Carburettor for 233cc Honda

[Petemate]

OK, so In have had it 'up to here' with the current VB carb on my LA250 Custom (based on the CM250C bike, and with the basic 233cc engine as on some CB250 Nighthawk and CD250U)
I have now had it to bits 3 times, ans still have the same problem, worse now the colder weather has set in. Cold start - instant with full choke. Once warmed up - goes like a bat out of hell, especially over 8k rpm. Does NOT like warming-up period, necessitating sitting with the revs at 2k for at least half a minute before dropping the choke down and setting off. Last two times I had the carb apart I gave it a good blast out with the air from my compressor, and those two tiny bleeds, which AFAIK are the progression passages, display nice jets of carb cleaner exiting them. The plugs show the mixture correct. I'm now out of ideas and I am now considering fitting a Mikuni carb. There are some on the bay but I need someone to advise the correct jetting for a Mikuni Vm 24 for a 250cc motor. I know that mine is not a 250, but a 233, but anything has to be an improvement on what I have now!!
Help
Pete
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82 not out....1983 Honda LA250 Custom
2008 Saab 9-3 1.9 Tid 150 Vector Sport estate
2005 Stirling Eccles Topaz 2-berth

[Petemate]

PS
The piston is free in the dashpot, also it holds suction perfectly, ie with the unit upside down I can hold the piston and the dashpot stays without dropping off. All the jets are clear, all the holes pass carb cleaner on both the main and needle jets. The fuel level is correct. I have the idle mixture screw set at 1 3/4 out but both my manuals have different settings. I have tried both 1 3/4 and 2 1/2 - no difference. The air filter is clean and lubed with light oil. Consumption is roughly 80 mpg, and from the spark plug electrode colours the jetting looks like it is correct. The jet sizes are as listed in the CMSL data for the carb.
H-E-L-P!
____________________
82 not out....1983 Honda LA250 Custom
2008 Saab 9-3 1.9 Tid 150 Vector Sport estate
2005 Stirling Eccles Topaz 2-berth

[Teflon-Mike]

Sounds like you have the wampy pseudo CV with cam and vacuum lifted slide. Efkin orrible thing, stick it in the bin, if it is!
'Propper' CV's, used paired on the CD250U, aren't so bad, but a PITA when they go wrong, and cheaper to replace with Chinky Copies than overhaul properly, due to bonded diaphragm.

I presume you have the single carb on a branch manifold rather than a twin-set-up?

26mm PD as sold for chinky CG engines etc; Should be direct swap, just make sure rubber O-rings are good and ft gaskets were appropriate. Jet as book for CB250 Nighthawk.

Twin 24-pd's off a CB125 Super-Dream also fit; but rubber stubs for them are getting like Hens-teeth; as jetted for the 'dream, they work remarkably efficaciously on the bigger engine's.... allegedly
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Petemate]

[Teflon-Mike]

No.
I have no idea what that is. It SAYS its a PD series carb... but it's a CV!

Try something like this:
https://www.ebay.co.uk/itm/For-The-Honda-CG125-Carburettor-Carb-Carby-48mm-Mounting-38mm-Air-Intake-/172000578728?hash=item280c088ca8:g:czQAAOSwZVhWSZWl
It's a plain slide-carb... you Know like those nice chaps at AMAL used to make, that makes the Skinners Union items look positively 'space age'! Even possibly the remote float-bowl one with a leaky hose to the main-jet! I had on my Moggy Pick-Up...

Cowly QC Rework eh? I'm surprised you ever want to see a spanner again! Ex Lucas here.
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Petemate]

[Teflon-Mike]

You're right! How odd... CMSL is showing the CV type carb for both CB-Two-Fifty 'Night-Hawk' and the CM 250 'Rebel'; YET I could have sworn they were fitted with the 26mm slider as per CD/CM200, and that is the only carb I have ever seen in the metal on that motor.

OK, lets scrap that advice; can you get a picture of your inlet manifold?

That CV seems to have a diagonal flange pattern where the sliders have a horizontal one off-set about 1/4" from the bore centre.

Provided that's the same flange the CG carb should fit; AND I'd not worry about the jetting too much util I;d bolted it up and tried it, TBH, these motors, at least the soft-cam 360 varients aren't all THAT critical. I have run a 360 timed 125 on the CCV (horrible!) and a single 24mm Super-Dream carb, (much nicer) A 360 timed 200 on its single 26mm slider, the 24mm CCV a single 24m Super-Dream carb and twn 24mm SD carbs.. that one went quite nicely, actually!

As jetted for the CG, it's likely to be not far off; its just feeding two 125cc pots, making about 10bhp each at about the same revs, one on the back-stroke to the other.

If it's much off, off, I'd then use the CD200 jetting as basis to get closer before doing any more major fiddling.
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Petemate]

Thanks Mike. I will try to post pics showing my manifold (please note these were taken BEFORE my budget[lol] resto)

I am quite heartened to see how inexpensive the Chinese carbs are - I did see once on ebay a brand new carb as fitted to mine in the US of A for several hundred pounds. Ouch. Quite why Mr Keihin should make those VB carbs so complex amazes me. The SUs I am used to were by comparison so simple and easy to work with.
____________________
82 not out....1983 Honda LA250 Custom
2008 Saab 9-3 1.9 Tid 150 Vector Sport estate
2005 Stirling Eccles Topaz 2-berth

[Petemate]

Reckon I may end up making an adaptor for the flange - there are a few CB250 manifolds on the bay so that would take care of the difference in the angles.
____________________
82 not out....1983 Honda LA250 Custom
2008 Saab 9-3 1.9 Tid 150 Vector Sport estate
2005 Stirling Eccles Topaz 2-berth

[Teflon-Mike]

To mention that Chinese emporium of mis-fortune cookies; Blugga & Borrox! That seems to have a bonded rubber stub!

You know, it might actually be just THAT that's giving the grief is the rubber is dead!

So, its a CG carb AND a Benly manifold needed then.

I have a couple of CD manifolds knocking about; if you brave crossing the Vale of the Red-Horse into the Wilds of Warks, I can dig one out for you if you are stukkered.

Trying to re-flange that would be a bit of a pain, and an exercise in futility, to make a bit that's readily available off the shelf.
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Petemate]

[Snod Blatter]

[Petemate]

[Petemate]

[Petemate]

Update.
Yesterday I received my 5 litre can of thinners/gunwash. The stripped carb, minus all soluble bits, eg plastic etc., was dutifully dunked in a container of the thinners and left until this lunchtime.
Blew the carb out with compressed air, followed by a spray through with carb cleaner, then blown out again. Reassembled the carb and refitted it. Good result - excellent start and most importantly no hesitation and fluffing/dying etc during initial warm up. After only a minute or so settled down to a nice steady idle - it would not do this before. Granted, during the warmer weather, it was not too bad but in truth I just knew that it 'wasn't right'.
My money is on some deposits lurking in those dratted slow running passages which these pesky carbs are noted for, and I hope that will be the end of it.
Reports over the next few days to follow (depending on the weather, I am chicken these days on wet roads lol)
Pete
____________________
82 not out....1983 Honda LA250 Custom
2008 Saab 9-3 1.9 Tid 150 Vector Sport estate
2005 Stirling Eccles Topaz 2-berth

[Petemate]

Had it out on the road today. First impressions good; still a bit awkward to warm up, ie have to play with the choke a bit, but at least it is not cutting out and needing as many as 6 or 7 restarts. Also much smoother on pulling away. The most obvious thing is that I can now blip the throttle normally when changing down - it had been difficult to do so before. This is excellent and makes riding the bike much more of a pleasure.
Conclusion - why did Mr Keihin make these VB carbs so damn complicated? The old diaphragm-less SU carbs I used to work with years ago were much simpler and did not suffer anything like the same during start and warm-up. Anyone who looks at the cutaway views of the VB type carb slow running passages must wonder why Keihin went that way.

https://i460.photobucket.com/albums/qq324/Petemate_01/Miscellaneous/Current%20wheels/DSC_0010s.jpg

Just look at that area behind the plug and see just how a tiny bit of muck could resist normal methods of cleaning.
Pete
____________________
82 not out....1983 Honda LA250 Custom
2008 Saab 9-3 1.9 Tid 150 Vector Sport estate
2005 Stirling Eccles Topaz 2-berth

[Petemate]

Well, a further update.
Since that last stripdown, which was a few months ago, I have been happy with the running and a few weeks ago I have started to pop in some Redex petrol additive each fill-up. About a week ago I remarked to my OH that since then the engine appeared to be running and idling really nicely. Kiss-of-death principles of course dictated that would produce a problem. The problem occurred about a week ago when I popped a few miles into the local town for a bit of shopping. I pulled up at a shop at which I frequently call and to my horror, instead of arriving and coolly slipping the 'box into neutral, the engine promptly died. Hmmm. Started it but it would not idle. So I returned home after the shopping having to keep it running by blipping the throttle. Once home, I found it would only idle by adjusting up the idle screw to the point where the revs took too long to die down. So I returned the idle screw to where it had been. I knew something was badly amiss. I don't know why, but something made me check how far out the mixture screw was - OK, I screwed it in and it was 1 3/4 which was what I had previously set it at. Out it came 1 3/4 again. Odd: imagine my surprise when I started it and the idle was again perfect at around 1300. I can only assume that there had been a bit of debris floating around somewhere in that labyrinth of slow running passages and somehow I had disturbed it with the mixture screw. Having learned my lesson, I will go through the summer and when winter comes if I get even the slightest 'sniff' of anything other than nice even running, I will remove the carb again, strip it and get it ultrasonically cleaned.
Currently I have the feeling that the carb has now decided to behave, as I now need hardly any choke to start the bike and it is really smooth, also settles to an even idle soon after starting. Furthermore, even when thoroughly warm (eg after wringing the bike's neck at an indicated 75+ mph en route to the local bike meets) the idle is still 1300 instead of rising to over 1500. Whayhay.
Sorry for the length of post! Entertainment for the masses lol.
Pete
____________________
82 not out....1983 Honda LA250 Custom
2008 Saab 9-3 1.9 Tid 150 Vector Sport estate
2005 Stirling Eccles Topaz 2-berth

[spottedtango]

I meant to ask are you using an inline a fuel filter? I'd stick one of them on as a preventative measure

[Petemate]

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[Petemate]

[Snod Blatter]

[pike]

[Snod Blatter]

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