Topic: '75 CB400F carb question

[StevieMac]

I've got a friend with one of these bikes and he's having a carb problem.  #3 cylinder isn't firing when it's idling.  If you turn up the throttle it starts working.  We just discovered the problem when he was leaving work for lunch.  I happened to be standing there when he started it up and I noticed it wasn't running on all four.   We couldn't do much in the way of investigating here at work but I'd say the pilot jet on #3 is plugged.

Now to my question,
If I remove the float bowl on that carb will I be able to get the jet out to clean it and re-assemble everything without removing the carbs from the bike?  On my '72 500K I know it's pretty friggin' impossible to re-assemble in that state because of how the float bowl holds the main jet retaining clip in place (the main jet just keeps popping out, at least in my experience).  On my '78 750 there is no such problem.

[GroovieGhoulie]

If you have the tools, it might be possible.

I know that the 750 has clips to retain the carb bowls, but the 400F has screws, and VERY soft screws at that, so unless it's done carefully, the screws will strip.

I think it would be harder to do it on the bike than just taking the carb bank off (the nightmare that THAT is).  If it was an outside carb, I think you'd be OK, but an inside carb would be a royal pain.

[StevieMac]

I have a funky screw driver that should let me get the bowl off without a problem (not TOO much problem at least!).   I've done it successfully on my 750 more than once (all 4 bowls too...) so that's not really my concern.  It's more if I'll have a problem with clips or jets falling out like they do on my 500 when the carbs are mounted on the bike.

[GroovieGhoulie]

I've had my carbs horizontal before and I didn't have any problems with jets falling out.  Of course the mains were REALLY stuck in there from the rubber gasket being so fat.  In my carbs anyway, the spring clip is sorta superflous, since the first time I tore them down for cleaning and work, one carb HAD no clip and the jet was nice and tidy in its spot.  Had run it for about 500 miles before that with no problems, so I was shocked to see no clip there.  I cannibalized a set of 500 carbs for a clip, which fit perfectly.

[aptech77]

A good 90'deg driver works well.

[TwoTired]

It's been a while since I did a Cb400F.  But, I remember carb removal was much more of a pain than on the cb500/550.

I'd be inclined to attempt slow jet cleaning with the carbs in situ.

The inner carbs are, indeed more difficult to work on.  However, for me, I found that removing the bowls from the outer carbs makes seeing what you are doing on the inner ones much easier, and feasible.  Critical, is the correct length #2 screwdriver for accessing the bowl screws.  That simple purchase removed many curses from the proceedure.  Magnetizing the tip can help with screw install, too.

The main jet fallout problem is related to the jet oring.  New ones resist seating.  A little grease allows the jet and oring to slide fully into place and then exert side retention pressure on the housing to hold itself in while the bowl is installed.  I know, lubing it sounds like it would be worse.  But, it sure helped for me. Along with twisting the jet into the seat a little.

Cheers,

[StevieMac]

Thanks for the grease tip TwoTired!  That's great!

One more question, are the pilots press fit or threaded on these carbs?

[GroovieGhoulie]

IIRC, they are threaded.

[StevieMac]

You guys rock!  Thanks