2018 EC250 squish, jetting & pistons

[Gibnut]

Posted this on DBW (I?m Or-strayan, moite)

I rode the bike after Dave at Two Stroke Performance, Victoria, (twostrokeperformance.com.au) re-cut my head - power was noticeably up down low & spooge was greatly reduced. The bike was, however, running on a little.

Jetting - NEDW #3, 45p/175m, a/s 1.5.

Squish - was 2.31mm, now 1.35mm. With squish like that, no wonder she?s a spooge-machine!

Note to all ?18 EC250 owners - before you get your head sorted (use TSP, Dave & Jason are awesome) you will need to accurately measure your piston crown height by taking the barrel off the bike, or find a way to measure piston outside edge to piston crown while the barrel is in situ.

Why? There are confirmed reports of 2 different pistons in the marketplace, one with a crown height of 3.77mm & one with a crown height of @ 4.5mm. This obviously greatly affects compression & therefore (combined with an accurate squish reading) your tuner?s ability to set compression as per order.

I incorrectly assumed, as the bike hadn?t been apart, I had the lower crown piston - as another rider had the smaller piston installed from new.

This consequently gave Dave no chance of setting a reasonable compression ratio as he was going on an incorrect assumption. Stock is around 13.6/1 but with the incorrect crown height factored in, it was actually closer to mid-high 14?s; too high for my jetting. And, too high for my riding style, reasonable fuel consumption (was going to have to go 48p/180m ) & motor service life.

Currently waiting on a solution - either retrofit the smaller piston (preferred, as the head is set up for it) or have Dave re-shape (at no cost) to suit higher piston.

Option ?a? is preferable for obvious reasons.

I must say, this bike is so much fun to ride & easy to work on but has been an absolute shit to jet. Now we know why! My mates mostly ride GG300?s & no-one?s had these issues.

Also, there were a couple of ?Friday arvo build? niggles to be found when I pulled it down, too - pv arm lock nut, rhs cover, had backed out all the way down & while checking for air leaks, found the reed block bolts were not quite tight enough.

Hopefully, I am close to getting this fabulous motor to it?s potential. On the ride post-head cut, I was climbing rocky lines in 2nd that would usually need first. And that was with a lean condition!

It?s instructive that, being the pragmatic person I am, I have kept the faith (I?ve had moments when I wanted to ?fix? the bike with a hammer..) - because, as anyone who?s ridden an ?18 Gas Gas EC will happily tell you, the frame, suspension, handling, steering & balance are worth it!