Fine Tuning WR400 Jetting


My Euro WR400 has a #165 main, 42 pilot and a DRQ needle, 4th from top.

Stock exhaust which oddly says “Not for Road Use” despite being quite quiet.

Anyway, same as my WR450 from a few years back the stock jetting is very lean at low throttle and makes the bike run stuttery and snatchy,

Popped in a #170 and much much better, but then do some digging and find lots of stuff from Mr Dean about using a needle with more taper to increase mid-range:

and for some reason I can’t even recall I happen to have an EMN brass needle in me box of bits!

This needle has a steeper taper (first letter D vs E) and thinner straight part (last letter “N” vs Q), but the differences are quite small without comparing with a micrometer.

Put it in the bike (+165 main) and holy- sh** what a difference! The pick-up from low revs is verging on the astonishing for a mere 400 - I would never have believed a WR400 could have so much grunt! And the power just builds in one long arm-pulling surge to max revs, wow.

All very good, and the bike runs much smoother at low revs, real civilised. HOWEVER, the extra richness at low throttle has resulted in a slightly wooly pick-up from idle using only a small tweak of the throttle, like say blipping the throttle when down-changing at low speeds.

Crack the throttle more and the pick-up is instant, no bog, its just when you ride very gently its noticeable or say when trickling along at idle in 1st.

Still got the #42 pilot in, and fuel screw about 1 ½ turns out, but adjusting has no effect on my wooly problem. Funny enough I had a very similar problem with the WR450 when I richened up the low-end, though as that had more power it was not so problematic.

Any ideas? Smaller pilot perhaps?

It wouldn't hurt to give a smaller pilot a try. Have you messed with the accelerator pump timing at all? Maniac

Thanks Maniac.

Not looked at the AP yet but I can feel the rich woolyness on steady throttle, just off idle. I'm talking tiny throttle here, probably only 2000-2500 rpm or so.

Anyway, I have gone a different route and installed a 178 main! But not with the rich EMN needle but a slightly leaner-than-stock DUQ.

The 178 is *slightly* too rich on the over-rev so while it still "over-revs" and does't seem to have lost any power its perhaps not quite so crisp feeling.

Up to max power revs though it is superb! Just as strong as using the rich EMN needle, but has lost the wooly feeling at very low revs.

Its like a different bike, incredibly smooth and tractable at lower revs - super user-friendly but with effortless power with a twist of the throttle.

Interestingly my KTM400-EXC used a very similar jetting set up:42 pilot, 178 main and an even-leaner DVR needle, and that was one of the most perfectly jetted bikes I've ever had.

I think with this new set-up the WR has more power at all revs than the KTM, and even out-grunts the DRZ-E I had a while back - whooda thought!

Oh, tried a #175 main and while it was marginally crisper at max revs the lean snatchiness at small throttle was showing its ugly head again.

Really bizarre how this bike (and my WR450) seems to like a lean needle and fat main to make it run smoothly at low revs, i.e. when theory suggests the main jet should have little effect.

Well, it does...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now