Keihin Carb CB 250 Honda RS

[St George]

When I dragged this shed find home it had sat since 2005. Fresh petrol and it started and ran nice.. After a few weeks replacing brakes, tyres etc it is nearly ready for an MOT. Would it start NO. Dry plug, typical blocked carb. Tried carb cleaner in the intake and it fired for a while.
I have stripped and worked on Amal's and Dellortos over the years but this complex looking Keihin PD is unknown to me.
I am used to main and primary jets and primary circuit drillings. I don't know anything about the cover that has three screws on it, is there a diaphragm in there that needs changing. I have aerosol of carb cleaner and will strip it tomorrow armed with all the tips you lads can give me.
Love this forum. Thanks.

[virus]

its unlikley to be anything in the slide area thats causing it, Given how simple it is to take off and back on, I'd take the bowl off, jets out to clean including taking the float valve seat out and making sure thats clean then re assemble and it'l no doubt run again.
____________________
own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[Meatybeaty]

[Meatybeaty]

Sorry matey need me glasses on, 1981

[St George]

Thanks for diagram, nothing like that. That looks like a twin cylinder type carb. Mine was registered Jan 1982. Single Cylinder > Thanks

[Meatybeaty]

This one?

[virus]

its this one. same as the xl250 and xl500

https://www.dansmc.com/carbs/Japanese_Carbs/Keihin_HonXR_XL250_500.jpg

Remove everything in the the float bowl, clean it and put it back in. do not fuck with the accelerator pump linkage unless you absolutely have to, they are a fiddly bastard to put back together without loosing the spring or tearing the probably worn out old diaphram.


Cheers
John
____________________
own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[St George]

Virus, that is the baby. Just found a Youtube rebuild on that one, soaking the body overnight in brake cleaner. Not as bad as they look SO FAR

[virus]

I think my 250rs is the only bike I regret getting rid of, so easy to work on and fun to throw around.
____________________
own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[St George]

Is the mixture screw number 16, they are normally on the outside of the body. Thank you.

[St George]

Virus, mine is the same as the red one on Ebay. It will be on the market once MOT'd to make room for a Triumph 500 Adventurer ( 1960's ).

[Robby]

I know these bikes inside out, in fact I was working on my project one today.

It's a fairly simple slide carb with an accelerator pump. All parts, including the pumper diaphragm, are available from NRP in Norfolk.

If it has been sitting that long, start by getting a rebuild kit, costs about 20 quid and saves a lot of cocking around. You will need to open up the accelerator pump chamber and clean it out. Expect dusty alloy corrosion on one side of the cylinder, and ancient petrol/jelly/varnish on the other side.

Don't loose the tiny O ring on the pump shaft between carb body and float bowl.

Also remove the mixture screw and blow carb cleaner through its hole. Proper screw setting is in the Haynes, about 2 turns out.

Once its all clean and back together, easiest way to start it is two turns of the throttle (to pump in some neat fuel), full choke, give it a kick.

[St George]

Thanks Robby, will have a go after work. Regards Colin

[St George]

Stripped the carb and the main jet was 90% blocked. Cleaned the whole lot and even the accelerator pump still works well. Started after a couple of kicks and ticks over when warm. The clutch is not stuck at all and selected gears OK. MOT next week if I get time. The choke does not stay out when I let go of it, is there a tensioner anywhere. Can cope if there isn't. Thanks for all the replies lads.

[Robby]

There is a grippy thing at the base of the choke lever. It works fairly well on original cables, never seems work on pattern ones, or at least it won't hold the choke full on, but seems to hold it about half on.

If it is idling well, its fine. Getting a steady idle out of them is always the hardest part.

Before you MOT it, have you checked for rot in the frame down around the footpegs? They rust badly there, I had to remake the bottom 6 inches on frame on my current one.

[St George]

All looks fine in the footrest area, it has been in a dry garage since 2005, quite time warp. Even the chrome on the forks and headlight is good. slight surface rust on swinging arm. Slight rust on spokes which comes off with a Brillo Pad. Thanks for tips.