I was at the track and was watching a person with a J motor running around. now this person has experience with this motor. I asked him how come he has the motor 4 stroking at the end of the straight. his reply was the carby can only intake so much air hence the 4 stroke. now that in my limited experience with a j motor in my books don't sound correct. If its 4 stroking its not at its best. YOUR THOUGHTS PPL
Comments5
A 4sroke position at the very end of the straight, just as you dive for the brakes, is a SAFE tune, agreed probable not the quickest, but perhaps the safest?
Max.
This is a way of tuning a J. Get it to 4 stroke just before the end of the longest straight & lean off a tad.
+1 for both replies.
If he was running some high jet opening, I would look to lean that off first, as that jet has more relevance to the KT100S. Our method was to start on 2 turns out on the low with a light choking, and about half way round the lap, dial the low back to about 1.5 turns, as that seemed to be about ideal. By 10 laps in, the low will be progressively eased back out to about 2 full turns to maintain a good temperature, but still no 4 stroking.
when it comes to kt100j & s between different engine builders there will always be different views depending how they have the carby set.
Personally from my years of running j i would try to prevent four stroking. four stroking is effectively incomplete combustion, this is bad for performance and to an extent engine wear. if it is four stroking to the extent you can notice it then i would definitely be leaning the HIGH jet by the width of the needle and re-evaluate.
i used to run in practice of each track in the morning and pull the high open from my normal starting point once engine warm and at full throttle near the end of top revs until four stroking, then back it off a bit and then unless massive weather changes this would be the high jets setting for the day. i would then only use the low for tuning during the race.
the kt100s however due to the higher average rpms i used to use the high for tuning and the low jet only for rolling starts to prevent flatspotting.
only exception been the old oceania track at oran park or when we ran wakefield park where the little j would be singing at over 10600-11200 for quite some time. the high jet would be used during the race and a tonne of choke into corners
The high jet on the J is really only for show as it does not come into play until around 11,000 revs which is about top revs for a J. The same as you Terry,about 1.5-1.75 out on the low & just crack the high needle open.
ck. Terry Sheedy said:
+1 for both replies.
If he was running some high jet opening, I would look to lean that off first, as that jet has more relevance to the KT100S. Our method was to start on 2 turns out on the low with a light choking, and about half way round the lap, dial the low back to about 1.5 turns, as that seemed to be about ideal. By 10 laps in, the low will be progressively eased back out to about 2 full turns to maintain a good temperature, but still no 4 stroking.