Author Topic: cb550 still fouling plugs (Read 8834 times)

78whiteorbs · « **Reply #25 on:** April 20, 2015, 09:00:29 PM »

Ok so did everything on my list and since all bowls were measuring even with the gasket level which theoretically would be flooding the carbs I changed the floats to 26mm. Also had a look at all the idle jets and they va re 38 keihin brass and don't look to have been drill out or anything compared to all my spares. Now I went to change out the main jet orings and didn't feel happy with how they are fitting. They wiggle a little loose like a tooth ready to be pulled. I know the pressure from the spring clip in the bowl should add some tension to make the seal but I am suspicious of this here. I went reading and came across this:
http://forums.sohc4.net/index.php/topic,143159.25.html

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. I think I just assumed where the tale tell signs of plier marks were the sides sticking out but could use some confirmation here... what side sticks out towards the carb bowl?bbackwards jets could be a problem....

mrfish2 · « **Reply #26 on:** April 20, 2015, 09:02:47 PM »

The side with the number stamped on it should stick out into the bowl

78whiteorbs · « **Reply #27 on:** April 20, 2015, 09:13:10 PM »

Well the were in correct then.hopefully I had the correct size orings. They seem like they may be a little small. I got them from four into 1 when I got my new needle valves and seats.

Hopefully it was just to high a fuel level flooding them out. We'll see tomorrow.

harisuluv · « **Reply #28 on:** April 20, 2015, 09:23:23 PM »

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 · « **Reply #29 on:** April 20, 2015, 09:34:01 PM »

Quote from: harisuluv on April 20, 2015, 09:23:23 PM

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 · « **Reply #30 on:** April 21, 2015, 03:49:23 AM »

Quote from: 78whiteorbs on April 20, 2015, 09:00:29 PM

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 · « **Reply #31 on:** April 22, 2015, 09:59:18 AM »

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 · « **Reply #32 on:** April 22, 2015, 10:15:53 AM »

78whiteorbs please post some pictures.

78whiteorbs · « **Reply #33 on:** April 22, 2015, 10:17:43 AM »

Will do

78whiteorbs · « **Reply #34 on:** April 22, 2015, 10:41:55 AM »

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 · « **Reply #35 on:** April 22, 2015, 11:13:27 AM »

Quote from: 78whiteorbs on April 22, 2015, 09:59:18 AM

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 · « **Reply #36 on:** April 22, 2015, 11:16:58 AM »

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 · « **Reply #37 on:** April 22, 2015, 12:50:10 PM »

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 · « **Reply #38 on:** April 22, 2015, 12:57:32 PM »

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 · « **Reply #39 on:** April 22, 2015, 01:21:09 PM »

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 · « **Reply #40 on:** April 22, 2015, 01:24:19 PM »

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 · « **Reply #41 on:** April 22, 2015, 01:30:55 PM »

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 · « **Reply #42 on:** April 22, 2015, 05:34:54 PM »

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

mrfish2 · « **Reply #43 on:** April 22, 2015, 06:09:06 PM »

Quote from: Scott S on April 22, 2015, 05:34:54 PM

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

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

78whiteorbs · « **Reply #44 on:** April 22, 2015, 07:13:05 PM »

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 · « **Reply #45 on:** April 22, 2015, 07:24:26 PM »

Quote from: mrfish2 on April 22, 2015, 06:09:06 PM

Quote from: Scott S on April 22, 2015, 05:34:54 PM
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 · « **Reply #46 on:** April 22, 2015, 07:40:42 PM »

Quote from: 78whiteorbs on April 22, 2015, 07:13:05 PM

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 · « **Reply #47 on:** April 22, 2015, 07:51:44 PM »

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 · « **Reply #48 on:** April 22, 2015, 07:54:19 PM »

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 · « **Reply #49 on:** April 22, 2015, 07:54:55 PM »

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?

News:

Author Topic: cb550 still fouling plugs (Read 8834 times)

DH

DH