F5's 300 head mod thread

[motopsycho87]

I machined my squish yesterday down to 1.2-1.4 (measured with blue tac so only so accurate!), I was running 0.5mm base gasket before, I've just bumped up to 1.5mm base gasket (to get ports to line with piston flush) and reduced the squish. The difference to the bottom end is insane, far more powerful (counter intuitive considering raising the exhaust port etc benefits higher revs more), BUT, I have actually lost a bit of top end (I did machine out for same cc in head), this has lead me to believe that perhaps before I had jetted rich to compensate for the bad squish (I was running 2.6mm), and now it is corrected, the jetting is too rich. This would bring me to a 175 main jet which is in line with a fair few people's bikes (I would go out and mess around with it now, but I am hungover and it's pissing it down outside , fair weather much lol!), would be interesting to know if you found the same with jetting?

[(F5)]

Yeah I'm running a 178 & have been meaning to try a 175, but just a bit lazy on that front. Once you get to a ride you ride a loop & then either go out for another loop, or have lunch. The bike is dirty & you are tired, about then people say, ok lets do another loop.

. . .so do I get out the tools & perform carbadectimy in the dust? Nah, just ride. Actually we were on the grass under the shade of a line of trees (summer here), but still couldn't be arsed. Actually I'd not packed my jets come to think of it.

This morning I was thinking it may be easier to find an old 18" tyre & throw it o the dyno I have access to.

[Jakobi]

The latest 2013 that TSP setup the head on, and then tuned on the Dyno ended up with 40 NEDJ#3 (or NECJ#3) and 168 main and was sufficiently rich off the bottom end. Thats on a PWK AS2 38mm with leak jet.

On my 2013 250 I'm at 175 main and think I could probably drop one more yet.

[hannesd]

RE:
"I've just bumped up to 1.5mm base gasket (to get ports to line with piston flush) and reduced the squish. The difference to the bottom end is insane, far more powerful (counter intuitive considering raising the exhaust port etc benefits higher revs more)"
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this gets me excited to find out what this would do to my ec 200!
but if this turns out bad for me, there aren't that many ec 200 to find a second hand head if i f*ck up... or if i want to make it undone... you can only take so much off the head right?

Hannes.

[motopsycho87]

You can always buy the S3 head with removable inserts. I took 2.2mm off my head with no worries whatsoever.



I put a 174 main jet in today (tried 172), they both feel roughly the same, 178 is definitely too rich as when you whack it wide open in neutral it 4 strokes and smokes like hell. I have gained a lot of low, mid and upper mid range power, but the bike feels flat on top (this is on the road, not the track), is this just the nature of the beast or is something killing my power?

[(F5)]

So have you checked the volume at TDC on the bike to be super double sure? What compression are you running? & on what fuel?

[wa_ndro]

Originally Posted by Jakobi

The latest 2013 that TSP setup the head on, and then tuned on the Dyno ended up with 40 NEDJ#3 (or NECJ#3) and 168 main and was sufficiently rich off the bottom end. Thats on a PWK AS2 38mm with leak jet.

On my 2013 250 I'm at 175 main and think I could probably drop one more yet.

wow, is that on a 300 Jakobi? That's the needle i'm using, but i'm at 175 MJ and pretty happy - tho this will prob change with the newly machined head.

obviously ~45:1 and ultimate 98?

[Jakobi]

I'm not sure who's bike that was that Dave was setting up, what the final squish or compression ratio was that it ended up at either. It was definitely a 300 though. I'm sure the post is on DBW somewhere but he has confirmed it on the phone for me too.

Mine is a 250 with 45:1 Amsoil and BP 98RON. Yep!

Edit: Found the post and quoting the man

"I recently did a 13 gasser 300, removed the high comp s3 head, installed the stock head again with corrected squish clearance, angle and comp ratio and made way more power everywhere. The main thing was that on the dyno I was able to drop the main from a 178 to a 165 and it ran brilliantly. Just pulled it down after 3 fairly hard hours and there's no signs of overheating or running lean. The rest of the specs were 40 pilot (runs rich down low, starts without choke, could get away with a 38) and necj needle #3 clip.

I'm not sure I'd try these on a stock head but it seems the gassers can take similar jetting to the KTM's when set up. Ill post up if this bike needs to be richened up in the future."

[StuJohnson]

Thanks Jake for that.
Very interesting setup. Where did you find that info? Would love to read more.


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[Jakobi]

There is not a whole lot more to read. Just a jetting thread on another forum where Dave chimed in as he'd just set one up on his dyno.

Now also keep in mind thats on Australian fuels and for some reason I have noticed we typically end up a bit leaner than US. The mods he has done are probably very similar as what F5 has done. Cut the band back to reduce the angle, reduce the squish clearance, and then open up the chamber to correct the volume. I'd ask Dave to chime in here in the thread but he's been seriously busy with work. Its hard enough getting a few messages back and forwards on the phone. Its also on the newer designed cylinder with the G stamped into the side of it.