Hey, Henry here out in Ptld., Ore. The main plug is on the bottom middle facing the ground, of course. 17mm. socket is the right size, I think. I´m on my 2nd. helix, the 1st., a ´87 with 9500 miles on it; paid $1k., rode it 8 years, finally sold it last mo. on a whim- sold it to a 76 year-old guy @ 26k. miles- no trouble- new clutch at end, though(about $1100 bill) but sold it for $2200 so it was a great scooter! Had bikes for 25 yrs., it was my 1st. ´scoot. LOVED it! Just bought a yellow 2004 helix. Dealer had it from a repo. Miles? 74! amazing- has a carb.miss, tho.. Always had old bikes- the ´87 was modern for me, ya know? Then,found deals on craig´s list/ ptld., so quickly got a 2008 burgman 400- black, fast- goes 90 like the helix goes 60 m.p.h.., then a 2007 yamaha fz-6, then the honda last wed.. The fz6 had 200 miles- poor man dropped dead. Sorry, anyway, yeah, about .86 of 1 qt. of oil will fill the 250´s eng.. Clean the screen, too. Good luck, let me know- happy riding!!!! Henry.