CB400F Carb overhaul

[K2-K6]

Just to add a bit about making your own; the feeler guages may offer you quite a resistance to shape them well/drill holes as the material spec calls for a fairly hard spring steel if they are of decent quality.

A more useful scource could be a discarded stainless kitchen sink to give you that thickness of material.

If you were to drill two holes the correct distance apart in the steel, then sandwich in between two pieces of plywood clamped with bolts and nuts through the holes, then it would allow you to shape them by hand without bending them. Also you can make more than one at a time in the same clamp to halve your work.

[Lobo]

Thanks K2-K6,

Already gone down the clamping route; using aluminium sheet & abbuting peripheral rivets to hold the 'feelers' rock steady within. (the back of the pop-rivets then sit into corresponding holes of a large wooden block to resist twisting in the drill press)

The feelers I've used are .35mm & .40mm, ie two of each sandwiched, to give 4 pieces.

After I get (the bloody difficult holes drilled) I will rivet through those (now including large washers to give external radius) and keeping the sandwich in tact then grind the shape.

Well, that's the theory...

.....and in the meantime will keep an eye on ebay etc - thanks to Steve400//4

Cheers!

[Lobo]

Any Tec guru out there care to explain wht the 400F carbs so 'complicated' versus the older CB750's? Specifically the lifter mechanism, which on the 400 appears overly complicated with sliders, springs, elbow sockets, fancy dust seals...versus a good old up/down external vertical lifter?

Ta.

[Bitsa (Ralph Wright - RIP)]

lobo,

Dead right  complicated and fiddly all those years ago I hated them.Luckily the only 400/4 I restored the carbs apart from usual cream krackered o rings and cleaning I did not need to take them to bits.No help to you but I would take lots of pics when you attempt to do them.
Cheers
Bitsa

[Lynx]

It does say 350, 400, 500 ,550 in the title.
I tried doing a bit of research on it but all I found was Honda part Nos. for the assemblies including this part is 16029-323-004 and 16030-323-004 fits CB400 and CB550.

[Bryanj]

323 middle number is oruginaly 500 four

[K2-K6]

Lobo, your question about the complexity of the 400/4 carb linkage versus the CB750; the carb slide travelling vertically is lifted by the rotating arms so giving two seperate paths of travel...the sliding action of the lifter forks is fairly crude in it's junction with the slides and maybe a bit high on friction but very simple and, it seems, without many real problems even after all these years.

The 400 one however, when you remove that single sliding link, then needs an elbow to connect the two different paths of travel. To maintain a stability and parity between each linkage then simply requires a far more detailed set of components (as you've found) and although it may offer a solution in pure technical terms it may have lost sight of any advantage it could hold.

Honda certainly do this fairly often.....a good example is the enclosed disc brakes used of a CBX550...have a look to see how complicated they made those !!

[Lynx]

The German guy selling the spring steel replacements on eBay will do a Buy It Now price and will take payment by PayPal. Mine arrived in super quick time.

[Lobo]

Thanks gents... Lynx ta, but a day after starting my own ss connectors found a couple of 2nd hand ones on ebay which will do the trick.

K2, yup still confused as to 'why?!'. This linkage mechanism would have had to get past many folk in Honda including the accountants, each who will have been aware of the extra complexity & cost...aware too a simpler in-house solution that was working fine on their '750.

As for friction...I'm not convinced, there are so many extra components in this deign that the summation of system friction is surely greater. Certainly to my non-calibrated oaf hands there is no appreciable difference.

The only thought I have is perhaps an effort to minimise/delete all slop/play arriving at the slider. The 750 K1 (onwards) fork lifter both pulled & pushed - though any play here could have been easily 'sorted' with a 'big' spring against the slider (a-la earlier K0?). The 400's system with spring clamped elbows / connectors etc presumably keeps all slop out, and therefore the carbs balanced at all times.

BUT, whilst I'm curious I'm no engineer... always keen to learn, and just guessing..

[Bryanj]

Ah, but the carbs were not a Honda part but bought in as an assembly at an agreed price

[K2-K6]

I thought that after I'd replied Bryan, they usually use Kiehin or have done historically.....but the design spec would usually go out to the supplier and then test and approval would happen during development prior to ramping up for production once it met expectations.

Lobo, you're right in the sense that looking back on it now, then it seems to offer complication along with no really significant and obvious advance over the 750 spec......saying that though, it's easier to look back and see that now........also during original design the thought that they would last this long and someone would want to renovate them just didn't seem to exist in the manufacturing proccess then.....doubt it does now either.

Also we were seeing some of the last pure slide operated carbs generally at that time as development was heading toward CV type carbs for road bikes in which the throttle just opens a butterfly flap with the slide just opened via a vaccum circuit....these sohc motors being design decendants of the sixties Honda road racers, with Honda's managment keen to show any level of sophistication as a marketing plan/advantage.

[mickwinf]

now parts are available from gerbens1956 http://www.ebay.co.uk/itm/Honda-CB500-CB550-CB350-CB400-Four-set-reproduced-carb-stabilizer-springs-/121073360635?pt=UK_Motorcycle_Parts&hash=item1c3088defb  and he speaks english!!

[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.