CB400F Carb overhaul

[Lobo]

Ok, into the actual rebuild now...

I note that the choke butterflies are sprung closed.... meaning that should the grub screw (whatever) in the main choke lever linkage 'let go' all four carbs will go full choke & the engine stop.  Seems somewhat unsafe if your doing 80 mph in the outside lane at the time; should I be worried / mod this - or have those wretched elf'n'safety types finally got to me? (Odd little things on these old Hondas do surprise me - eg my K2's single 15A fuse supplying... everything. Low beam to high beam in a turn one night... blow the fuse...coils shut down...work cut out!)

Also, staying on this choke lever linkage (and noting no components bent / modded (yet!)) it appears I can't quite set it up to give BOTH full choke and 'WOT' settings due insufficient choke lever rotation. If I set the butterflies to full close, then at 'ball bearing engagement' / choke OFF setting the butterflies are not parallel to airflow, but about 10 degs inclined. Looking straight on they're just about within the confines of the shaft profile. Again... a slight mod needed?... filing a tad off the backside lever pivot brass limiter nipple?...... or normal / don't fret?

Finally - the small screws that attach the choke butterflies to their shafts. Best way to ensure they don't vibrate free....Loctite... or what? Appreciate they're in the fresh air side of the carb, but nonetheless concerned stray petrol vapour may ultimately break that bond?.  Could, I guess disassemble the sliders / needles out & 'rivet'  the threads whilst back-supporting the screw heads....but not really wanting to take a hammer anywhere near my carbs!

Thanks in anticipation...

[Ewan 500 K1]

Anybody know if these are the same as a 500/4 as i need two for mine.

£12.50 for two from Holland on ebay

http://www.ebay.co.uk/itm/Honda-CB500-CB550-CB350-CB400-Four-set-reproduced-carb-stabilizer-springs-/121073360635?pt=UK_Motorcycle_Parts&hash=item1c3088defb

[K2-K6]

I thought someone else would pick up the choke position question......but I'll add my bit for what it's worth.

I'd set the butterflies to be a best position at full open, then accept any compromise at the closed/choked position. They just don't seem to need absolutely closed chokes to start in most of our climate conditions and you very quickly back it off anyway almost as soon as it's fired so shouldn't really make any real compromise. Not sure if this would be a text book method, but seems logical on a fairly small carb to help maximum flow and to make sure it's running when warmed up without having any undesirable choke/mixture effect during normal running.


As regards the failure of the operation which would force a closed choke situation, I've not heard of any doing this but Bryan may be able to bring more to this from his experiences.

[Lobo]

Thanks K2-K6

That sounds sensible - don't particularly want to be filing down nipples etc & making it all look a bit bodged.

Q...if the butterfly is at say 10 degs off horizontal (open) but contained within the profile of its shaft (looking down the carb throat) will WOT performance suffer? ie MUST the choke (OFF) be absolutely parallel to airflow? If you reckon not then I can indeed get full choke ON.

Q. Care to comment on (red) Loctite holding the fastening screws on the choke valves versus the originally 'punched' protruding ends  forcing them oversize? Should I worry?

And yup,  I'm thinking health & safety morons getting to me... if just one person had demised as a result I suspect would have been sorted long ago....

Thanks again.

[K2-K6]

Now there's a big question, about butterfly angle I mean. The fact that it is there is producing the most obstruction I guess, as opposed to a racing carb with no choke facility to restrict it at all.

I'd guess that there would be next to no measurable difference if as you describe they are contained within the diameter of the spindle, but you'd never be able to tell without accurate measurement anyway....apart from a verified top speed run or dyno session....In short I'd not worry about it at that deviation.

Red locktite 271 fits the application as far as I can see.......i.e. a virtually permanent locking function that takes a considerable level of heat (spec says 250degC) to in any way effect a dissasembly of the parts once it's set......assume that the parts are fully degreased prior to application.

I know there are others that will only accept a mechanical locking method if used orignally, so you have to really make a choice for yourself.

The doubters will probably all be flying in plastic aeroplanes soon (Boeing dreamliner et al) that'll scare them.

Maybe somebody else can offer their experience on the locktite question to help you........

[Bryanj]

Must admit to never having removed the choke plate screws, for the simple reason that i didn't fancy having to refix them!! As to airflow these carbs are, in my opinion, such an old and agricultural design that a disturbance of airflow was not even considered when thewy were built.
i have in fact been on the motorway with a 500 when the leggings knocked the choke lever on and yes it does slow down quick but not as bad as an engine seize!!

[Lobo]

Thanks K2/6, Bryan,

Job done, will be months before I can verify all upto scratch as engine about to go for recon and thence (with summer leave) will rebuild the bike.

Still totally 'befuddled' as to why the darned set-up has to be so complicated - from my untrained eye it all appears to offer nothing over the simpler 750/K2 onwards carbs.

Below the finished product - painted & lacquered in petrol resistant finish.  Would have dearly liked them vapour-blasted & plated etc.... but living here in a third world country and re-conditioning bits you've dragged back in yer suitcase has limitations! Vapour-blasting etc may arrive here in oh...50 yrs. If the finish doesn't wear well it only has to last a couple of years to my perm return & then will do it all over again....ugh.

Cheers & thanks to all for the various inputs - the balancer SS tie pieces await me in Hampshire..I hope.

[Lynx]

Just make sure you put them on the right way up  .

[Lobo]

Thanks OddJob, will sleep a little better on the choke flap screws comment. If you're a glutton for punishment, sure, spend hours cleaning, spraying, lacquering....or simply bung the bits in a box & take 'em somewhere to be zinc plated whatever, at a reasonable cost! (I'm assuming you live somewhere that can offer such a service). Bonus is they'll come back original looking.

Or, how's about.....http://www.gaterosplating.co.uk/Zinc-Plating-kit.php. 
Gawd I wish I were back...(this stuff not allowed an aeroplane)

Yup, as in my last sentence, (and not knowing their correct name) those 'links' await me in Hampshire and will be fitted once I get home this summer.
Cheers...

[Lynx]

Does anyone know where to get, or what to use for those felt 'washers' in the carbs where the linkage shafts go in? Mine are even broken or lost  .

Cheers

[sweetpeauk]

If you join the yahoo group "cb400F" there is a PDF in the files section that explains how to make your own.

Paul

[Lynx]

Thanks Paul,

I've just had  look on Yahoo. I did a search in groups on CB400F but it just seemed to be Spanish. It that the one?

Cheers
Steve

[Lobo]

I had a go at making mine - but to be honest not a success for various reasons. A bit of a find but I got a job lot of small rubber 'O' rings which appeared to be exactly the size required.... and used those.

If you do go this route suggest you check first that your o-rings 'petrol proof'

Gotta admit to being unsure of the exact job of felt vs rubber, but did pack a dollop of grease within the flanged washer 'housing'. Suspect my rubber o-rings more air tight - but really of little concern as in the atmospheric / choke side of the carb.

[sweetpeauk]

Try this link,
http://autos.groups.yahoo.com/group/cb400f/
you will need approval to see the group info. There is lots of useful stuff on there so worth checking out.
or you could PM me your Email and I will mail you the PDF

[Lobo]

Hi OddJob...fully understood & appreciated, I should have noted your 'Top end fixer' moniker and realised your experience! I'm personally the least 'arty' person I know and any deviation from the original just looks like a cock-up.

And yup, accept the attached pic looks tacky.... but can anyone advise whether this choke sticker & red paint (on the actual lever) were standard on the UK 400F2s.... I don't remember this from 1978.

(the pic from a DSS 400F2)

Ta...