Slightly Cafe CB250RS Project

[tychver]

Had a CB250RS sitting in my carport for almost a year now waiting for me to get back from Germany. It's in a bit of a state. Mechanically it's fine, but the paint is shagged and the exhaust is HORRIBLE. Someone's put a coby resonator on there at some point!

My carb has 12.5kw stamped on it. Does this mean mine is still restricted? Where was the restriction in an RS?

Bike was running fine when I left, but after 3 months of sitting there it doesn't start. Didn't think flat battery would stop a kickstart but maybe it does. Ditching the battery soon anyway, and the airbox.

Niggling issue is the clutch perch is slightly chipped and doesn't hold the lever properly. Bike was dropped in drive by last owner and broke lever. perch and left hand side of the bars. Rest of bike is fine, but still crap lol. I'm going to replace the bars anway so I could replace the controls. Where the fuck do I get replacement/alternative controls?

Not done too much work so far:
Cleaned it!
Speedo, tacho and choke cables
Repainted rear brake pedals

Planned next:
New tires! Current are WOFable but shit. Reccomendations?
Remove battery and side pannels
Remove airbox and install a nice chrome podfilter
Emgo Tapered Slash Cut Muffler (http://www.northacc.co.nz/content/kernel_public_catalogue_indexViewEntry.aspx?intKer nel_catalogueEntry_PK=885)
Clubman bars
Repaint bodywork in honda red

Pics to come

[gijoe1313]

zomg, where is Xwhathisname-formerly-known-as-Xerxesdaphat! :confused:

[xwhatsit]

Lol -- am I really so well known on here? Not only did you send me a PM but several people pointed me straight to this thread. *sigh* :laugh:

I suppose the first thing to ask is, is it really a CB250RS? You say it's 1985, they were only made til 1984. In 1985 they were replaced by the CBX250RS. I suppose we'll know with photos. Is it a two-into-one exhaust? Either it's not a CB250RS or it'll be an aftermarket exhaust. The 12.5kW issue is unusual too, I have seen reference to it before, but they were not made in very high numbers (the 12.5kW thing in the UK came in pretty much at the end of the CB250RS era) and it seems strange there'd be any here.

Anyway, assuming it's a proper CB250RS:

I *had* a proper CB250RS carb lying around, but it's now fitted to an FXR150. I have another carb too, but it is not in good condition and I suspect it needs an ultrasonic clean to unclog some internal passageways. I'd ask Econohonda first to see how much a good carb would be. Stock carb is a Keihin PD70. One would expect the only restrictions would be in the carb, possibly exhaust too -- don't think they'd bother making a separate cam etc.

The clutch lever perch flogging out is a standard complaint. I've gone through a few cables because of it (it lets the cable rub too much). I'd hacksaw off the existing perch and fit a separate offroad perch in its place. You can get these fairly cheaply, have a look around on Tardme and even motorcycle shops. I'd keep the switchblocks at least, you'll have a headache fussing about with other things.

I haven't taken the airbox off yet permanently, but I tried it once or twice and there were no noticeable flatspots, just a lot of induction noise. If you're fitting an aftermarket exhaust you'll probably want to have a look at jetting anyway.

Watch with clip-ons and clubman bars that they don't foul the tank. I've got a ding in my nice paintwork because of my clip-ons. If you are going with clip-ons, the forks are 33mm. 32.5mm ones are a bitch to get on -- DAMHIK!

Flat battery seemingly did cause me issues, but I might be wrong -- certainly it seemed to be slightly easier to start with a capacitor fitted in place. The cap I've got in mine is 50,000uF (I think), a big blue electrolytic thing I got from Surplustronics for a couple of dollars. When I tried with nothing at all (just connected battery terminals to each other) I had no lights. But it'll run very happy with just a cap, as long as the headlight is always on (slightly higher voltage in the system without a battery to load things down).

When well-sorted they're a piece of piss to start. The biggest issue I had with mine was weak spark. Get a new spark plug (DR8ES-L or DR8ES or DR7EA/DR8EA at a pinch) and make sure you're getting great big fat blue lightning bolts. Might just be old fuel too? At least drain the carb float bowl.

Tyres, I loved Avon Roadrunners, but they don't make them any more. BT45s are good, the 90/90 on the front is wonderful, but the 4.00 I have on the back is disappointing. I'm told TT100s might be good -- I might try one on the back in a 3.50 size if I can get it. Stock is 4.10, very different profile from 4.00. Looks like 3.50 might be a lot closer to 4.10 (about 100/90 as far as I can work out). Problem with 18" rims is the poor selection.

Hope you can get it sorted, they're such a laugh to ride when they're sussed out, so light and narrow and easy to throw around and the engine is a plucky little thing that likes to rev.

[tychver]

YES :D MC02-3001685 Exhaust is a badly made 2-1 custom job done for as little money as possible.

Drained the float bowl and new plug, also topped up the oil, was VERY low :Oops:

Engine runs fine but develops some smoke around 6500rpm. Never did this before, wondering if I've had a partial seizure. The other thing is I topped it up with 15w40 oil, this is way too light. Think it's just getting past the rings? Didn't notice the engine seize at all?

I haven't ridden it hard enough to tell how fast it is and therefore whether it is restricted. Engine number doesn't match the frame, MC02-3001687 and MC02-3001685 is that normal? The carb is a PD70E which I think means it's a UK spec 12.5kw RSC but not a delux version. Also supports it being an 84 bike registered in 85. Rego papers are for Japan import so either the bike never got to the or the engine isn't the original. I've got about 7 years of service history with it.

It's a bit of a shed to be honest.

If the smoke at high revs indicates a partial seizure I'll tear down the motor. Dad used to build aircooled VW performance engines and owned a few Suzuki GT125s and a GT380. Also got an uncle who collects and restores Yamaha TT500s and XT500s.

Thanks for the info about the clutch lever and running battery less. I've got stuff all money at the moment so it'll have to wait a while for anything.

[xwhatsit]

Don't stress about the smoke, see if it clears out with a good thrash first (get the engine nice and hot and cooking). My bike seems to leak a bit of oil every now and again down through the valves into the combustion chamber when left for a while and will smoke for a bit. 15W-40 is fine, make sure it's mineral oil though, synthetic seems to creep past the seals. I use diesel engine oil, Delo 400 if I can get it, it's cheap mineral oil without any friction modifiers which can sometimes cause clutch slippage.

MC02 is the right bike, yep! I wouldn't know about matching engine numbers, I've got a Deluxe electric start frame with a kickstart engine in it.

I did a quick search on CMSNL and found this page: http://www.cmsnl.com/honda-cb250rs-zc-1982-germany-125kw_model16375/partslist/ German 12.5kW model. The only difference in the carb I can see is the part number for the needle jet (what the main jet screws into) is different, but I can't see how that'd drop the power from ~20kW to 12.5kW. Jetting seems to be the same. The same camshaft is specced. Same piston, same cylinder head, same C.D.I., the works.

It is however interesting to note that the part number for the centrifugal spark advance unit which resides next to the clutch is different. I wonder who would know how they were restricted? I suppose that would manifest in it not wanting to rev right to the redline. One should note however that that CMSNL page is for an electric start 12.5kW model, but you wouldn't think they'd change the nature of the restriction. It should manage an indicated 130kph easily enough on the flat, if it can't do that then I'd be scratching my head.

[tychver]

Few pictures of the bike which is now after this last lot of rain far rustier than it was and the bodged 2-1 exhaust and muffler.

[tychver]

http://www.trademe.co.nz/Trade-Me-Motors/Motorbikes/Parts-for-sale/Performance/auction-206245761.htm

GB400/500 Carb. Apparently it's 42mm mikuni though which seems far, far too big for my bike.

I was looking for something modern in the 32-36mm range. Is that sensible?

[xwhatsit]

I wouldn't go over 33mm, they already rev out easily enough with that on it (slide carb). If it was a CV carb then that needs be slightly bigger I suppose as they're less efficient w.r.t. throat size. The stock carb is quite nice as long as you make sure the pumper is working OK.

I've been dying to get a CR33 Keihin smoothbore but that's serious biccies.

If you can get hold of the bits my spare carb lacks (I've seen rebuild kits for around $40 on Tardme) and can give it a good clean of the internal passageways (I asked once on here, people reckoned ultrasonic cleaning is the best and is relatively cheap), then you're welcome to it.

I did have a PM from Roadracingoldfart, I'm not sure if he got hold of you too, but he said that there's simply just a small washer on the intake side. So if you remove that then you're all sweet I suppose. This may have been done already, and PD70E is the appropriate carb... maybe you're already derestricted.

[tychver]

Ah, I'll check that. I was going to take the carb off for a rebuild anyway. It feels like the pump isn't working.

[xwhatsit]

Ah, I'll check that. I was going to take the carb off for a rebuild anyway. It feels like the pump isn't working.
The shaft corrodes. Get a bit of sandpaper and make it nice and smooth again. When you put it back together smear a bit of grease around underneath the rubber gaiter so it won't rust up again. As it's only operated by spring pressure if it's not really easy to move it'll just stay stuck there.

[tychver]

Oh, cool, I'll try that.

The bikes been out around the block today, still getting plenty of oil in the mix above 6000 revs but it's running fine. Throttle response is nonexistent, getting nothing from the pump eh, other than that it's ok. I'm still idling about 1600rpm though, if I drop any lower than that it stalls, I'm guessing the mix is completely wrong or the idle jet is blocked.

I'm looking at that cycleworks exhaust on trademe. Were you after it? I'll get it if you're not!

[tychver]

http://translate.google.co.nz/translate?u=http%3A%2F%2Fsteed2-4.com%2Fmy_bike.html&sl=ja&tl=en&hl=en&ie=UTF-8

This guy has:
NSR250 front disc and caliper
FTR Rear drum?
XR350 Piston on custom conrod
PJ36 Carb
Raised Compression
High spec cams
Fully balanced with a 10,500RPM redline
Custom rearsets

I'm damn interested in the rearsets and brakes. Probably going to be the first things to do after the exahust. Know any sources for better rearsets other than GB250 or customs?

PJ36 carb seems huge but he's probably the insane side of 35hp. I'm not so keen on the exhaust though.

I want the SRX600 powered TZ250. That's gotta be FUN.

[xwhatsit]

Sorry bro I better buy that pipe quick :laugh: In fact I just hit the buy now. Sorry :D

Does sound like the carb needs a good strip and rebuild. Stock jet is 122, needle at the 2nd leanest position. 1500rpm is supposed proper idle. The intake manifold tends to get pretty nasty as well which makes it gutless and idle horribly esp. when hot, make sure there's no leaks and fit a new rubber O-ring as the original will be hard and flat.

Oh that guy! That was posted up earlier in the thread about fitting XT350 piston. It looks lovely, doesn't it -- at least in the sense of `going' rather than actually looking (agree about pipe, gah). I'm interested in going `backwards', to a 2LS drum brake for the front. No issues with the rear, put some new shoes in it and it's got lovely feel and more than enough power to lock the wheel. The front disc is horrible I must admit, especially in wet weather (lag much!).

I'd love to know about rearsets too. I've currently got pretty low bars if you've seen a pic, and my feet are further forward than I'd like (on long straight roads when riding for many hours I put my feet back on the pillion pegs :laugh:). Ground clearance isn't too bad but pegs are first to touch. Did you hear GB250 fits? I wouldn't thought it'd be any further back tbh?

I've seen custom rearsets on Yahoo Japan (Japanese equivalent of Tardme). You can buy from there with Okshon.com but there's fees they tack on and shipping can be nasty. Might be cheaper to try and make your own?

[tychver]

I'm currently wondering exactly how much work/money to put into this bike.

Route 1: Fully restored monster RS (aiming for 30hp minimum)

Route 2: Nice looking but internally standard RS. Buy 2 stroke or 400 for going fast

[tychver]

Do GB500 rearsets fit?
http://cgi.ebay.com/ebaymotors/Honda-GB500-Foot-Control-Assembly-Footpegs-GB-500_W0QQcmdZViewItemQQ_trksidZp3286Q2em63Q2el1177Q QhashZitem170307575196QQitemZ170307575196QQptZMoto rcyclesQ5fPartsQ5fAccessories

Doesn't look much like they would?

[xwhatsit]

No, that's a very different setup from how the RS pegs attach. The footpeg bracket on the RS attaches by the swingarm pivot bolt running through the bracket. That has three small bolts around the circumference. And at the end of the day they're still about the same position as the RS pegs, maybe a cm or two different.

Personally I made up my mind long ago to hang onto my RS and never sell it -- therefore any stupid time and money I spend on the thing I don't have to worry about `overcapitilisation' and `return on investment'... all the effort I put into it is just for my own pleasure. However the sensible thing would be just to tidy it up and buy a VFR400 :D

[tychver]

So you're still running the standard rearsets?

Mine don't suit me, even worse once I get some clubman bars or clip ons.

I'm going to have a look at having some simple ones machined out of of a plate of aluminium, relocating the gear selector and rear brake pedal is going to be a bitch though.

How related are the CL250S and the CB250RS? They look pretty similar.

Just been checking Yahoo Japan out. Saw some FCR35s being sold for CB250rs? 35mm seems a bit big but maybe they work!

[xwhatsit]

Yep still standard pegs. Making one yourself wouldn't be completely ridiculous I suppose, the plate is fairly simple. Mind the drum brake actuation rod though, you could always chop it off and use a die to carve some more thread on it. Making a longer linkage for the gear shifter would be a piece of piss with some threaded rod.

CL250S and CB250RS same thing really, I don't think many came to NZ (at least through official channels?). Might even be same frame, dunno, but basically another in the line of the original XL250S family. The high pipes are so cool :D

[tychver]

I've actually found that you can get universal rearsets that you get just mounting brackets made up for and adapt the gear selector/brake linkage. Cheaper than getting own plates made I think. The standard ones are kinda uncomfortable for me even with the standard bars, I'm only 5'8 with incredibly short legs. Kinda like an orangutan.

How close is the CB250N frame to the RS? Looks almost the same, but I guess a lot of those Honda 250-350(60?) frames are pretty similar. The rearsets look to mount in the same palces on those bikes, and aftermarket rearsets are available for them.

http://img.yezzz.com/zm4207942.jpeg

The entire rearset seems to sit higher to clear the exhaust though. Dunno if the peg position is any different to the RS, or even if they will fit and not look stupid.

Custom mounted universals it is for me I think. Damn being short sucks. I can't even get my feet down on my uncles XR650L!

[tychver]

http://www.trademe.co.nz/Trade-Me-Motors/Motorbikes/Motorbikes/Classic-vintage/auction-206566396.htm

CB400Four for 1500 anyone? Just look at those headers!

[tychver]

Engine is coming out of the frame tomorrow. Along with the tank and seat unit coming off. Better put a tarp over it to keep the electrics dry.

[xwhatsit]

Blimey! Fiddling with the engine or painting the frame?

I did it on my own (out and back in again) by dropping the bike on its side and pulling the mounts out, was easy like that, although it's not a heavy engine anyway.

[tychver]

Both :D

I'm reconditioning the engine. Emailed econohonda about getting a complete XR250 engine and gearbox. If it's not ridiculous money, I might grab it and get a sorted RS head on it. Otherwise it's just a new topend, including the damn leaky rocker cover gaskets lol.

I played around in DynoSim setting up a standard CB250RS and playing with it. A simulated curve looks worse than the bike feels. I'm thinking of raising the compression while I have the engine apart. It'll be ok if I just increase the valve clearances by however many thous I have taken off the deck right?

I'm wondering if I can get anything close to 10.5:1 without taking too much. Maybe an XL/XR wiseco is just going to be easier.

It's also getting a new coat of black on the frame, honda red on the body panels, relocated/smaller battery and a nice chrome filter.

[xwhatsit]

I'm going down the 335cc big-bore route, but it's not straightforward and I'll have my existing engine to fall back on if it blows up.

You can take the standard engine out to about 270cc using the standard cases (i.e. you don't have to machine out the crankcase). They were pretty popular mod with the XR250 back in the day I think, there were possibly a few companies who made kits.

I reckon Wiseco might be smarter than shaving the head. Wiseco do a 10:1 for the pre-RFVC 250s, +2mm oversize too, that would put you at 262.2cc instead of stock 248.6cc. If you wanted to shave it I don't think you'd get so far as needing to fiddle with the valves (remembering if you have to add too much slack to the valves, the rockers wear faster and you'll get less opening as well, so that will hamper performance). The stock piston has little cut-outs for valves, you could just machine a little bit more with a dremel until the valves clear it, allowing for a bit of rod stretch.

My RS will ping at low RPM with a stock piston (what are they, 9.3:1 or something?) and 91 octane. So be careful lol.

The later electric starts had more compression in the official literature but Honda never changed the horsepower/torque figures with it though.

I reckon Wiseco 10:1, +2mm (you'll need to give it a rebore anyway) and you'll be laughing. 9.3:1 to 10:1 is pretty good.

Who ever heard anything about hot cams? They must've made a fancy cam for the XR250s, surely. Then again the CB250RS cam is better than an XR250 or XL250 cam anyway.

[tychver]

That's interesting. Mine doesn't ping at all, although it's running stupidly rich.

The rocker covers are leaking bad, and the outer oil seal on the headgasket is going (who knows how long before the inner?), so I figured it was better to save my self some expense in the long run and do it properly.

Option A: Gearbox is in decent condition and it's just an oil seal. Bore is fine, drop in new piston and rings.

Option B: Gearbox is in decent condition and it's just an oil seal. Needs rebore. Go for wiseco and have engine rebalanced plus a hot cam and new valve springs. 28-30hp.

Option C: Gearbox is fucked. XR engine and 6 speed box from econohonda. CB250RS topend with a wiseco 10:1. FCR35. Could get a couple of extra HP by going for a more agressive cam and revving the tits off it.

Oh dear.

[xwhatsit]

The rocker covers as in the two little silver valve inspection covers? Just an O-ring on each, easy -- but if you're talking about the rocker cover as in the whole valve cover on top of the cylinder head, this one is a bit of a tricky one.

There's no gasket, and I don't think you can really add one as the cam runs directly in the head/rocker cover, so you'll change the cam bearing clearances which can't be good. I've wondered about machining out the valve cover and adding a rubber O-ring type thing that sits in a groove? Might be tricky. It needs a gasket because the cheap aluminium warps and you'll be lucky if some bastard hasn't nicked the surface.

The real problem though is that the rockers themselves wear out a little sealing O-ring on their shaft (see what looks like two screw heads on the outside of the rocker cover) and leak out of there... a prick to get access to, the retaining pins seize in there, not looking forward to it.

Making the top-end oil-tight is not easy, heh.

I'd love to discover one of these aggressive cams. I should ask Malcolm at Econohonda if he has anything lying around :)

[tychver]

http://www.megacyclecams.com/catalog/pages/page%2025.pdf

http://www.xlintperformance.com/performanceparts.htm

Those are both for XR/XL engines so probably different grinds to the CB250RS but it looked to me like their first cam was pretty much the same as a CB250RS cam.

Standard CB250RS timing is 5/30 and 35/5. Not sure about the lift.

The first megacycle cam is 4/32 and 35/8 so it has a little longer duration with slightly more overlap. Overlap reduces effective compression so engine manufacturers tend to avoid it.

If I end up going to XR engine route I'm going to get a cam ground by kelford and clean up the head my self. I've got a dremel and a flexible shaft and experience ruining VW aircooled heads :headbang:

Did the megacycle exhaust improve your performance at all? I'm debating whether to get a custom system made up or just clean up this one with a proper silencer.

[xwhatsit]

Thanks for the link there -- interesting stuff! Needle-bearing billet cam? That's a great idea considering the plain bearings which are often shagged.

Can't imagine the 134-50 grind being particularly docile >_<

It's a Cycleworks zorst (they still make and sell them new -- maybe $300-400 or something?). It's improved mid-range torque to the point where you can short-shift it and make nice progress, but it's lost some top-end. May be just a jetting thing; all I've done is pull the plug to check it's not dangerously lean. I'm not going to be too fussed fiddling about with the carb as I'll need to start from square 1 with the 336cc engine.

[jester_parks]

got a "hot-cam" in the shelf waiting for the big engine.
Can`t say anything about the timing yet, but it is obviously a regrind done for (the identical) XL-engine and gives more lift.
Got it a while ago and will take the timing as soon as its in the head

[tychver]

I'm attempting to buy a parts CB250RS in Dunedin. It's pretty rough but the exhausts are still there and the bodywork is completely straight and not cracked like mine. Not sure about fork corrosion, haven't checked. Still
+1 for straight tank.

Apparently it's a non-starter though, possible electrical fault, although the owners swears me blind it'll just need a battery.

I've decided to just get this bike put together and running, in a nice but mostly standard configuration. It'll be as close to factory condition as I can get it without spending large amounts of money I won't be able to get back.

[xwhatsit]

Unless I'm missing the obvious and it's an electric start model (so he just can't turn it over) CB250RS's will start just fine even with a dead-flat battery. They'll run fine even if you just connect the positive lead to the negative lead and leave the battery out altogether -- however you won't have any lights. Might be a good thing to try before buying it.

I've got some red side-covers... can't fully recall condition, they're buried with a whole bunch of crap. I think they're decent enough though. I'll flog them on very cheap if you want them (like $10 each); I'd give them away but I need some money for a new camchain, gaskets etc. (doing up another stock 250 engine, my gearbox is getting worse and worse -- I've got a bottom end and a top end but they need to be joined together :laugh:). There's a red tail/seat too... the tank is pretty farked though.

There's some good forks too but I'm considering hanging onto those to keep a complete rolling chassis for bucket racing or something.

Let me know if you need bits and bobs, chances are I have it and might be persuaded to get rid of it.

[tychver]

I might take you up on those side panels if I don't get this parts bike.

I'm pretty keen on it though, because there's a whole shitload of little things I want. Brake reservoir, side panels, tank, possibly some gearbox bits, the unrestricted cab and intake, exhaust system etc.

I feel like a kid in a candy shop just looking at the pictures. It's seat is fucked though, and the plates are dead so I don't really know who would want it apart from a person already with a CB250RS.

[tychver]

Well, I won that CB250RS parts bike auction. The owner lives 300m away from me! I'm picking it up thursday night, hopefully I can have mine running and WOFed on Sunday. I need to drain the synthetic I put in and get some decent oil in there, degrease the entire engine and find the leak (if any).

I'll then start stripping the clean bodywork off the parts bike and repainting it in a nice coat of modern honda red. I'm thinking of a silver honda wing on the tank, and CB250RS on the side panels in black, but with the "RS" in blue.

Starting to think about the engine...

If any work needs doing internally I'm going to spring for the wiseco and have the entire engine rebalanced. I'll get the cams reground at kelford to something like the Megacycle specs and do a light port and polish on the heads my self.

Should end up with 30-35hp, a fat spread of torque, smoother engine and several years of good riding for $500.

[xwhatsit]

Nice! If you want to get some Honda wings made up cheaply, send a PM to MSTRS. He does all sorts of vinyl cutting, could do the `CB250RS' lettering too. I got some 1960s style ones instead, they look quite neat I reckon, but I'm sure he'll have designs for the more modern ones too.

In terms of rebalancing, what's the story there? When I was first mooting the idea of a 350 piston I asked about this, I got told because it's a single, you can balance the crankshaft weights as perfectly as possible but you won't achieve anything, only shifting the vibrations around 90 degrees (I think that was the figure). Hence the need for the balance shafts.

The Wiseco piston won't be substantially different in weight... maybe you could just leave the crank alone?

[tychver]

Hey, thanks for the tip about the wings, but I've gotta strip, sand, seal and and fill the new tank first.

Well yeah a single can never really be balanced all that well due the fact that the conrod has a greater movement mid-BDC-mid than mid-TDC-mid.

But making sure the balancers aren't adding any undue virbrations themselves and that the crank is actually balancing the vertical momentum of the piston can go a long way to making a single run smooth.

[tychver]

My second rusty piece of shit. Note the much better side panels and tank and exhausts without holes? :D

I've yet to start it, it needs a new fuel line and a bit of electrical work. If the engine is in better shape I might drop it and fit it to the my bike, which is already road registered, unlike this one!

[tychver]

Pic of my new beastie:

[tychver]

Bodywork and exhausts came off the whore bike last night.

Dad's teaching me to strip and fill. There's a couple of small dents in the nicer which are getting smoothed over.

I'm also going to brillopad the exhausts.

[tychver]

I'm measuring up for some CB250N comstar mags. Still can't decide whether to use the CB250N 270mm disc. It's a fair bit bigger than the little 243mm POS on the RS. Caliper is probably better too, and the headlight would look nice.

Bah, this is turning into the entire front end :|

[tychver]

Oh gawd.

Now I want to build a CB400 four RC160 replica.

[xwhatsit]

I'm measuring up for some CB250N comstar mags. Still can't decide whether to use the CB250N 270mm disc. It's a fair bit bigger than the little 243mm POS on the RS. Caliper is probably better too, and the headlight would look nice.

Bah, this is turning into the entire front end :|
The CB250/400N has a 19" front wheel so that might be tricky. Interesting that the later Japanese 250RS had a two-pot calliper. Nissin I think... would be better than the original `no-name' (i.e. Honda) one-pot calliper. The later electric start models you see in NZ and the UK only had a one-pot calliper, so maybe it was the final Japanese domestic model that had this fitted (they did a CB250RS-R, red and white livery, gold forks and rims etc.).

Oh gawd.

Now I want to build a CB400 four RC160 replica.
I like the later Honda 250cc race models, much sleeker tank/seat combo. Although the RC160 is a special bike for being the first 250cc four since the pre-war supercharged bikes, and Hondas first four I think? The CB400 four is a gorgeous bike though on its own -- you mean the CB400F, 70s model?

[tychver]

Measured up the CB250N wheels. Which turned out to be Nighthawk wheels. 18" front 16" rear.

However I might be able to pinch the drilled disc :D

Changed the oil and cleaned the strainer yesterday. Don't know why I did it on such a windy day, trying to catch the oil was a bit of a laugh. Put some of that oil cleaner stuff in it before I drained it. Dunno if it got much out but it seemed pretty sludgy. Filter screen seemed fairly clean though, so I guess it's just a lack of the oil being changed for like 9 months. It's done all of 8km in that time though...

Started removing the carb from my parts bike today. It's completely missing the choke cable assembly. Ah well, I've got one on the other carb. Also discovered that it's not siezed. Merely stuck in gear. Maybe the barrel is in better condition than mine? Hmm, need to get that off.

Did some more cleaning rust off the exhausts. Tis fun.

Brakes are on the list next. Stealing the reservoir from the parts bike as it's much less warped. Leaver is in fine condition on mine so I'll keep that. Not sure what to do about that back brake. Seems pretty fucked. It's not returning properly at all and is sticking on. The one on my parts bike is much better, and with less wear on the shoes. Maybe I should swap it over. Hmm. Sounds harder.

[tychver]

Saturday:
Finish cleaning up the headers; the interior welds are horrible
Get the rest of the rust off the mufflers
Drill out the rivets and gut them
Dismatle the carb after it gets dark

Sunday:
Drain brake fluid and swap the reservoirs over. Flush through and refill with nice new Ferodo DOT4 fuild (came in conveniently motorbike sized bottles). Hope it doesn't eat my brakes. Ah well. I've got 3 sets of front brakes handy.

[tychver]

Exhausts got done. Sounds fantastic, runs much better. Pulls strong from 3k to 7k. Not sure what's happened to the top end, maybe I've still got the restrictor plate in there? I'll check when I rebuild this carb.

Never got around to rebuilding the 2nd carb as I've decided to throw it away and get a VM34 for my more highly strung bike. It's fairly seized so I'm definitely going the performance rebuild route.

[xwhatsit]

Yeah I get the same thing with that more open Cycleworks pipe -- pulls strong midrange, but the top end tails off.

I just snaffled the XR250 cylinder head that popped up on Tardme. Bargain -- $70, no cracks, that's a rarity. So I'm going to rebuild the other bottom end I've got into a nice-running reliable standard 250 engine, then get to work on my current engine to bore out to 336cc (piston arrived a few days ago), as it's shagged anyway and needs to be opened right up and split the cases (first gear in the gearbox is toast).

I so nearly bought a VM33 out of Japan a while back but the bidding got too high. It was a Yoshimura-badged thing -- apparently the VM33 is completely different from the rest of the VM28, 34 etc. series. Yoshimura collaborated with Mikuni to make this VM33 pre-jetted for the CB250RS. They made different sizes for other bikes too. At least this is what the auction said (I think, translating from Japanese). Only problem is the VM series don't have an accelerator pump, so you can't snap open the throttle like you can with the PD70A. I'm more keen on a Keihin CR33 (again, sold pre-jetted for CB250RS in Japan), don't know how the prices compare though. Might have to go a little bigger with 336cc.

[tychver]

Depends on how much power you want to put out. CR33mm smoothbores are generally considered to close to their limit on 1000cc inline fours from the 80s putting out 120ish hp, so I guess they're not going to be good for much above 30hp on a single. Infact they might even be worse because of the giant pulsing effect of singles. I'd go with the 35. Big is good right?

I'm going for the VM34s for $250 on my rebalanced wiseco 6 speed screamer :D

[tychver]

Carb rebuild kit arrived today. All looks in order, although I haven't compared it to what's actually in the carb yet. The weather is too horrible to go out and get it off the bike.

[tychver]

Got new bars. Cheapo ones off tardme. They'll do for a rat bike.

Also bidding on a VM34 on trademe.

[xwhatsit]

Nice, what sort of bars?

VM34... that's the top-pull version, right? No throttle `spindle'. You'll have to get a new cable made up. I'd like to see what you end up doing, there's a lot of those old-style roundslides around... you were right, I'll need a bigger carb with 350cc, and finding an XR500 carb is a little harder than I thought.

[tychver]

Yeah top pull old style roundslide. The throttle spindle is missing from the carb on my parts engine.

Current plan is to get the second engine running and move it onto the bike, but I didn't want to get stuck without a working carb so I bought a VM34 for $80.

Once I've got it all sorted, I'll put the rebuilt PD70 back on the newly rebuilt engine.

The stanard style exhausts are more restrictive than the standard carbs so there's not much point going bigger until I get my cycleworks.

[tychver]

Rebuilt the carb today. Couple of problems:

1) Someone has stripped the heads on one of the screws holding the throttle arm to the slide. Meant dismantling my second carb to get the one out of that. this turned out to kind of be a blessing because...

2) One threads for the float bowl screws broke as I was tightening it up. This meant moving all the nice stuff into the other carb body :(

Runs a treat now though, no refusing to idle and plenty strong up top. Needle in old carb was very worn, and the main jet was gunked up. No wonder it didn't idle properly and felt lean up top.

Not running the airbox at the moment, I'm planning to run with a pod and the battery (and all other electronics down there) under the seat.

[tychver]

Decided to ditch the airbox permanently and run a pod. Will rejet when I put the cycleworks exhaust on.

Still haven't done the bars and controls. Picked up a bit of a chest infection (hopefully not swine flu lol) which necessitates 6 cups of tea per hour when working outside.

I'm going to keep the standard seat minus the rails. Can't be fucked with messing around with the hassle of making a new seat unit.

Switching to a dual rectangle headlight and KOSO XR-SR digital dash is very tempting. Not sure I can justify the $450 :shit: though!

I might put off upgrading the headlight till I'm on my restricted license and can ride at night eh.

Pictures once I get the bars on.

[tychver]

CB250N front end and wheel conversion is officially beginning.

It's been spurred on by my completely fucked master cylinder. And my second completely fucked master cylinder.

If the reservoir screws strip their heads. Don't try to drill them out. It's impossible to do cleanly lol.

[murdercycle]

Sorry to bump this old thread but it seems like the place to ask-
I've got an 85 CB250RS, and fuel leaks from the carb when you put throttle on. I think it's an accelerator pump, but I went to honda to get a rebuild kit and they couldn't help, where are you guys getting them from? Is it worth it to just replace the carb with a "hotter" one? I'm 105 kilos so any more power is welcome lol.