Topic: cb550 still fouling plugs

[harisuluv]

saw you had the floats set to 21.  the stock setting is 22.  setting them to 26 imo would be going the wrong direction, that is a radical change.  Keep in mind that a 1mm change in float height setting, doesn't necessarily translate to a direct relation in fuel level height in bowl.

Floats are often tweaked, remember that the float height setting is based on a normal float.  Tangs can get bent weird, floats pivoted in different areas.  Will that crazy float height setting lower the fuel level in the bowl?  Yup, probably.  But if I have a hole in my boat, I can pay a guy to fix the hole or pay him to keep pumping water out.  Both will address the problem but one is better.  Try 22mm, make sure your floats are not tweaked (i always tell people pictures!) and then go from there.

[78whiteorbs]

saw you had the floats set to 21.  the stock setting is 22.  setting them to 26 imo would be going the wrong direction, that is a radical change.  Keep in mind that a 1mm change in float height setting, doesn't necessarily translate to a direct relation in fuel level height in bowl.

Floats are often tweaked, remember that the float height setting is based on a normal float.  Tangs can get bent weird, floats pivoted in different areas.  Will that crazy float height setting lower the fuel level in the bowl?  Yup, probably.  But if I have a hole in my boat, I can pay a guy to fix the hole or pay him to keep pumping water out.  Both will address the problem but one is better.  Try 22mm, make sure your floats are not tweaked (i always tell people pictures!) and then go from there.

That was a typo on my part . They were set at 22mm exactly with brand new needle valves . The level in the bowls were even with the gasket surface. Good point about 1 mm of float height not equalling a 18mm drop on the fuel level in the bowl. I will first clear tube em to see that they are way low, then maybe bring the floats back to 24 and check again till they are right at 4 mm below gasket surface . I think all the tangs where bent weird, lol. Will snap a vid tomorrow.

[Scott S]

A thread from Scott S who was having a fouling problem and eluded towards the end he may have had the mains in backwards as there are confusingly two or ing grooves on the main jets.

 It was just the one. Only #4 was fouling. Hey......$H1+ happens sometimes.   I'm hoping the roads stay dry enough today to test it out.

[78whiteorbs]

Well dang, still not right. Set float height to 24mm and clear tubed it and it looked just right. Put everything back on the bike cranked her up and she ran great. Nice and crisp with excellent  throttle  response. Synced the carbs and after running about 5 minutes the carbs started loading up an 8 stroking. Turged the fuel tap off on my auxiliary  tank and reed it up for a bit and observed it cleared right up and was again running nice and crisp as it should and revved perfect. Leading me to believe the needles are not shutting the gas totally off and slowly loading it up. I tested them when the carb was off by blowing in the gas line in and when I manually raised the floats/ needles they shut the airflow off on 3 of them. On one if I put more than a light pressure  of air from my lungs I could here it bubbling up past an oring I think. It wasn't completely off like the other cylinders. These are brand new seats with brand new oring. Ony thing I could think is that something in the carb body itself was causing this oring to not seal. I think the bike went alot  longer without fouling because of the lower float seriously about to buy another carb rack....:-(  . I have done like 10 sets of carbs no problem until this little it's so nice out and I wanna ride!

[harisuluv]

78whiteorbs please post some pictures.

[78whiteorbs]

Will do

[78whiteorbs]

If one needle valve was not shutting the fuel off or was slightly leaking there's no way it could effect the other three right? Just that one would eventually foul . Also it is not pissing out the overflow so its loading up enough to cause a rich condition but not high enough to puke out the over flow.
 Does this make sense?
I feel I am so close here....

[mrfish2]

Turged the fuel tap off on my auxiliary  tank and reed it up for a bit and observed it cleared right up and was again running nice and crisp as it should and revved perfect.

I'm still right there with ya. With the petcock off mine runs great but as soon as I turn the petcock back on the fuel doesn't flow correctly, even with correctly set fuel level in the bowls.

You think maybe because the needle valves aren't Keihin parts that they don't sit right in the carbs? I remember when installing they ones I got in a rebuild kit they weren't quite the same fitment as the originals.

[78whiteorbs]

I still have the originals and I thought about replacing them back Mr fiSh. I don't recall that a difference if any. Most the stuff I have got from 4 into1 has been on point.

[mrfish2]

Well at least yours will idle. Mine won't idle at all if the petcock is on, it'll just bog down and die. Does yours blow any black smoke?

[78whiteorbs]

Not at all till it starts 8 stroking then it will a little on cylinder number 4. have you tested the valves  by blowing in the fuel lines with the bowls off?I read somewhere there are 6 over flow vents. Four on each bowl and two in the top. I once had a problem with a k8 cb750 were the vent was clogged and it cause some drama. I am not sure were  or if this have top vent circuits or not maybe somebody else knows..

[DH]

Orbs, have you tried clear tubing them installed on the bike? Open the fuel valve and watch them, check to see if they indeed are overfilling and contributing to richness...give them some time.

[78whiteorbs]

I have and they hold steady haven't done it while running the engine or for extended periods of time. Maybe two minutes max with fuel source open. This is why I was thinking it was a very slow leak in there. I bet if I clear tube em and then run the bike when it starts to rise is when the engine will start running crap-

[DH]

IF that is happening, you could be right., but BE CAREFUL DOING IT THAT WAY if you do. No gas leaks! Get an assistant if you need and a fire extinguisher.
Probably not the best of ideas tho.....maybe somone with safer suggestion?

[Scott S]

 The other two vents are in the center of the carb rack.

[mrfish2]

The other two vents are in the center of the carb rack.

Is it absolutely necessary to have tubes running from those vents?

[78whiteorbs]

Mine are crossed over and linked together like a horse shoe. Would that cause a problem?

So it's consistant. I can take it out for a ride and when I feel it start to loss power or umph I can turn the petcock off and after a little bit it recovers and runs normal . Then after a bit I have to turn the gas back on so it doesn't run out and the cycle continues. To much gas.

Scott where do you run those long vent tubes too?

[DaveBarbier]

The other two vents are in the center of the carb rack.

Is it absolutely necessary to have tubes running from those vents?

Only thing it does is prevent moisture and insects from getting in. Longer the tube, the less likely a praying mantis will make it's way in the carb bodies.

For what it's worth, mine is just about 6 inches long. The tube...I'm talking about the carb's tube here.


---
1978 Honda CB550K

[DaveBarbier]

Mine are crossed over and linked together like a horse shoe. Would that cause a problem?
...

Scott where do you run those long vent tubes too?

I think they should be vented to outside air. But if your overflow tubes aren't clogged, the bowls should still be venting enough.

You should route them with the overflow hoses down the back of the motor.

Edit: I'm just using my limited knowledge of the PD46C carbs to apply to this. Since Harrisuluv is around this area he can correct me if I'm wrong.

[Gene]

I had the same problem.  Make sure when setting your floats that you do not do it while the carbs are upside down on the table putting pressure on the float needle.  It has to be done with the rack on it's side and just touching the "spring".  I went round and round with it for a couple of weeks, finally got it right.  Be methodical, make sure the tangs aren't jacked up (nice and flat), make sure your jets are in correctly, make sure the brass for the float needle is INSTALLED ALL THE WAY - if it's not flush with the rest, you could have one carb acting up.

Sorry for the long sentence, my English teachers would beat me.  But, all I'm saying is - go over it again.  Also, make sure your fuel is clean.  Blow out the jets and the float valves with compressed air.

I swear, it'll get there eventually.  And I'm a total hack.

[HondaMan]

The bowl vents are VITAL to operation above 3500 RPM.
Without them drawing still, quiet air from behind the airbox (which is where they should end) the float bowls do not have enough high-pressure air to push the fuel up the jets. That's how these tiny carbs work: the faster-moving air in their throats cause a low-pressure area over the jet(s) and the higher pressure in the bowl(s) then push the fuel up those jets. There is an intermediate air-pressure zone at the bell mouth of the carb where the airbox fits: this in-between pressure feeds to the emulsifier tubes (those tiny holes in the brass tube above the jet) and bubbles the fuel as if rises through there enroute to the throat.

At hiway speeds, it is even better if you drill 2 small holes into the lower half of the airbox and snugly fit them in (as shown in my book, but that's a CB750 book) to receive the most still air possible at speed.

[Gene]

Also, I didn't have to do this but I've read about it.  Make sure the needles are positioned correctly re: the "slots" at the top.  Maybe one is different from the rest so it's not closing all the way?

[78whiteorbs]

You know a thought just occured to me. I hate to admit it but I dont think I pulled and cleaned my emulsion tubes  .
I did my cb350f and they were totally clogged and it got me to thinking and I dont recall doing these...this could be an issue causing a rich mixture and fouling plugs...when riding as I discribed that  by turning the fuel off it would  recovering because the lack of gas it causing enough leanness to clean some carbon off the plugs and actually have some proper combustion ...I am gonna do that tomorrow and see what happens.  The overflow vents are not puking and the clear tube method shows adequate range in fuel level at least at a standstill for a few minutes (havent tried longer) . This gives me hope and shames me at the same time!

[Scott S]

 As others have mentioned:

 Yes, the tubes need to be vented to the atmosphere, nit linked together.

 The carbs should be on their sides, slightly tilted back, with the weight of the floats just touching when setting float height.

 The emulsion tubes should be pulled, but they effect more mid-range operation. It might feel sluggish or run a little rich, but that shouldn't foul the plugs in such a short time like you're experiencing.

 You mentioned earlier in the thread about having not adjusted the valves. Did you ever do that? Have you use a vacuum gauge to sync the carbs?

[jmelche2]

Also...if you're going to pull the carbs again, replace the intake O-rings.  They are inexpensive and yours are probably hard as a rock.