Dommie same as XR650?
 

Does anyone atually know whether the engine in a 2001 NX650 Dominator is the same as the XR650? Honda says doesn't think so but isn't sure; the NX650 website says yes. Anyone know for sure? The reason is that I want to re-jet my Dommie having fitted a Pro-Duro exhaust and K&N Filter. Dynojet don't list a kit for a Dommie later that 1995 and don't answer emails, but the XR650 is listed. Can I use this kit? Anyone have any experience of doing so. Cheers.

I assume you're talking about the XR650L? The "R" definitely isn't the same - water cooled! I think the "L" is more or less interchangeable though, with slight difference to airbx / silencing arrangements, cam profiles / compression etc.

I'm using lots of Dommie parts to repair my XR/L engine, if that makes you feel better. I'm also certain that both Dynojet and Factory list full jet kits for the XR/L. Dave Lambeth will know for sure, but he's Rallye-ing at the moment.

Basically I'm 95% certain you'll be fine.
http://www.horizonsunlimited.com/ubb/smile.gif HTH

Rejetting these bikes is very simple, if indeed the same CV carb is used on the dommie as the XR650L. I don't know what's in the DynoJet kit, but here's what you need to do after 'uncorking' the bike:
Bigger Main jet - 155-160 seems in the ballpark.
Biger pilot jet - 55 seems to be what people have luck with.
Put a washer under the needle to raise it up a bit (not sure what thickness) since the needle isn't adjustable.
If the carb has a tab on the idle mixture screw, you need to grind that off, otherwise you can't give it more than one turn. You'll probably need to go a couple turns out. The US XR650L has that tab, don't know if the Dommie does.
Lastly, you'll need to drill holes in the slide so that it'll open faster.

I'm pretty hazy on the specifics of the hole size, washer thickness, etc. But try BajaDesigns.com - I'm certain they'll be of help and can sell you their kit. Shipping overseas should be fairly cheap, since it's very small.

engine seems identical to me, but not sure the carb is the same and the exhaust is definitely different. that said, you're replacing the exhaust so go for it, but keep an eye on plug colour/heat range

drilling holes in the piston ... I did, but I'd say the kit 5/32 drill is too big so I put one back to normal size using a modified sleeve from a pop rivet (fiddly!!!)

I did the kit (including drilling the slide) on my bike and it made a big difference. For use at home I was also knocking about with a K&N installed; this will be a TwinAir foam element when I'm on my way. Drilling the slide primarily increases "pick-up", in my experience.

Oh yes, and make sure you tell anyone working on your bike not to just "tune it to the max" or you'll end up with a very powerful but highly-strung engine. The idea of the BD kit is to de-restrict the lump, not to make it a fire-breathing beast.

Do I remember rightly that the stock US bike makes about 28bhp? Ridiculous! I think after desmogging and jetting mine was making about 51bhp-ish, and it was much too highly tuned (screen over airbox and holes in side-panel).

Of course, all that's a-changing now... http://www.horizonsunlimited.com/ubb/frown.gif

51bhp? I would expect it to blow up by mid-late forties and wonder if someone mis-read the dyno. the guy at PDQ races an XRR (not XRL) in supermoto and he said 50-55 is the limit for reliability. for comparison, mine reliably gives 31-32bhp and, while hardlybreathtaking, is good for 140kmh fully laden on gravel tracks.

<ahem> - you trying to be funny? http://www.horizonsunlimited.com/ubb/wink.gif The rebuild is continuing apace, and I should be back up and running with the XR/L by XMas. As soon as it's run in I think I'll go back to the Pyrenees and Andorra, to exorcise those ghosts!

Good news is that just before the incident I was pleasantly surprised (amazed actually) that, even with all of my crap installed, the bike was handling really well, even off-road. The major issue I had at the time was the noise, as I was using an XR400R White Bros race can, which was (understandably) rather loud, being essentially a tube not much bigger than a tin of beans!

While the bike's being reassembled (mostly by DL) I've made some tweaks to the luggage and instruments - love that IMO, btw - and acquired some ex-Desert Riders odds and ends, including a very nice extended bashplate.

To be honest, I can't wait to get back on board, but I'm having to work all the hours there are, which includes lots of night work, to pay the bills. Frighteningly I'm approaching the point where it would have almost been cheaper to use a brand new bike!

This is the bike, sort of ready to go in Brittany. That day we got as far as teh Pyrenees without too much effort. Next time I think I will take different sprockets for the European road legs; at 80mph I felt the XRL was straining much more than the F650 I was with. Giving the Honda longer legs for the motorway isn't exactly brain surgery and would keep the revs (and possibly mpg) that bit lower.

http://www.geog.ucl.ac.uk/~lmiller/boxes.JPG

nope, not trying to be funny, but being brutally honest: a standard, derestricted XRL only makes 31-32bhp at PDQ. if you remove the baffle, it doesn't change the max power but provides a 20-30% increase in mid-range torque which is worth something but not quite so much noise!

Well, if the standard XR650L only makes 31-32bhp then I don't think I'll bother rejetting the Dommie. Even with standard exhaust and air filter mine made 41bhp (exactly as specification). By re-jetting I was hoping for better mid-range (more torque) so that I could run a smaller rear sprocket and improve mpg. Maybe I shouldn't worry! Jeff

I should have pointed out that I had an MT21 rear which would have cost 5-10% (ie XRL approx 33-36 with road tyre). it'd be interesting to put the Dommie and XRL on the SAME dyno as I doubt there's 10bhp difference. PDQ had expected mid-30s rather than low 30s, but 41 spec is probably not 41 on PDQs dyno - they reckon bikes almost never hit spec.

I might be missing something here, but raising the gearing for improved MPG seems like a good idea on the NX, which is comparatively short between the ratios(maybe an extra tooth on the front to put less strain on the chain). However, altering the jetting to allow more fuel through could defeat the object. Unless you want to pull a higher top speed more than gain MPG. It might be a good trade off, though. I run an extra tooth on the front sprocket of my Transalp without any engine tuning. To be honest it doesn't seem to have made much of a difference, but it's not so good off road now......

Now here is a question for everyone: Why, WHY are motorcycles so damned uneconomical these days? The magazines seem to regard 40 mpg as economical - most cars of twice the weight can better that, so I don't follow their logic........

It's mainly down to throttle control. In normal use I get between 117 & 135 miles before hitting reserve on my GSX-R1100 if cruising at about 85mph on a motorway. I once rode from Oldham to Oxford without exceeding 85mph but when accelerating to overtake, I only opened the throttle slowly & just enough to allow the manoevre. This resulted in 173 miles before hitting reserve.

I've done the same on various bikes (R80GS, K100, DR600) & had similar results. Try it for yourself. You really notice the difference on a long haul, especially in fuel costs.

Steve

a guy in the tuning department at Rover once told me that you get the best mpg by operating at the revs that would give peak torque on full throttle. so, gearing to run at lower rpm means less efficiency from slower turning engine and, hence, potentially worse mpg. ie I don't agree with gearing up for lower fuel burn and I agree it can put more load and hence wear on the chain. my xrl chugs at below 100kmh in top and so I usually change down to cruise at 90kmh. even then, I only get 62mpg and I used to get 65mpg when being gentle with my ZX9

Presumably the 51 horses are 'at the crank' not the rear wheel. I wouldn't get hung up on the power figure they quoted - different dyno's vary fantastically. However, if they can show you their calibration certificate (traceable back to national standards) and they removed the gearbox drive and directly connected to the end of the crank then it could well be accurate ;-)

Dyno's seem to be useful tools to help tune a bike or establish if a modification has made a difference to rear-wheel torque - and the power output figure (that is calculated from the torque).

Unfortunately while a single dyno will fairly accurately be able to give a reasonable comparative difference between 2 runs on the same day (given the environment including tyres remain the same), the use of scientific units (ie hp/kW/etc) in their results is at best a rough guide, at worst misleading. (These guys really ought to specify a tolerance on their figures like 51hp +/- 25hp!)

Now, if it does give 51hp at the back wheel I guess the ability to carry spare tyres or find new ones en-route is going to be a significant limiting factor for any long trip. I've got this problem with my XR650-R which is alledgedly around 40 rear wheel horses - knobblies last around 200 miles (having fun), MT21 around 1000 (being careful) and Avon Gripster has potential for 2500+ but is road orientated with a thin side-wall.

Ian

good points,Ian. tyre wear is an issue even with only 31/32 at the rear. 6500 on MT21 is a pain in africa. I ended up on a 110 section trail tyre for one of the worst roads and it would have lasted 6000km so travel light and be prepared to have to put cheap stuff on ($23!), but remember to buy a smaller tube as the 120/140 heavy duty won't like being in a 110! there's another thread on tyres in sub-saharan africa that would be worth reading when planning an african sojourn. me, I want to try the MT70 and get some of the IRCs that came with the XRL: they were ace on MX track and great on the road.