Project Honda CB250RSD Project

Thanks all for your comments, pointers and food for thought.

now CMSNL used to be only a few kms away from my home in NL, and I have occasionally ordered bits from them. Expensive but if needed, fine. But you need to know exactly what you need and why. In this case I'm dealing with what seems like a carb that needs more TLC. I've already had it apart and in the ultrasound cleaner, float valve is new (not OEM). Replacing all bits at the full price is not really an option, my pockets aren't that deep. Also many after market suppliers seem to be unaware that there are two carb types used on bikes called "CB250 RS" and getting the right stuff for the non-vacuum type is not so simple. If I knew the bike would be perfect after spending on the carb that would be OK, but this is just the road forward to the next job of course. Maybe I should go gardening but there the weeds keep comingback as well, only solution

And nice to know : the shaped rubber seal of the float bowl was OEM (bought from dealer, NOS), just didn't like modern petrol it seems.....

However, current problem is probably a damaged float valve seat or dirt in there. I'll take it apart once more I think. The hunt is on for a known good carb at less than the cost of say a new thingie for the accelerator pump, which together with a a few O-rings for the carb, after taxes and postage, would cost more than I paid for the whole bike to start with (actually, lots if it came in boxes but never mind)

About removing excess sealant, I'm not worried about oil passages inside, no sealant there. The possible problem is pulling out the sealant to the outside in a few places where there is only a very narrow seal, like near the bolt hole I have drilled out to accept an M8 bolt to replace the original M6. I'just let it be for now, or perhaps paint it black so it won't be seen

cheers, Frans

 

Nah, EU standard RON 95 petrol can contain up to 5% alcohols, and I never use the 10% stuff. Ethanol free is available if you know where to get it and what to look for, but it is rare and expensive. And no viton available for this carb AFAIK.

 

As I'm sure you've all been waiting for an update, here goes : I've bought another carb in July, took a holiday and had a shoulder misbehave. By the time I could do work on any bike I had to fit heating in the new garage first. While literally looking down on the CX500 during that work noticed a funny bit sticking out of the fairing. On investigation it turned out to be an broken exhaust stud, yes, break just inside the cylinder head of course. As a bonus the tax regulations here are set up so I cannot use the bikes in December/January/February, great, end of biking this year.

So on the last day of November did a quick carb change on the CB250RS and hey, it runs ! Still work te be done, power is coming in with some hesitation through the revs but it still managed 100+ km/h. Pretty good I'd say, only took a year and bit to do, lots of money but no need for pedals now

To be continued next year, the 250RS now laid up for winter and work on the lame CX big brother.

 

As you may have noticed it is now next year, and the threat was not empty, I'm back working on the CB250 RS.

Last attempt to get it running was a fresh carb before the winter stop, so put fresh air in the tires and took it out for a little tour last week. Got it going - just about more about that later - using the e-starter. Seemed to run well at lower speeds - very pleasant bike. Around 90 kmh and above (say 60mph) it didn't really want to go, felt like fuel starvation. So far so good. Just to make sure it wasn't a CDI ignition problem I checked timing using the strobe, fine. Swapped in the spare CDI unit to see if that would make a difference.

Now maybe I shouldn't have done that. Refused to start no matter what I tried. Which is a nuisance when all you've got is a small battery and a electric starter turning the engine just once past the first compression stroke before disengaging.

Finally fed up with this e-starter - always gets lousy reviews - I thought I'd tackle that first. Old newspaper cuttings say some people reverted to fitting kickstarter but that is beyond the pale of course, if I want to kick a bike I just kick it, period. Took the thing apart, didn't see anything very wrong. Put it all back, no change. Apart again, look, study, read the FSM, look at part listings different from actual bike, curse. Decided Honda didn't get this weird electric latch right, that is the coil and levers magic appearently supposed to keep the starter engaged as long as you press the button, which it obviously did not. Put things back on the bike but with shims inserted under the outer cover so I could just see it working. That's after days of fiddling. Guess what? The latch indeed didn't work. Not completely unreasonble given that the relay driving it -this blue rusty thingie



pictured here next to the replacement from the odd bits box - was clicking nicely but not really switching power to the latch coil.

I don't understand Just why they use a relay here, it is simply driven by the power for the starter and all it does is switch on the 12V for the latch coil. Might as well have connected it directly? Anyway, the starter now seems to work, keeps on cranking untill the battery gives up - that is soon. Oh well, only took a couple of days to find. Fine bike workers like me cannot be expected to check all the basics like electric power actually arriving, right?

Even sparks seems to be present, maybe I really should check a few more basics like compression and such silly stuff...

To be continued (this year)

 

@Murdo : Had another look at the circuit but it seems the relay is simply active as long as I press the starter button? Should the engine decide to run then the freewheel/starter clutch should let it run free ? I did check that clutch and it does run free in the desired direction. Anyway, one sunny day I'll worry a bit more about that, it works now, battery on the charger, more later

 

Succes at last, it runs ! Not only that, it even runs very nicely thank you. It doesn't even leak oil anywhere, the cylinderhead stays nice and dry. Wow!

The last steps were another battery - last one died of neglect really but they're cheap- and giving the carb a nice ultrasound clean. Even then it wouldn't run untill finally the penny dropped and I checked the float level - ah, petrol in carb bowl some 10+ mm low. Fixed that and now it behaves really well. Motorway top about 120 kmh, seems normal to me given my size and weight (both not neglegible ) Here a last picture, one blue CB250 RS in the sun :



scratch that, it is in the shadow really, never mind.

If there is one thing this little machine did it is reminding me that you should really not neglect checking the basics. A relay may click very nicely, but that doesn't mean it works well, not really. The carb may be clean and shiny, doesn't mean the bike will start. Honest, when was the last time you checked float level properly using a bit of clear tubing? And other funnies like that, to be expected really on a bike costing 150 euro, partly dismantled.... The blessing of all unknown previous owners included.

But hey, it took only a year or so but a pleasing result, who cares how.

Next thing to decide is, well, what next. There is at least one bike in parts waiting in the garage. There's another basket case waiting, rusty CX stored under a tarpaulin outside for many years, came with 'new' tyre - dot stamp for 1990....
May even have to sell this little one to refill the biking pot but first ride it for a bit, don't know. I'm kind of used to see it standing around, the garage would look empty.

Anyway, end of project, summer, let's go biking !

 

Next has been decided.......

The bike ran well and I could do with the money and the space, got an offer almost covering the (high) cost, and - yes sorry guys - sold it.

Now I no longer own a 250, just a couple of 500's, I guess I'll have to leave you for now. However, if a nice (cheap) 250 four happened to pass my garage I might be back Not likely, they're rather rare here in the EU and not cheap if ever you see one.

Anyway, nice knowing you, I did need some encouragement !

Keep the shiny side up and the black round things on the road,

Frans