yeh, check corrosion of dizzy cap,
check points gap and timeing aswell
for such high octane i assume you are running fairly advanced timeing?
do you always run 98 octane?
because if you usually use 91 and went to 98 and expected it to run better then you should think again, you will need advanced timeing to make 98 octane work properly.
also another thing that I'm not sure if it is, but by my crackpot theory could be, your mix is too lean.
and when you accelerate not enough petrol is being put in causeing it to chug and overheat,
my ke70 was chugging and shit similar to this,
i set points gap and timeing and all is good now,
also don't just assume that stock timeing is best, if you know how to adjust it just muck around with it, change it, go for a drive, change it, go for a drive
trial and error