What type of spark plug does a 1971 triumph bonneville take?

the left plug problem indicates where the fault is
if you have duel carby , check for flooding in that carby

NGK Part # 5044 {#1262, 4525, 6824, 7051, B8EV, B8EVX, BR8EIX, BR8EVX} Iridium; Iridium IX
750 Model; T140V; Gap .024 CHAMPION Part # 88091 More Info {#8809, 88092}
.036 Good luck, Bill

180 DEGREES OUT OF TIME??? IF YOU HAVE SPARK AND FUEL. AFTER REMOVING ALL SPARK PLUGS HAVE SOMEONE PUT THERE FINGER OVER SPARKPLUG HOLES AND CK THAT PLUG IS SPARKING WHEN ON COMPRESSION "WHEN KICKING HER OVER". IF NOT SWITCH POINT WIRES GOING TO COILS.

http://www.jockeyjournal.com/forum/attachment.php?s=95a1978b89938c1b29fcb28a007b8a29&attachmentid=52901&d=1282943209

http://triumphbonneville120.co.uk/resources/Wiring%202-2.jpg.opt860x683o0%2C0s860x683.jpg

yes you need to remove the petrol tank

http://www.ngksparkplugs.com/part_finder/motorcycles/step4.asp?id=2576&type=reg

NGK says .035"

Hope this helps!

Bob

I'd guess spark plug range is your most likely issue. Unless you just have some loose wires - check for that first. Research your area's weather, and make sure to check with Triumph regarding spark plug recommendations. This information could be in your Owner's Manual. Always use plugs that match your riding style AND the weather. You shouldn't have to remove the ICUs in the winter. If you think you do, maybe check for shorts in the system. You shouldn't be getting any ground leakage at all.

No need to remove tank. I use an 18mm (i think) deep socket to loosen plug and slide a 8 inch piece of tygon tubing over the plug to screw it out. Insert new plug into the clear tubing to engage (start) the threads of new plug. Most hardware/home supply stores sell the clear soft plastic tubing very cheap. Take a new plug with you to get tubing that will fit snugly on the spark plug insulator. Tightend to specified torque setting and ride. Do not overtighten, as the aluminum head will strip easily.