Topic: Can clogged emulsion tubes like this cause rich sooty plugs? (PICTURE)

[PeWe]

Guys, you want to see blocked emulsion tubes, look no further!!  pulled these bad boys from my 1977 Honda CB400F

Look like something from a sunken ship found south east of Florida Keys....

[oldhatt45]

PeWe,

I have been diving on the WIlke's Barre off the Keys and Trust me, that wreck looks better than the emulsion tubes that Cb400fnoel showed the picture of.     

Charlie

[Cb400fnoel]

Guys;
done a complete carb clean, new emulsion tubes and needles, the lot, bike splutters 2000-4000rpm, eg if i was in 3rd gear at 2500rpm and put on full trottle bike would just splutter i have to gently feed in trottle until i get over 4000rpm, if i gun bike in every gear not a problem, bike idles perfectly but cant get around this splutter.
bike to be honest is running basically pretty much as it was with the dirty emulsion tubes you seen in earlier post,

Whats the problem?

[harisuluv]

Guys;
done a complete carb clean, new emulsion tubes and needles, the lot, bike splutters 2000-4000rpm, eg if i was in 3rd gear at 2500rpm and put on full trottle bike would just splutter i have to gently feed in trottle until i get over 4000rpm, if i gun bike in every gear not a problem, bike idles perfectly but cant get around this splutter.
bike to be honest is running basically pretty much as it was with the dirty emulsion tubes you seen in earlier post,

Whats the problem?

No one is going to be able to give you very insightful information if you don't give information back.  I assume cb400f is the bike we're talking about from your name?

exhaust/air intake/pods/no pods/year/mileage etc etc etc etc

[MoMo]

If it will not take full throttle at 2500 that is almost normal for a bike that does not develop power until 4500 and up

[Cb400fnoel]

Folks, it's all stock, air filter (new) Dave silver, exhaust (original)  deluxe jet kit from nrp-carbs, all stock sizes, plus float height was 21.5mm, year 1977 cb400f mileage 49600 miles, was out this evening on it, bike starts on the button cold or hot no problems, idles cold or hot no problem,  as I say if you horse it up through the gears to 80 there's no problems at all, it's only when riding slowly at 2 or 3000 rpm there no way you could just open the trottle, you have to (3rd gear up) really feed in the trottle until above 4000 rpm then away you go,

[Cb400fnoel]

Should also have added that timing is perfect and points gap perfect, timing also moves upon increasing rpm, new points were set with lamp and then checked with strobe.

[harisuluv]

What are the actual size of the pilots and main?  Did you get specifically a "jet kit" or a rebuild kit?  I went to that site and didn't see a jet kit, so I'm assuming you meant the deluxe rebuild kit?  If you used that brass (looks like you used the mixture screw too) well, that's probably your problem.

If you used the needles from that kit, well, that's 9/10 your problem.  They're garbage, totally different taper from OEM, and the needle would basically affect that throttle range you are having issues at.

[Cb400fnoel]

got the Premium carb kit,

If youre pretty sure the needles in the kit are crap Ill get emulsion tubes and needles from Dave Silver, asap.

Jets are MJ75/PJ40, are these ok from the kit? (Honda CB400F CB400/4 Keyster Premium carb kit [Keihin] )

What about float height, 21.5mm, admitially i had carbs resting upside down when messureing, ive read this is wrong also, they need to be on their side,
What height is best?

[lrutt]

I always use a single strand of wire from a wire brush to clean those small holes. Air and cleaner doesn't always get them completely clean.

[flybox1]

Folks, it's all stock, air filter (new) Dave silver, exhaust (original)  deluxe jet kit from nrp-carbs, all stock sizes, plus float height was 21.5mm, year 1977 cb400f mileage 49600 miles, was out this evening on it, bike starts on the button cold or hot no problems, idles cold or hot no problem,  as I say if you horse it up through the gears to 80 there's no problems at all, it's only when riding slowly at 2 or 3000 rpm there no way you could just open the trottle, you have to (3rd gear up) really feed in the trottle until above 4000 rpm then away you go,

Your probably just a tad lean up to 3500rpm.  Your mixture screws could adjust that out.
Otherwise, your fuel level and plug color look good..

[harisuluv]

got the Premium carb kit,

If youre pretty sure the needles in the kit are crap Ill get emulsion tubes and needles from Dave Silver, asap.

Jets are MJ75/PJ40, are these ok from the kit? (Honda CB400F CB400/4 Keyster Premium carb kit [Keihin] )

What about float height, 21.5mm, admitially i had carbs resting upside down when messureing, ive read this is wrong also, they need to be on their side,
What height is best?

yes, do a search on needles, most all members on here will reuse their needles and brass if they can.  it's probably fine to use your old ones.  a new set of needles and tubes is going to be around $100 or more.

[Cb400fnoel]

The problem is that the old needles i can physically feel a worn step at the top of them, ive the air screws out 2 1/2 turns, i was using a clear plug to set these and this was the point when all was so sweet, fireing nice and blue.  So i might give them all a turn in and try that, but ive no hesitation getting new needles if need be,

[Cb400fnoel]

Folks, the air screws ranged from 1 1/2 to 2 turns out, give all four 1/2 turn in but no difference.

[harisuluv]

yeah that step at the top is not necessarily wear.  it's very noticeable on the 750 needles, not so much the others.  i think they have at least some prominence new.  it is common to have less effectiveness with the air screw adjustment with aftermarkets.  the taper is different so the stock settings are only a ballpark to go from anyways.

[Cb400fnoel]

I put the air screws all back were they were,

Also, on the needle, im going to return the original needles, what notch would you put the clip in? its currently in middle same at the original however the bike had the same symptoms at the same RPM, i should return the original air screws as well and reset this using the clear plug.

In my opinion (but im no bike tuning person by any means), it almost sounds like the bike is getting to much fuel (not to little) once you pull the throttle full open at 2500rpm -3500rpm it bogs down, you’ve to ease off the throttle for a bit say, half ways and once bike is firing again on all cylinders gradually open  & once over 4000rpm you can hit full throttle no problem.

From a standing start, full throttle in all gears isn’t a problem, bike hits 80mph with not a lot of difficulty. 0-60mph is very good, probably around 7 sec.  JUst need this bubbleing sorted.

[HondaMan]

I put the air screws all back were they were,

Also, on the needle, im going to return the original needles, what notch would you put the clip in? its currently in middle same at the original however the bike had the same symptoms at the same RPM, i should return the original air screws as well and reset this using the clear plug.

In my opinion (but im no bike tuning person by any means), it almost sounds like the bike is getting to much fuel (not to little) once you pull the throttle full open at 2500rpm -3500rpm it bogs down, you’ve to ease off the throttle for a bit say, half ways and once bike is firing again on all cylinders gradually open  & once over 4000rpm you can hit full throttle no problem.

From a standing start, full throttle in all gears isn’t a problem, bike hits 80mph with not a lot of difficulty. 0-60mph is very good, probably around 7 sec.  JUst need this bubbleing sorted.

It's VERY good that you are going back to the OEM needles (hopefully they ARE the OEM needles), because the Keyster needles are crap (or whatever other 4-letter work describes "don't work in these bikes"). I have YET to see them work from ANY Keyster kit in these Fours. Keyster just doesn't get it...

The 350F/400F bikes are touchy about several things in the lower RPM range:
1. Jetting: they use very small KEIHIN jets, like $75 or #78 size.
2. They hate foam air filters, paper is better. Making your own from a K&N is excellent.
3. The sparkplug caps must be closely matched in ohms, or one side hogs all the spark. This usually shows up as a flat spot in the lower RPM ranges, like you're describing. The OEM caps were 7500 ohms on the 350F and the first 400F had these, later ones had 10,000 ohm caps. The former must be within 800 ohms of each other on a coil, the latter within 1000 ohms.
4. The O-rings between the carb-hose castings and the head get hard after 5-8 years: if yours are not new, they are probably hard as plastic and leak vacuum. This, too, causes poor low-end throttle response. Also, make sure the hose clamps are tight and the hoses are not split.

That's where I'd start, if it were here?

[Cb400fnoel]

Folks, loads of info there, still havnt done carb strip down, might wait till winter and do it then, at mo our weather is so crap it's just a case of grabbing the sun shining and head out when I can, I give bike a 1000 mile service a one thing I noticed I'm not getting to full timing advance, points gap on both sets perfect, strobe light shows 1&4 on f1.4 and also 2&3 on f2.3, for this I used cylinder leads 4 & 2, advance unit I removed and checked, it's working ok, no tightness and springs are good, so all is great at 1200rpm, but putting revs upto 2500 or even more the advance timing is not achieved, although timings advance it stops short of the correct llocation, I deally according to manual it should be between two marks but it's not, it about 2 maybe 3 mm short of that position.

[Deltarider]

As a rule of thumb one should focus on a correct timing @ full advance and just accept what timing @ idle comes with it. With stock breakerpoints you could readjust the pointsgap and then have the full range of advance no doubt. Í have once tested it out by having exactly the right dwell (breakerpoints gap) and this resulted in a perfect timing with both plates exactly in the middle of their adjusting range. That's how accurate Honda designed their parts. With aftermarket breakerpoints you'll never know what will happen.

[Cb400fnoel]

Yes, interesting, I will do this tomorrow, I'll time with strobe light at full advance around 2500 rpm, it'll be interesting to see how engine idles!

[alacrity]

and that 400f didn't run, did it?

[Cb400fnoel]

Yes it ran all the time!

Now regards advance timing, moved main back plate and set on 1.4, checked points, all ok, set 2.3 and needed the 2.3 points plate needed a little move, recheck 2.3 points & still ok, so now recheck all and all between advance timing marks ok, weird thing is that on idle 1.4 is still perfect at both idle and full advance at 2500rpm also within the advance timing marks, 2.3 is slightly out on idle but as close as dam it, it perfectly within advance timing, cb400f can sit at 80mph (with me upright) with little difficulty, don't know if there was much left if opened full and put the head down. There'll soon be 50000 miles, tanks guys on all the info, I can't face the carbs yet,
One thing I've learned is that unless it's OEM equipment it probably crap and won't help at all, in fact throw a spanner into repairs.