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)"
.
.
.
.

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]

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.


Sent from my iPhone using Tapatalk

 

[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.

 

[(F5)]

ooh, interermisting,

I've found a hole in my Keihin jet range below 178 & above 165. I might just have to cash up & buy those jets & find an old tyre & dyno it.

38 on the Pilot? I've got a 40 but atm I've got idle wound in all way so I was going to try pulling the slide down so less influenced by start of needle, but I thought a 42 would have been the direction to compensate. I'm on a CEL (or was it CCL?).

 

[Jakobi]

Thats all on the newer AS2 carb with the shallow bowl F5. Seems to like much leaner jetting in general. They have a newer model AS2 on the 2012/2013 from what I can see too. My new bike has a leak jet. I have a pic of it somewhere but can't recall what number it is. The NEDx/NECx needles also supply a decent amount of fuel towards wot. They taper right down like a toothpick, where comparitively the N3xx needles are much thicker towards the pointy end.

Even with the two engines I have setup very similar in terms of base gasket and head mods, the port layout is different, the way they run is a little different too (same jetting specs, both running in sunshine mode). Slight differences in carb, different airbox, different silencers.

 

[(F5)]

Local shop sez they run most older on 175 on our gas, worth a try buying a 175 and 172 at least. Then try pilots and se if I can get idle up again.

 

[wa_ndro]

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."

thinking about this, i bet that bike was running the stock Q stealth

 

[Jakobi]

Its very possible.

What I have noticed with these engines is that its quite hard to get a main too rich to the point that the throttle just breaks up and burbles. I've had my bike do it with no main jet, and at 180 it felt fluffy up top (not crisp), but I imagine it would take quite a bit to get it blubbering away on the main.

I wouldn't be surprised if we could all drop quite a few mains to make peak power and max overrev, but honestly, how often do we spend at WOT, do we need the max, and is it worth sacrificing the safety buffer of richness?

 

[(F5)]

Certainly I spend little time tapped out. The only time I'm wanting is sometimes up a slight to moderate hill and I want to get a boogie on and whapping throttle wide, it's got a bit flatter than it was due to different fueling requirements now.

 

[motopsycho87]

put a 168 in mine, insane.

 

[(F5)]

Mine does have a 175 I just found (must update my notes). Oh well I'll buy next 2 sizes down & trial when I have a mo. (its an 07).

Does have a 40 pilot with airscrew wound out 2 turns so I may try a 38 & try get a higher idle with idle screw out a bit further so I'm not ont eh needle at all. Not sure if there is enough straight section on my needle or if I'm into taper but I think I had to drop the needle to run best so I could well be in taper.

Only drama is getting it hot to test it out where as most trails we set up & go for a long loop.

 

[motopsycho87]

I found the jump from 178 to 172 only have me more mid range. I was almost disheartened then put a 168 in and scared myself to death!

40 pilot, air screw 1.5 out. cek 3rd clip, 168 main

 

[(F5)]

Well ordered my missing jets. Will see if can get a skip bound tyre for dyno.