Topic: carb issues on k6

[fartypants]

THE plugs on my cb750 k6 are getting sooted up vey quickly and the bike is obviously running to rich and it must be the carbs as i have run them on a k4 and they are doing the same on that bike, what is the needle clip pin setting , jet sizes ect, or any other ideas why this is happening and is there a quick fix
cheers
Andy

[Johnie]

This will give you the specs you needed:

http://www.motorcycleproject.com/motorcycle/text/specs.html

[lucky]

THE plugs on my cb750 k6 are getting sooted up vey quickly and the bike is obviously running to rich and it must be the carbs as i have run them on a k4 and they are doing the same on that bike, what is the needle clip pin setting , jet sizes ect, or any other ideas why this is happening and is there a quick fix
cheers
Andy

You are going to have to find out all the facts about your carbs. So you will need to take them off.
No stories just facts that you verify yourself.
Then report back.
EDIT:Idle jet size #40mm.
Main jet size #110mm.
EDIT: Needle clip position fourth from the top..
mixture screw one turn  out.
EDIT: Stock airbox.
EDIT:4 into 4 stock exhaust.

Make sure you remove the idle jets and hold them up to the light. Make sure you can see the hole.
Just squirting carb spray and calling it good is of little value.If the float needle has not been changed for years replace it.
Check the float levels with a float gauge or a steel ruler.

[fartypants]

I am going out to the garage now to take the carbs off and i will report back, the bike is on standard honda exhaust 4 into 4 and standard airbox.
cheers for all your help its really appreciated.

Andy

[fartypants]

here we go with the specs

main jet looks like 110
pilot unmarked
needle clip one up from needle taper end i think the middle setting is standard so would indicate a rich mixture being fed to the engine
standard exhaust and airbox
airscrew 1.5 they look like they have been replaced recently
float hight one at 23mand three at 24
all jets very clean and carbs clean
pilots being unmarked and new airscrews indicate carbs have been fettled with in the past

i hope this helps
cheers andy

[fartypants]

another pic of carbs

[Johnie]

Take a look at the top of the carb body. There will be a flat spot with a number like 657A or something stamped in there. That is the reference number you will use from the chart that I provided to get the carbs back to the OEM setting as far as the clip, jets and float. I can tell you now your floats are not set to spec at 23 or 24. They should be 26mm. You said you have 110 mains and according to the chart you should have 657A carbs. If that is the case then there should be #40 slow jets, needle clip in #4 position and air screw 1 turn out from lightly seated. By the way...welcome to the forum.

[Johnie]

One last item, when you set the floats keep in mind you do not put the carbs completely upside down to set them. The Honda service manual says to tip them on the side and angle them so the float needle just makes contact with the needle seat. That is where you take your measurement of 26mm. Here is a pic of a handy float gauge you can make to make it easier.

[harisuluv]

Odd that the pilots are unmarked.  You have a good start to go by and seems like most of the pertinent specs.  I will add that you mentioned they have obviously been into before, sometimes when people do this they clean them improperly with some kind of wire and can really alter the dimensions of the jet without the proper too to do prevent that.  Something to think about.

[fartypants]

Hi johnie and folks, i really appreciate the help ...the carbs have 657b on them and i take it that the needle is set correct at position 4, should i alter the needle hight to number 3 the middle setting and try that and see how i go, i do have an old set of k6 carbs in the shed that i might be able to get some parts from.

cheers
Andy

[harisuluv]

If I were you I wouldn't go first for the needle clip.  You have a stock setup and it is correctly in the stock position.  By the way, you said your bike was a k6 I believe and the stock jet for that is a 105 not a 110 which you say you have.  I would fix the float heights and then go back to stock jets and then see if that makes a difference.

[brewsky]

Air filter new or clean?

[Johnie]

Yup, per the chart above the 657B carbs should have the 105 mains. I would start there and get it back to OEM specs and set the floats at 26mm.

[GammaFlat]

Clean the port in the air intake side of the carburetor.  I have a K6 and HondaMan recommended I do this to resolve my "sooty plugs".  It did the trick.  I don't recall if I had 105's or 110's at the time.  I was largely stock then except for a 4-1 exhaust.  Here's a picture of an "E" string (I think) from a guitar with a "jog" bent into it to help clean the crap out of the port (rotate the wire to scrape the crud from the opening at the jet holder base).  The area you are really trying to clean is at the base of jet carrier "hole".  A small percentage of restriction here will cause sooty plugs.  See pictures below:

[lucky]

Odd that the pilots are unmarked.  You have a good start to go by and seems like most of the pertinent specs.  I will add that you mentioned they have obviously been into before, sometimes when people do this they clean them improperly with some kind of wire and can really alter the dimensions of the jet without the proper too to do prevent that.  Something to think about.

The pilot jets ARE marked.
Look on the sides near the bottom edge.
Not all 4 could be unmarked. Not unless it was on purpose.

[fartypants]

Hi , i have just found out that the carbs in my shed that came with the bike as a spare set are the original ones fitted to the bike new and are marked 086A but i believe they are the same spec as the 657b ones that are now fitted..looking inside them they are very dirty but the mains are marked 105 and the slow jets are 40, all the parts in these carbs are genuine factory originals including the slides and needles,  can i clean them up can i fit them to the 657b bodies including the slides and needles, oh and yes the air cleaner is new and the bike has new airbox and intake rubbers.

cheers
Andy

[fartypants]

Clean the port in the air intake side of the carburetor.  I have a K6 and HondaMan recommended I do this to resolve my "sooty plugs".  It did the trick.  I don't recall if I had 105's or 110's at the time.  I was largely stock then except for a 4-1 exhaust.  Here's a picture of an "E" string (I think) from a guitar with a "jog" bent into it to help clean the crap out of the port (rotate the wire to scrape the crud from the opening at the jet holder base).  The area you are really trying to clean is at the base of jet carrier "hole".  A small percentage of restriction here will cause sooty plugs.  See pictures below:

Thanks i am going to do this before i refit the carbs.