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XR600R - The Camel Build Blog
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Refreshing The Camel
Coming up to its 18th birthday The Camel decided to take up smoking. Heavy drinking (oil) soon followed. With a sooty plug and increasingly sketchy starting it was time for an intervention.
To cut a long story short The Camel was bored first oversize, valves and seats were refaced, valve springs and seals replaced and a Stage 1 Hot Cam (gotta love that branding) installed.
The Stage 1 is a pretty mild profile that works with stock springs. It’s reckoned to improve mid-range and top end, but in The Camel’s case it was more about an easy way of eliminating the auto decompressor than chasing power.
Other than a copper head gasket, the cam was the only non-Honda part used – the thinking being that if things went pop in the middle of nowhere sourcing parts would be less of an issue.
1000km later the bike is running strong, starting easy, using negligible oil, and providing all the fun (and more) Honda promised back in the nineties.
There’s some handy engine rebuild hint here.
Over tyred and showing off...
The Camel covers more miles on tar than dirt, which probably explains why its ‘dual purpose’ Dunlop D605s were looking sad – scalloped on the front, squared off and close to the carcass at the back – after 2200km.
For 50/50 rubber the D605s work pretty good, but only getting a dozen or so decent rides seems a bit rich. Replacement rubber needed to last longer without moving too far from the dirt end of the spectrum. Heidenau’s K60 Scout has been getting some positive reviews, so that’s what went on.
The K60s have plenty of edge and fairly wide block spacing, but with a chevron pattern and less aggressive side lugs they’re more road-oriented than the D605s. The totally unscientific thumb-nail test also reveals the Heidenau’s have a significantly harder compound.
Honda cites 3.00x21 (80/100x21) for the front and 4.50x18 (110/100x18) for the rear. Heidenau’s 90/90x21 is the only choice for the front (that’s okay, it’s right for the rim size and ‘theoretically’ only 2mm more in diameter), but the rear is a bit more problematic.
A 4.60x18 is the ‘go to’ tyre for big dirt bikes (that’s what the rear D605 was), which equates to a 120/90x18. Heidenau apparently makes a 120/90, but the only available options at the time were a 120/80 or a 140/80. Working on the ‘bigger is better’ theory, a 140/80 went on.
The 140/80 clears everything, but height could be a bit of an issue. Honda's 'preferred' 110/100 has a (theoretical, these are just tyre chart references) diameter of 677mm, a 120/90 (4.60) is 673mm, and a 120/80 is too 'short' at 649mm. The 140/80, meanwhile, has a diameter of 681mm.
That doesn't sound much different, but the 140/80 works best on a 2.50 rim and while it’ll fit on the XR600R's 2.15 rim it ‘crowns’ a bit and gives a bigger diameter. The upshot is that an already tall bike sits even higher.
That said, there’s nothing to really bitch about. There’s some fiddling with tyre pressures to be done (currently 21/21 psi on tar), but at 400km the K60s show negligible wear, road manners are good, they track well on high-speed gravel and, aside from some lingering doubts about sacrificing 'stickiness' for the hard compound, all seems well.
Rain and mud are still to come, so time will no doubt answer compound questions. More later when the K60s have more miles under their belt.
Considerable fettling and fine-tuning hadn't completely eliminated The Camel's hanging idle issue so, rather than lose riding time, the decision was made to refurbish a spare carb and swap it in.
The 'second' carb was given a good soaking and a thorough blow through with compressed air, with meticulous attention paid to the various orifices and passages – particularly the ACV.
The slide and barrel were then lightly polished (using a Dremel, small circular buff, and only-slightly-abrasive Autosol chrome polish) and reassembled (Allen heads throughout) with care to eliminate any possible air leaks.
In an unrelated but possibly relevant exercise, the throttle twistgrip was taken apart, cleaned, lubed, reassembled and cable play set to spec.
Dropping the lower part of the throttle housing gives a clear view of slack in the cables, so it's a great way to start setting up play at the bars (after adjusting at the top of the carb of course). Getting the Phillips head screws out was a chore, so they were replaced by stainless M6x15mm Allen heads with a light smear of anti-seize.
So, compared to the v1.0 carb, the v2.0 carb basically got a polished slide and barrel and a far more thorough clean-up and re-assembly, but not the 'hole in the slide' mod.
After a bit of fine-tuning (a play with the pilot screw and down a size on the slow jet) there's no trace of a hanging throttle and The Camel runs strong.
Good work then, but a few too many variables to really pin down exactly what cured the hanging idle. For a more detailed analysis of hanging idle issues – and a handy list of sizes to replace those nasty cross-head screws with a shiny new set of Allen heads – check out the carby tips page here.
A certain ratio...
Juggling The Camel's jetting required some wide-open-throttle work, and that showed up another area for possible improvement – the gearing.
Set up for the road with a 15-tooth front sprocket and a 43-tooth rear, The Camel was relaxed at 110km/h in fifth gear and would hold 140km/h for as long as you were game to hang on.
However, on WOT runs The Camel wasn't keen to go much faster in fifth than it was in fourth unless you had plenty of road and were well tucked in. And that, together with a lack of the typical XR600R wheelie-at-will response in first and second, suggested the gearing could be lower.
Standard XR600R gearing is 14/48. Honda describes 15/48 as the 'highway' option, so that was a good place to start. And it was as far as pulling wheelies went, but at 110km/h The Camel was buzzing way too much for more than just short bursts along the highway.
Going back to the 43-tooth rear with a 14-tooth front took fifth-gear rpm at 110km/h down to acceptable levels, with the added bonus of a nice strong 80-120km/h roll-on – good on the highway and just right for whipping past people dawdling on country roads without dropping down a gear.
It's no trials bike, but it'll idle along happily at a walking pace in first and loft the front wheel on throttle alone. A pretty good compromise for a bike that sees more tar and fast gravel than tight forest trails.
Of course, finding all this out meant pulling the rear wheel off twice and lengthening and then shortening the chain (whose idea were press-fit master links anyway). Would've been much quicker to just work it out with the handy gearing guide on the Chaparral Motorsports website that you'll find here.
Camel update: more fun with jets
With other projects (like the Triton) on the go it's been a long time since The Camel build blog was updated. Save for new fluids, a new taillight globe, and the quick addition of a camel graphic on the headlight shroud, the bike's just been ridden and enjoyed...but as spring turned to summer the urge to really sort out the jetting grew strong.
Cold-start issues back in winter (see below) led to jetting changes and carb mods aimed at curing a hanging idle, but there was still a suspicion it was running too rich. Trying a 'leaner' #65 slow jet resulted in a pale plug and a high hot idle, so the #68 went back in.
Swapping the #160 main jet out for a #158 made more of a difference – the bike ran significantly stronger at the top end. All well and good then...at least for a few weeks until a slightly dark tailpipe and a nagging memory of the 'racer recommended' #155 main started to take hold.
In a 'give-it-a-try' moment the #158 came out and the #155 went in. Not as big a change as the move from the #160 to the #158, but the mid-range response and top end seemed a little better. Paranoid about going too lean, the plug was pulled after a series of progressively longer test rides showing a good 'light tan' colour ('mocha' for hipsters) with a mid-grey tailpipe.
Air temperatures are higher now than they were with the first round of jetting changes, so the best 'all-round/all-year' set-up is probably somewhere between the #155 and the #158 – which means playing with the needle clip position...but that can wait a bit!
In the meantime, it looks like this page has been getting plenty of hits and it's a fair bet they're from XR600R owners with issues like poor starting or a hanging idle. So, rather than take up space here, click on the link below for a "what we've learned so far" run-down on solving XR600R carb issues.
Cold (carby) case
Winter cold-start issues prompted a closer look at jetting. Fiddling with the pilot screw didn't make much difference so that led to the 'lightbulb' moment: the air filter had been heavily over-oiled so maybe cleaning it out in combo with lower temperatures meant we were running too lean at idle.
Stock XR600Rs run a #152 main and #62 slow jet. Racer recommendation for 'uncorked' XRs is generally 155/68 . This one had a #160 main and the stock #62 slow jet – too lean down low.
Thorough carb clean, gaskets, rubbers and float bowl checked, a #68 slow jet, a set of stainless Allen heads to replace the rounded Phillips heads, and it's starting fine.
And what better time to address the other carb issue – a sticky throttle. That big piston produces a lot of suction when you throttle back and the slide tends to stick a bit giving you a hanging idle and jerky off-throttle response. The solution turns out to be drilling a hole in the front of the slide to reduce the vacuum (courtesy of a German website – complete with diagrams – that XR600R owners with the same problem will find here).
All good then? Well, the throttle could feel a bit lighter and it could possibly go down a size again on the jets. Tailpipe colour looks a little bit dark, but it's running pretty good, so maybe wait until next time the tank comes off.
The fun begins...
Old trail bikes are generally run ragged but, bought just before it turned 16, this 11/98 model hadn't been...err, well it was well cared for despite obviously having been ridden and enjoyed in its natural environment.
Nice touches (kudos to previous owners) included Acerbis handguards and disc protector, alloy bashplate and front guard stay, Works Connection side guards, XR's Only chain guide, gripper seat cover, a full FMF exhaust system, and the news that it had been 'uncorked' (XR600Rs came from the factory with a restrictive inlet manifold) and that a billet choke butterfly had been fitted (as opposed to the designed-for-disaster multi-part stocker). Even came with the stock rear light and mirrors!
A few shakedown rides showed nothing not already hinted at – the missing muffler end-cap proved deafening and the squared-off rear knobby made cornering on tar more exciting than it needed to be.
Spanner time: general service, various dodgy fasteners replaced, stock rear light and fender swapped for aftermarket units, 'sharkfin' disc protector added, indicator mounts reworked to really tuck them in, wheels swapped out for polished units with Dunlop 605 (50/50 road/offroad) rubber, new chain and gearing at a highway-friendly 15/43, front end dropped down a bit for sharper steering, expandable tool bag installed, old FMF can replaced with a Staintune muffler, and that big 22-litre Acerbis tank bolted into place.
Looks good, rides right...ready for adventure or the zombie apocalypse.
Keep your cool!
Heat is a killer on XR600Rs, so it makes sense to keep things as cool as possible. Adding an oil cooler is an option, but there are a few things you can do without spending any money or adding any complexity.
Air is free (at least so far), so to improve airflow around the engine and oil reservoir 75mm was trimmed off the back of the front guard (with the aesthetic bonus of lining up nicely with tank), the 'blanket' over the top frame rail consigned to the parts bin, and the front of The Camel's shiny aftermarket bashplate heavily ventilated.
Definitely looks cooler, but to keep an eye on actual temperatures a JMP oil temp gauge was ordered up on eBay. Unfortunately the gauge didn't go in until after the modifications, so there are no before and after figures. That said, The Camel sits around 80oC at a constant 80km/h and 100oC at 100km/h against an ambient of 12-15oC (winter) with a 10 degrees or so increase in correspondingly warmer summer temperatures. All good then!
Couple of notes about the JMP gauge: it's a lot more fiddly to get in and out than the stock 'eared' dipstick, it doesn't have any markings for checking oil levels (solved by media blasting the 'probe' to match the Honda dipstick), and the fluid inside (presumably to damp the needle) seems to be slowly leaking out. It's still working fine after a few months though, so at around $50AUD it's cheap insurance against cooking the engine.
The photos show a comparison between the stock parts and the modified items...Tasmanian Racing Chickens (aka Native Hens Tribonyx mortierii) don't look impressed by the improvements though.
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