Slightly Cafe CB250RS Project

**tychver** · 1st March 2009, 20:32

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
Clubman bars
Repaint bodywork in honda red

Pics to come

**gijoe1313** · 1st March 2009, 21:30

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

**xwhatsit** · 1st March 2009, 21:51

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*

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** · 2nd March 2009, 18:21

YES

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

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** · 2nd March 2009, 21:41

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-z...375/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** · 3rd March 2009, 19:28

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** · 6th March 2009, 18:20

http://www.trademe.co.nz/Trade-Me-Mo...-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** · 6th March 2009, 21:16

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** · 6th March 2009, 22:58

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** · 6th March 2009, 23:23

Originally Posted by 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.

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** · 7th March 2009, 13:39

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** · 7th March 2009, 13:46

http://translate.google.co.nz/transl...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** · 7th March 2009, 22:19

Sorry bro I better buy that pipe quick

In fact I just hit the buy now. Sorry

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

). 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** · 8th March 2009, 08:28

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