DRZ 400S initial engine mods finished

Hi I have just successfully completed a successful transformation of my old road legal S, from a torquey but slow old bike to one that hauls. It has been fitted with a genuine secondhand DRZ E FCR carb, removed the overun enrichener and linked the carb fittings with a tube, 55 pilot, NCY-T KXF 450 F needle, 2 turns fuel screw, 168 main jet, new valves, cleaned up combustion chamber and ports, concentrating on the valve pockets and the bowls behind the seats, 13.5 to 1 wossnier piston with the s model base gasket to drop compression for pump gas, E model exhaust B cams on both exhaust and inlet (244 dur and 9.3mm lift on both), had to degree the inlet cam and fit the proper inlet sprocket with the correct timing marks, decomp removed on both cams, also had to grind of a bit off the shaft where the decomp was to allow fitment to the inlet cam bore in the head,ported E model header with a 2005 rmz 450 oem muffler and fabricated link pipe (made out of the pipe off the original muffler), std CDI unit, foam twin air filter with massively opened up airbox, NZ 95 pump gas, 190 cca battery, I modified original screw camchain tensioner into a fixed manual tensioner, all locktite mods done, standard s gearing.

It runs way smoother, better fuel economy, starts instantly, idles happily round town, great on the dirt, massive fun on the road, comes up in the first 2 gears on the gas and third with a tug on the bars, and Im 115 kg (240+ pounds), easily does 145kmh, no effort has been put into taking weight off the bike at all.

Next job is to fit the CBR 250 17 inch rims for road use, the gold valve/respring the front and rear ends of the bike, and I need to lose some weight.

Thanks heaps to all the DRZ 400 posts on TT, been a great source of info, the B cam mod is unreal and has transformed the bike, they are close to the old stage 2 hotcams, just 10 thou less lift, its smoother and carburates almost perfectly, will get a dyno print in the next couple of weeks. Thanks for all your info.

Well done bro! How about some pictures? The dyno run would be interesting.


Good to see more Kiwis posting , I'm an expat Kiwi - hence the Avatar!

Yep, people said the E ex cam mod into an inlet was risky, took a bit of fiddling but it has transformed the bike, honestly the bike is not worth putting on the net, looks like a tidy but well worn S model, will do once the dyno print is done and CBR rims are on, the RMZ muffler looks like it was made for the bike, too easy to fit really, thanks for your positive post, and good to hear from another kiwi, cheers

How do you attach pictures in posts?

Think you need to set up a photobucket account then paste in images form that ....looking forward to the dyno curves!

Excellent! Very inspiring to see some deep work on the bike!

very cool.  Im not sure i would waste time fitting an rmz muffler when using the stock header.  thats the bottleneck.  is your actual compression 12.2:1 ?  I know those 13.5 pistons assume the single layer gasket. 


have you run an e intake cam to feel the difference?  interesting stuff!

Good for you man. Get it all done then ride,ride,ride! :D

Yep I had the A inlet cam in, it ran really good, now the B exhaust cams in its place the bike has come completely right from bottom to top, there may be a slight bottleneck in the header (e model one) but this setup is fine with the bike still being 400cc, the NCY-T needle is unreal, I tried to do the upgrade with as many secondhand bits as possible to keep cost down, tracking down e model bits is difficult, only new bits were the needle, piston, valves gaskets and manifold, yep the compression is about 12.2 - 12.4 to 1, the chamber mods and S base gasket would have dropped it over a point, I will post photos of my cylinder head mods, cheers

By the way the Americas cup is bloody depressing

Getting on the dyno on Tuesday, I well rejet the bike againover the weekend, will put the needle to clip 3 or 4, and lean up the main jet, I have a few to experiment with, got a 150, 155 and 160 to try, ECY-T needle is good but is rich right through, the response is worth it, should have abandoned the DXP needle from the get go, hence why it was at clip 6 and 175 main, the 168 mj is still to rich, and it not as crisp up top as it should, 55 pilot is perfect at 2 1/2 turns so that's ok, having free access to a dyno would be awesome but at $150 NZ dollars a go (about $120 US) I want to do it once, hence why I could not afford a baseline run, but I have many other dyno comparisons of other bikes on the same dyno, so I may be able to deduce a difference from that, I reckon the bike was not much more than 30-32 at the rear wheel, well over 40 now, cheers, once the 462/rhc cams/o/s valves/41mm fcr/MRD is done then I will do it again, but the suspension will be gold valves and rebuilt, linkages and bearings checked/replaced, the motard rims fitted, some case plates fitted, pack rack and a decent seat will be put on before any more engine mods take place, the bike does an easy 100mph now with me one the tank with trail rims, Im 6ft 1in and 115kgs, so thatS pretty good for a stock bore S, and I could lose my license with that, will post results, if I can figure out to upload photos.

By the way the Americas cup is bloody depressing

Aussies were involved

Its calling clutching defeat from the jaws of Victory, idiots, I reckon the Oracle boss man paid the magician dynamo to make invisible a couple of 350 verado outboards, the change on boat speed was pronounced.

Final jetting specs, FCR Slant carb, 55 pilot, 1 3/4 turns fs, 150 main, NCY-T needle 3rd clip from top (could accept posn 4 methinks), all air jets as per std early E model, may need a tiny bit of main say 152, dyno a/f ratio reading will tell the tail, but it carburates stunning everywhere, up top, going thru town in top, accepts the throttle being wrenched open at about 4 grand in top going up a slight hill, on the paddocks the first four gears are spinning the rear right to the limiter, very happy with it now, leave well alone (fiddling is addictive), suspension and comfort mods are next, cheers



Hope this works, pictures of my heads mods

DRZ <a href='https://thumpertalk.com/link/click/4478/' rel='nofollow' data-ipsHover-target='https://thumpertalk.com/index.php?app=autolink&module=links&controller=content&id=4478' data-ipsHover target='_blank' data-autoLink>Exhaust.</a>JPG

DRZ Cyl Head.JPGDRZ <a href='https://thumpertalk.com/link/click/4478/' rel='nofollow' data-ipsHover-target='https://thumpertalk.com/index.php?app=autolink&module=links&controller=content&id=4478' data-ipsHover target='_blank' data-autoLink>Exhaust.</a>JPGDRZ Inlet.JPG

The exhaust port has been lightly tidied up, the hole for the EGR has been filled with very high temp liquid metal (1200 deg c) and smoothed back, most of the work is in the bowls behind the seats and valve guides, the inlet has been tidied up heaps with a nice swirl with a stone to promote mixing, the bolt on the inlet tracked filling the holes run flush with the tract, i.e. smooth with no holes, heaps of work behind the seats, the chamber has had the inlets and exhausts unschrouded, and line up with the edge of the bore, just clear of the gasket, this will change again once the 94mm bore gets installed, all the machine ridges have been blended back and all the transitions between the seats gently smoothed, naff all metal was removed, finished with 1200 grit, took 8 hours work. Cheers

what did you use to remove all the carbon?

Nothing, just water blasted the head and started chewing away, the carbon was a handy reference to show me where I had not been, cheers

And the mods continue, the RMZ muffler had a cork in terms of the 35mm outlet, that been rectified with a 42mm outlet piece, muffler has cost about $80 bucks so far, it is fair quieter now, yet to ride it but I suspect the main may have to go back up to a 150 and clip 4 from the top on the needle, cant wait to try the new 43mm aftermarket header, cheers

Muffler 1.JPG

Muffler 2.JPG

Muffler 3.JPG

Muffler 4.JPG

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