Topic: CB400 four running rich

[Polio]

Hello everybody,
I'm having the same exact problem as this guy:  http://forums.sohc4.net/index.php?topic=90685.0
The carbs have been rejetted recently and cleaned multiple times, but still the sparkplugs get fouled in just 20-30km.

I tried fixing the fuel level but I can't manage to get it right, I'm thinking about replacing floats and valves eventually but they don't look worn.
Any help is appreciated.

[harisuluv]

Polio we can't really help you without actual information.  Instead of saying you rejetted, tell us WHAT they were/are rejetted to now.

What is the air filter setup, exhaust mods?  What are the floats set to? 

We can't help you without basic information.  If you want real help, post pictures.

[Polio]

It's rejetted to standard specs: 75 main jet and 40 slow jet with an original honda kit.
No exhaust mod, it's a marving reproduction with the original collector and pipes, original aribox and air filter.
The floats are set to 21mm.

I can take pictures of the jets and float valves, anything else? 

Edit: added photos.

I was having some trouble removing one of the jet needle set, when I got it out I realized it's slightly bent and one of the hole looks very slightly out of place,
not really noticeable in the picture but it's clear at naked eye.
I doubt this is what's causing all 4 plugs to get carbon fouled tough. 

[Bodi]

What problem do you have with the float setting? The picture you show of the float tang and fill valve looks OK. How are you adjusting them? Replacing the valves is only needed if/when they leak and as with any jets, OEM ones are preferable to aftermarket (but cost much more).
The emulsion tubes shown look fine. One hole slightly out of place won't be a big deal.
Are the needles set correctly (middle slot is standard)?
Is the choke working properly and opening with all four flat across the throats?

[Polio]

What problem do you have with the float setting?

No matter how I set them I can't make the bike idle properly, I'm using a credit card cut with a 21mm slot to set them.
I think the needles are set correctly yes, not sure what part you're referring as "middle slot" tough.
Yes the choke is opening properly.

[harisuluv]

Thanks for the pictures

the bend in your emulsion tubes is not really a big deal, but it doesn't show the opening where the needle would go in.  if it was taken out incorrectly it's very easy to damage/widen the opening.  That is enough to produce the symptoms you are describing.

Did you do a bench sync/vacuum sync?  mixture screw settings set at? 

[Polio]

There's no visible damage to them as far as I can tell, but I haven't changed them yet.
mixture screw is two and half turns out more or less.

I don't have acces to a vacuum gauge so no I haven't done it, I'll have to get one because I had to remove one of the needles body to get the tube out from the top.

Tried to take a picture of them but with poor results.

[harisuluv]

Hi Polio, that's the wrong end of the emulsion tube.  No fuel metering on that end, the other side is where the needle goes in and it is more critical it is in good condition.

Mixture 2.5 times out is way too far out.  Probably not even actually doing anything that far out.  There is a pretty small range of adjustment.  Try 1.5 out. 

Btw what do you mean by rejetted with an original honda kit?  Honda doesn't make any rebuild kits.  Only gasket set.

[Polio]

Sorry I forgot to upload the other picture,
the manual says the mixture screw should be set between 2 and 2.5 full turns out, besides isn't a smaller ajustment going to make the mixture even more rich?

I meant I used an OEM kit, the parts are branded keihin of course.
but I only replaced jets and float valves, I'm thinking maybe if a complete rebuild would solve the problem.

I also tried a new sparkplug on all four in case the ignition coils were causing a weak spark, with both cold and warmed up bike the spark seems fine.

Sparks video:
http://gfycat.com/HilariousSoftBarracuda
http://gfycat.com/VainUnluckyBufflehead

[harisuluv]

Turning in will make it richer, but after 1.5 it might not do anything really.  You could go to 5 turns out and it would probably be the same as around 2 or less.  Point being, it's not actually leaning it out at that far out, and the problem is something else.

From the picture, the main jet looks like it has a beveled edge.  Real Kei Hin jets don't look like that.  If it has a "K" logo on it, it is probably a "cruzinimage" kit which is available on ebay or related to it.  They will stamp on a fake Kei Hin "K" logo.  Even the logo is stamped poorly.  You sure your needles are Kei Hin parts too?

Emulsion tubes have seen some superficial gouges in them, if the important dimensions are enough to cause your problems, who knows.

When we reference the needle jet, we're talking about the actual brass needle looking part sticking out of the slide.  It has a clip with five slots, if should be in the third slot (middle).

[Polio]

I'll get to the mixture screw once I put the carbs back togheter.

You're right, it does have a slight bevel.
The needles have a the keihin brand on them but as you said they might be just a reproduction.

At this point it's pretty clear I can't pin point the issue to anything in particular, so I'll just order a complete carb rebuild kit,
I'll make sure it's original this time and I hope the problem will be fixed.

[harisuluv]

the needles are probably real, I don't think they fake stamp those, the aftermarket needles i think are made by maybe one supplier and it goes in a few kits.  they are usually stamped D22, D2x something like that.  The repops also have relatively loose clips compared to the real ones. The little circlips will jiggle around a bit.

As said before, an OEM kit doesn't exist, but even buying the components individually might not be so easy, as the 75 mains are no longer an available part OEM.  The 40 is available luckily (for your 400f), the 350F 35 slow jets are not however.

Also, I have fixed problems similar to yours by just changing the mixture screw, as the taper is different.  Again, the OEM screw has a K logo on it, but the fake ones sometimes do too.  Usually it's pretty obvious from the condition of the brass.  If it looks kinda new and shiny then it's probably a repop.

These carbs can be pretty straightforward if you're dealing with an unmolested set, however after 40+ years a lot of the times you're not going to be the first person to get into them. 

I don't think the main is probably a real problem though, and you're not even having an issue at wide open throttle (WOT), that repop jet is probably ok.  post some other pictures of your parts, I can probably tell you if anything is obvious. 

[Polio]

I haven't removed the other needles yet, but the clip on the one I have on hand is pretty sturdy and doesn't move at all.

Oh I didn't understand that, I actually got a message from a seller on ebay and confirmed that the kit I was about to buy as actually a keyster kit.
This carb is far from being unmolested, I'm the 6th owner and somebody down the line probably had an open exhaust because when I bought it it had bigger jets.

Well the plugs get carbon fouled pretty quickly even while I'm using it, but right now I can't get a stable idle speed so I haven't tried just letting the bike idle for a while to see if the slow jet it's involved in the problem.

More pictures to come.