion chamber or cylinder head temperatures are relatively high. A hot spark plug has a much slower rate of heat transfer and is used to avoid fouling where combustion chamber or cylinder head temperatures are relatively low. The primary means of adjusting heat range are by varying the length of the core nose and the alloy material used in the electrodes. Hot plugs have a relatively long insulator nose with a long heat transfer path. Cold plugs have a much shorter insulator nose and thus, transfer heat more rapidly (see illustration; hot to cold - left to right). The heat range of a plug does not affect the power output of an engine. Rather, it allows the plug to function as designed for the duration of the racing event. In other words, once the correct heat range is found that prevents fouling and does not contribute to the pre-ignition or detonation, a change to a hotter or colder plug will not have a positive effect on engine performance."

---Champion



Bill
 
Bill, very helpful. I was never aware of that and I've been back alley wrenching for over 30 years. Thanks for the info and help
 
New Old stock--They don't make that number anymore, but basically the plugs the same, but with a different number.
 
Hello BM,

is the L 10 a retracted tip style plug, you would be better with the more modern extended tip plug as they stay cleaner by being exposed to the flame. This also gives a wider heat range, these design changes are why plug identifications change.

Alec
 
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