F5's 300 head mod thread

[(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]

Originally Posted by 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."

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.