Expansion chamber mod

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ivan H

Member
Oct 8, 2011
622
1
16
australia
With a stock head most people use an NGK B5HS or B6HS, or for a very slight compression increase u can use the extended tip BP5HS or BP6HS. Generally, if the end 3 threads on the plugs thread show blackening from heat ur using the correct heat range plug. Cheers
 
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ivan H

Member
Oct 8, 2011
622
1
16
australia
BTW, the heat range of a plug isnt about its ability 2 produce a spark, its its ability 2 transfer heat from the combustion chamber (actually, the plugs center electrode) 2 the head. A colder plug transfer more heat from the chamber & actually needs more heat generated in the combustion chamber 2 maintain proper operating temp & burn off oil deposits. Using 2 cold a plug will cause it 2 not light off properly & fouling. Using 2 hot,,, well, u can imagine. Cheers
 
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LaLongueCarabine

New Member
Aug 15, 2011
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United States
ivan H said:
BTW, the heat range of a plug isnt about its ability 2 produce a spark, its its ability 2 transfer heat from the combustion chamber (actually, the plugs center electrode) 2 the head. A colder plug transfer more heat from the chamber & actually needs more heat generated in the combustion chamber 2 maintain proper operating temp & burn off oil deposits. Using 2 cold a plug will cause it 2 not light off properly & fouling. Using 2 hot,,, well, u can imagine. Cheers
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Wow, thanks another misconception to the list!

Now that I'm thoroughly confused, my plug is chocolate colored and I have stalling and power loss at WOT.

I'm thinking I'm slightly rich because I use synthetic oil so shouldn't it be grey?
But it seems likes it's starved of gas, but could I be going the wrong way?
Stop drilling my jet put in a small one?

Also I'm still using 20:1 although I'm fairly sure I'm broke in.
 
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ivan H

Member
Oct 8, 2011
622
1
16
australia
I've never used synthetic, I like 15 or 20% castor/mineral, I guess from being an oldtimer, so cant say. But do a plug chop in the area ure having trouble with. Put a new plug in, bring up 2 temp & do a long enough run 2 get color on the plug, keeping in the area giving probs. Then with throttle still in problem area, pull clutch & hit kill at same time. Let cool & check plug, it'll tell u which way 2 go. Cheers
 
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