Honda CB250K something - very very long term project...

[pdg]

[A100man]

[pdg]

[lingeringstin...]

Trust me, you don't want a "vintage" Honda engine unless you like spending money.

Other than the head that looks near as dammit to an old Benly engine, which is what the Chinese clone now for a zillion different things. so I'd bet there's a lot of new bits from different engines that would fit. That was probably 6v and points but they're easily made 12v and electronic ignition.

A while back I cobbled a five speed gearbox and electronic ignition into an old CD200 and tried to flog it. None of the old duffers looking for "vintage" CD200 engines parts would touch it because I'd modernised it and eventually it made a very nice little go kart engine for somebody.

I made a 202-ish cc engine by having a Honda 250 barrel cut down to the same height as a 125 barrel and bored out to something like 56mm and stuck that on a Benly 125 bottom end with a 233 gearbox and uprated clutch in it. Went like stink, much better than a 250. It didn't cost much to do that. Biggest expense was having the barrel sawed off shorter, the rest was piss easy and it would bolt straight into any Honda that used a 125 twin. Somebody has it in a CB125t right now and it's fast as fuck for what looks like a 125.

I'm running some concoction of Honda/Chinky parts cobbled together and it works great. If you want to have a cool "old bike" that's reliable then just put a modern engine in your frame.

[stinkwheel]

The K-series CB250s are actually pretty nippy. 100mph bikes.

The CB series underwent a steady progression of detuning and increased fartiness from then on.

They have a 180 degree crank rather than a 360 degree which I believe the CD series have.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[pdg]

In a way, putting a modern engine in an old frame kind of negates the point - at least for me, on this one (it also negatively affects the mot and tax status if you play by the rules). If it was purely the look then 'factory retro' is now a thing, along with 'factory cafe racer' and 'factory flat tracker' and 'factory streetfighter' and (shudder) 'factory custom'.

Modifying to electronic ignition would be fine, but I honestly don't think the benefits would outweigh the hassle. With a 360° (or 0° if you prefer) crank twin then yeah, bung in a pickup and run a twin output coil with full wasted spark and off you go - with a 180° crank that runs cylinder specific double points with a pair of single coils it gets that bit more involved.

I put EI in my '72 land rover purely because of cost - the distributor was worn out and an electronic version brand new was significantly cheaper - if I could've sourced a new mech distributor for the same price it'd still be on points.

The unreliability of these older engines is almost always down to laziness of maintenance - things like said points require relatively frequent adjustments to keep things running right - bear in mind that the relative reliability of 'vintage' honda (and other Japanese marques) when they were new was a significant factor in the death of the British motorcycle industry.

As to the voltage of the electrical system, the CB runs 12v anyway - but my XL is a 6v system - I see no reason to change it. Other than the ability to run EI (which again, I'm not intending to do) there's really no other significant differences apart from the headlight bulb and as it's unlikely to be ridden much at night... It doesn't use the battery to power the stock ignition and it's kickstart only. 12v is only 'better' than 6v if something you desire isn't supported on 6.


I still don't understand why it appears to be considered expensive to have an old bike like these...
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Any and all advice given should not be followed - if you have to ask it means you don't know so get a man in to do it for you.

[Easy-X]

I've often considered taking an unloved '80s bike, e.g. 250 superdream, and retro fitting EFI. No idea why... I'm just not right in the head.
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[pdg]

[lingeringstin...]

In my experience the only bad thing with old bikes is when the the parts aren't easy to get any more and all the spares left are just junk that gets called "vintage" and the price of goes up astronomically.

I'm fine with points but I like as much light as possible which is why I've got a 12v Jeep LED headlight on a 40 year old bike. My bike's so old it doesn't have to have indicators but I have them anyway. I don't have (or need) a front brake light switch but my rear one is from a Jag so they're robust and easy to get. Most of what my bike is made out of is actually sensible and works as opposed to being "vintage" just for the sake of it.

Personally I would never have a modern bike because they look like soulless cack but I don't see any problem with cobbling things together out of bits you like. I'd be perfectly happy putting one of my oddball modified engines in an old Honda frame and ignore the purists who have to repeatedly inform me that I've ruined a classic bike by putting something non-standard on it. If I like it then it's not "ruined".

To me bikes are for riding, not some kind of three dimensional jigsaw puzzle that has to go together absolutely correctly. I hate snooty vintage nerds who know exactly which transfer was the correct one for the battery box of that particular year.

I met a Vincent dude once that modified his bike to take an electric starter. Good on him. Made the purists cry I'm sure.

[lingeringstin...]

[quote="stinkwheel"]The K-series CB250s are actually pretty nippy. 100mph bikes.

The CB series underwent a steady progression of detuning and increased fartiness from then on.

They have a 180 degree crank rather than a 360 degree which I believe the CD series have.[/quote]


Yeah, I once had a "vintage" CB750 that was good for something like 90mph on a good day. I've had nippier 250's.

The Chinky clones of the Benly engines that I've come across are 180 cranks for the 125 and 360 cranks for the 250's. Fuck knows why. I've run both in my cobbled-up engines with the same carbs and found not much difference really. Best one was a 125 crank using shortened 250 barrels.

[pdg]

[stinkwheel]

If I might make a suggestion? Instead of a "cafe racer", make a "racer".

Pared down to bare minimum with clip-ons, single seat unit, coffin tank and Rickman style fairing. As I remember, you could rearset them quite easily by fabricating a footpeg mount plate and flipping the gearshift 180 degrees (also race-shift).

Honda racing colours, red tank and seat unit, silver fairing with a yellow stripe, yellow or green race number backing.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[pdg]

[stinkwheel]

Lots of fibreglass rickman replicas out there. I've used this company before and their layups are pretty good. You need to go via one of their UK dealers unless your French is very good, they refuse to deal in anything other than French and will deliberately misunderstand if your grammar/gender etc isn't perfect.
https://www.poly26.com/norton-rickman-replica/4598-tete-de-fourche-rickman-replica.html
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.