I also chopped the airbox, hi-flow reed stuffers from Tyga, HRC electronic derestrictor and HRC front cylinder head modification and removed the air bottle below the carbs and plugged the holes with fat bolts, HARC-PRO chambers and cans. Using a BR9 plug.
I guessed at a 135 main jet, and used that for the engine heat cycling, then after it was run in I followed the instructions on the tuning page here and found it was fine holding at 4000 RPM but at 7000 RPM it would rise in revs indicating leaness. So I moved up to 140 main jets and it then held solid at 7000RPM. Went out for a plug chop and held it flat out in 4th probably for 10 seconds or so (all I could manage on local roads) and the front plug came up a light tan colour on the electrodes and the ceramic -defintely not white anywhere-. From the plug guides I'd seen this looked perfect, but not on the OK-but-rich side. I rode the bike on the road for 100km or so then went to the track and hammered it for several sessions and 3 fun races (won one of them too) -no monster long straights-. Somebody told me to check for crack-McPop from the exhaust on overrun after chopping the throttle from wide open (indicating lean) and I didn't have that at all. Decided to go and get it dynoed and do a plug chop on the way. On the expressway I had it maxed out at 10000-11000 RPM for a good 10 seconds in top gear throttle full open. Now I am not quite sure what happened because I simultaneously chopped the throttle, hit the kill switch and pulled the clutch ... but I got a rear end slide somewhere in there which I wasn't expecting. Thinking: hmmmm! Was that a seizure or just hitting the kill switch before the clutch?
So I stopped and pulled out the front plug and to my horror the ground electrode is melted and everything is covered in a grey furry deposit. Bike started up OK and rode home fine but would no longer idle, and compression seemed down maybe when kicking it over.
Hmmmm! I can't make sense of it, I was expecting a really white lean plug if it was a seizure. Looking at plug reading guides, the melted electrode indicates pre-ignition. Now I read somewhere that the HRC box advancs the timing ... And the furred up plug is due to addatives or type of oil used, which doesn't make sense. So I am guessing that the grey furry stuff is melted and atomised aluminium from the piston, but that seems a bit extreme.
When I get over the demoralisation I'll pull the front head and cylinder off and have a look in there, but either way it begs the question: how is a plug chop going to tell me I'm lean if it seizes the engine first? Or if I was so lean as to cause seizure, then should it not be possible to detect beforehand?
Where did I go wrong?
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MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-
