Topic: 78 750K8 slow jets

[jlfcopter]

Hi all, new person here.  I checked all posts for advice.  I am cleaning my carbs and see that some advise to "pull" the slow jets. These are the tubes next to the main jets? How are these pulled? If you use a pliers, do you twist and pull?  I am looking for techniques I guess.  I would hate to damage them.  I bought this bike new and it has been super!  Never cleaned the carbs before, but have noticed a bit of rough idling and not keeping steady slow speed(10-20?) the past few years, it jerks a bit. The carbs look pretty good inside the bowls and a bit of crud on the slides.  I also read that they are dipped and soaked. Some recommend Simple green? then spayed with carb cleaner inside through all orifices and then compressed air. Thanks for any advice.

[sandcastcb750]

I bought my 1978 cb750 in 1981 with 1500 miles. You're lucky. My carbs quit working in 1987 with 11,000 miles. I gave up and went with earlier carbs as those K8 emission press fit stuff is a bear. My neighbors K7 has been a problem too.

[jdigga]

Yes, they're the smaller ones next to the main jets that should be threaded but aren't.  

You definitely have to pull them to get them completely clean.  I used a pair of vice grips with a towel folded a few times over to protect the jets (others have used a small piece of leather or something similar to give you some cushion + grip.  A little twist will loosen them, then be sure to pull straight out.  Also make sure they go straight back in.  I believe there's also an o-ring inside you don't want to lose.

[pddpimp]

Yep, you just have to grab them with a pliers or visegrip. Don't worry too much about scratching them, it doesn't effect a thing, other than the way they look. Just twist and pull, don't wiggle around too much or it may effect the bore that the jet is pressed into. I don't remember an oring being inside of there, but if there is, just remember to put it back in. These jets being plugged is 90% of the time the problem at low RPMs. Clean out all of the side holes, I believe there are 6 of them. And then clean out the hole that runs threw the center of the jet. Becareful with this, you don't want to mess up the hole size. I have soaked them in the past and used a fine wire, such as a peice of speaker wire, to loosen up the build up. The blow them out with compressed air. CLean, clean, clean...Can't express it enough with the slow jets. Oh, an make sure you can see light threw the jets before you put them back in. And make sure that the holes look the same size. To reinstall them you can just tap them in with a hammer and a punch. It doesn't take much, so be careful.

Hope this will work for you, keep us posted.

[medic09]

I agree with pdd.  My slows now show teeth marks (despite the padding I used), but they work great.  CLEAN, CLEAN, CLEAN.  I used all the methods mentioned (except I have 'official' carb wire cleaners!  ).  Pad the top of the jet when you go to tap it in.  Gentle tap using a broad punch (you don't want to stretch the orifice).  I also don't recall any o-ring.  Just get it seated straight and firm.

Good luck!

[BobbyR]

I agree with pdd.  My slows now show teeth marks (despite the padding I used), but they work great.  CLEAN, CLEAN, CLEAN.  I used all the methods mentioned (except I have 'official' carb wire cleaners!  ).  Pad the top of the jet when you go to tap it in.  Gentle tap using a broad punch (you don't want to stretch the orifice).  I also don't recall any o-ring.  Just get it seated straight and firm.

Good luck!

It is as easy as everyone says. When you put them back press them back in a bit with your thumb for alignment and just gently tap them into place. Piece of cake really.

[eldar]

I dont remember an o-ring either. As for the carbs dying, that is probably poor maintenance. These carbs are very flexable and work very well. They just require a bit of a different technique than the earleir carbs do.

One thing to also work on, the accel pump. Pull it apart to make sure it is clean the diaphragm is not torn or ripped in anyway. Then put it back on and adjust the lever that actuates the pump rod. There should be something like a .008 gap. Then pull your fuel screws and clean that area. Put them in and set to 1.5 turns out if you are using the airbox and stock exhaust. Maybe 1.75 if using pods just as a starting point.

[jdigga]

I could have sworn there's a clear plastic o-ring inside, but I could very easily be mistaken as I only pulled the jets once.

+2 on the accelerator pump.  I don't think I addressed that fully until I had taken the carbs apart several times.

[medic09]

+3 on the accel pump!  Mine was *full* of brown gunk.  Amazed that it worked at all before I cleaned it.

[BobbyR]

+3 on the accel pump!  Mine was *full* of brown gunk.  Amazed that it worked at all before I cleaned it.

I second that.y accel pump is so full of stale fuel it was amazing.