The 85 250es is very temperamental when it comes to the CDI, I have tried many variants of different CDI's on mine and she just didn't want to run right, the only one I could get to make her run right was the CDI from Mike's ATV: https://powersportssurplusllc.com/sh...atc-250es250sx
I had to change out the original plug but that was easy enough, haven't had a problem since as she runs like boss. Been running this CDI for 2 years now, problem free and she starts right up every time.
1983 Honda ATC250R
1983 Honda ATC200E BIG RED (sold)
1984 Honda ATC200X (sold)
1985 Honda ATC250ES BIG RED
1985 Honda ATC70 x 2
2001 Honda TRX90
2004 Honda TRX300EX (sold)
2008 Honda TRX250TM
1976 Suzuki RV90M (sold)
1967 Vespa Primavera 125
1958 Massey Ferguson 35