Topic: How do you change the needle jets?

[Patrick]

Never one to leave well enough alone, as my CB750 K5 has been running just fine pretty much all summer, I happened upon some new needle jet sets. I've never changed the needle jets and I figured new has got to be better than the possibly 31-year-old jets in my carbs. Besides, here in Central Texas the really pleasant riding season is just starting and I want the bike in the best possible running condition. Anyway, after stripping the carbs all the way down I realized I have no idea how to remove the needle jets themselves. Now, I could do what  usually do - start hitting stuff until something falls out or off - but I figure I've pretty much lived a charmed life using that technique and one of these times it just might not work. Besides, my hammer is too big for the throat of the carb. So I'm up for something new. Like maybe asking y'all how to do it the right way.

What the correct way to remove these? Stick a punch down the hole and wale away, or grab from the bottom and twist with visegrips? I don't care about the old jets, but I would like to preserve the carb bodies - unlike thata horrible incident a couple years ago that involved a dirt bike carb, a drill and possibly one too many beers. Or one too few. It was ugly. Even my dog cried when she saw what I had done.

I am open to suggestions.

As always, thanks in advance.

Patrick

[Sam Green Racing]

Patrick, They just screw in I think.

Have your new ones not got a thread on them ?

Sam.

[heffay]

pretty sure sam's got it... shine a flashlight down there and see if they don't have a flathead screw notch on the top of them.  if they haven't been removed in a while they might be tricky.  DON'T STRIP THEM.  if you don't have a flathead screwdriver that fits the slot well... go buy one that does.

my two cents 

[Patrick]

Nope, no slot and the new ones don't have a thread. They have a wider ring about halfway down that looks like it would press in. That's why I was thinking maybe a punch would be the tool to use. Getting the new ones in, if that is the case, poses another issue altogether since there is no straight shot from the bottom to hit them with a punch, except up the shaft where the main jet screws in. And I really don't want to hit the new jets with anything as hard or harder than the brass they are made of. A wooden dowel, maybe?

I don't want to use force unless someone tells me that's the way to go.....

Patrick

[mrbreeze]

You have to unscrew the cap on top of the carb and pull the slide out.The needle is held in place by 2 screws under the slide.They are kinda tricky to get to.Make sure the screwdriver you use fits the screw well cause you DON'T want to strip the head on those screws. Being that your bike was running good before,leave the clip in the same groove of the needle as before.Hope this helps ya out.

[heffay]

shows how much we know... eh sam?

[jsaab2748]

unscrew the main jet and emulsifier tube as an assy. Look in the hole once you've removed previously mentioned part, and
tap the needle jet out from the bottom (float bowl side) upwards and out thru the floor of the carb  using a 5/16' pice of wooden dowel rod sharpened in apencil sharpner.

[heffay]

needle jets not jet needles

[Patrick]

Thanks everybody. That's what I love about this board. Quick and valuable information. Instant gratification. And thanks, Jsaab. I realized after I read your reply that I hadn't even considered which direction to hit them. I would have defaulted to the top and I would likely have made my dog cry again. She's getting too old to be that emotional. And when she is, the dogs next door laugh at her. Stupid chihuahuas.

I'll give it a try. I assume I tap them back in the same way, right?

Patrick

[mrbreeze]

Are you talking about the needle or the jet? the jet just unscrews if its a K5. The needle is how I described before.

[techy5025]

.....and then prepare to resync your carbs. 

Jim

[medic09]

Stupid chihuahuas.

If I had little rats next door, I think I'd let my dog(s) eat 'em.  Didn't know they allowed those things in Central TX (the Hill Country, by any chance?).

If you're out for a ride, stop at my favorite swimming hole on the Guadalupe for me... 

[Sam Green Racing]

shows how much we know... eh sam?

 

I would hang on m8 till someone comes on line that might know what your talking about.

Don't mess up, it could be costley

Sam.

[Patrick]

I live just north of Austin, Medic, and I likely have swum in your favorite swimming hole. I love the Guadalupe. I've spent a good deal of time there. Perenially cool water, cold enough to keep the beer drinkable, even when it's 110 degrees in August.

My last dog had an issue with one of the chihuahuas that lived next door. Lived, past tense. That annoying little rodent dog was yapping away, like the foul creature that it was, and Jazzy, my late, lamented overly protective black Lab, decided that enough was enough. Jazzy didn't eat the nasty little creature. But she did jump the fence and bite it practically in half. It died on the spot. I wasn't sure whether to thrash her or hug her. The neighbor wife was mighty upset. The husband, several days later, very quietly thanked me and gave Jazzy the bone from a t-bone while we built a higher fence. I miss that old girl. She was unrestrained by inhibition.

Jsaab was describing my dilemma very well. That is the needle jet I referring to - the jet that the jet needle slides through down into the emulsifier tube. I'll rap it lightly and if it doesn't move I'll stop.

Patrick

[mrbreeze]

Man ...I would sure like to use that black lab right now. My next door neighbors have a small mutt lookin dog that barks his ass off every time I step into my backyard.The damn dog barks at the wind!!!! I hate calling cops because it then turns into a retalliation kinda thing. But if I had a dog over visiting that would jump the fence and eat that worthless piece of #$%* dog for lunch....I would give him T bone dinners for life.
On the subject of your jets,the Early jets screw in (76 & below). The 77 & 78's are pressed in.

[Jerry Rxman Griffin aka MuthaF'er]

OK guys, these are not main jets or needles but rather the needle's "jet". Confusing, huh?! The needle actually slides in and out of this "jet". It does not come with your standard rebuild kit. It comes with the needle kit. No threads. No screw driver slot. Most guys probably are not aware they exist. JSaab wins round 1.

ps If anyone has a needle kit 16012-392-004 to spare I have 3 sets but need one more

pps Patrick, keep me updated on your dog and how you actually perform this. I'd rather you screw up first.   

ppps Sam & Hef, I don't know about you guys.........................................................

[mrbreeze]

OK....this is new to me.Didn't realize there was anything else in there.Why the hell wouldn't this be part of a carb kit?

[jsaab2748]

UPDATE!!!!!!!!!.................the needle jet is pressed out DOWNWARD thru the carb floor AND OUT OF the carb
thru the emulsifier tube hole (bowl end of carb.) after removal of the emulsifier/main jet asssy.  To do this you need to unscrew the ring on top of the carb and remove the top cover along with the throttle valve (The "sliding sleeve"), after which you'll be able to get a straight shot downward at the jet itself. Sorry to confuse with my first post, as it describes the proceedure BACKWARDS. Hope you read this in time before attempting and sorry that I dropped my d&%K in the dirt on this one

[Sam Green Racing]

Thanks for that guys, ya live and learn.

With the CR, we never had to go down that path as the donor bike came with a prity sweet runing motor.

We put it on the dyno and the operator synked the carbs.

The following year we replaced the stock carbs with the CR specials.

All the Keihin carbs I have worked on in the past have had the needle jet actualy in the emulsifier tube, just a tapered hole.

Thanks guys, Sam.

[eurban]

Are you going to replace your main jet needles at the same time you replace the needle jets?  Can't really see the advantage of replacing one an not the other.  In fact it may accelerate the wear of the main jet needles .   When I purchased a new set of needles for my 78 carbs they came with new needle jets as well.  On the 77/78 carbs anyways, the needle jets are pressed out from above.  Hope this helps. 

[Jonesy]

Go to this site. Every step is photographed: http://www.salocal.com/sohc/tech/carb/carb.htm

[Patrick]

God I love stuff you can fix by hitting it with a hammer.

RXmangriff - it was just as simple as described. Instead of 5/8 dowel, however, I used 1/4 hardwood dowel, since that's what the hardware store had handy. I used hardwood because I didn't know how hard I was going to have to hit it and I didn't want to deal with random pine wood shards getting into stuff. The thinner dowel was the perfect size. When you do it I suggest you taper the end of the dowel a bit. I found that the jets didn't just pop out when they loosened and had to be pushed a bit. If you don't taper it a bit the dowel gets too wide too quick. But they came out with light tapping. Then you tap the new ones in up through the emulsifier tube. Easy. And, from the looks of the corroded, pitted condition of the first two jets (I haven't done the second two - they are stilling soaking in carb cleaner) I now understand why my air screws were all adjusted differently, ranging from 1 1/4 turns out to almost 4 turns out to make all the plugs burn tan and the bike idle smoothly. I'm betting they were the originals. This should help.

And Eurban, the needle jet kits came with new jets, needles and circlips, so it replaces the whole needle assembly.

Ready for another 31 years on the road. Up in heaven, where all creatures that kill chihuahuas go, Jazzy is smiling.

Patrick

[pelicanwheel]

timely topic for me (as many are these days as I put together my restoration project).  I've been doing the carbs the last few days.  Here's what I've learned:

1) my local powder coater did a fabulous job on every painted part on the bike, less the engine cases.  Inexpensively.  He didn't want to do the carbs for various reasons, but I talked him into it anyway.  These were carbs with only 10,000 miles.  When I say "were", its because they are junk now.  The paint came out terribly bad and the screw on caps are stuck.  I tried to remove them but the force to do it deformed the verticle chamber on one.  The paint isn't that bad really, just not good enough for the caliber of restoration I'm doing.  If anyone is interested in three decent looking, "chrome colored" '76 cb750 carbs (without the guts), and one that the tube is slightly bent (maybe can be made round again), they are yours for free (minus postage).  First come first saved.  I can provide pics.

2)  The number 2 and 3 carbs is different in that there appears to be jets of some sort on the roof of the float bowl chamber - in 1 and 4 there is one jet eachs, but in 2-3 there are two.  I think these passages are for the distribution of gas across the four carbs.

3)  I soaked the carbs in chem dip over night and they came out coated in a blackish slime.  It rinsed off easy enough, but I get the feeling that the protective coating that may have been on the bodies are gone now.  Also, the brass parts turned black and doesn't rinse off as well.  I dont know why.  Lastly, the distribution "t"s turned completely black!!  Yikes.

I've painted two of the bodies with the duplicolor 1615 high temp spray paint and they look great.  I'm nervous about durablillity though.  I'm considering using automotive primer and paint.

Stay tuned!

Pelican

[Jerry Rxman Griffin aka MuthaF'er]

Our stock 750 carbs ALL have a 28mm opening in the carb for the air to enter and pass through. Your bike has an 836 kit with ported and polished head. I think what your guy was referring to was going with a larger carb. ie a 29mm or a 31mm. Your larger displacement will flow more air. Your ported and polished head will flow more air. More air means you can pump more gas. More air and more gas mean bigger bang. Bigger band means more power. With what you have done to your engine, it deserves bigger carbs to really turn it loose. Not really frustrating, just more $$$ & more HP. Hope this makes sense.

[mrbreeze]

Well....I learned something new today.When I went through my carbs, I didn't change the needle jet because I didn't know it existed.I also kept the stock needle.Essentially,I am running fairly fresh rebuilt carbs with 31 year old jet needles & needle jets! I purchased my kits from Dennis Kirk (K & L , I believe was the brand).The needles were in the kit but not the needle jets. I used the originals because someone here mentioned the ones in the kit had a different taper. So I wonder why they give you needles just to stick in the old jet. doesn't make any sense. So you say that buying a needle kit is the way to get the needle jets? What is the best route to go....please don't tell me the dealership cause I know thats going to be crazy expensive. Where has anyone picked these up for good quality & price ? My bike doesn't run bad but now I'm wondering if it could be even better.What kind of problems could I be having with worn out needle & jet? Some people here wondered why my bike runs best with 138 mains & needle  on 2nd clip from top. I read in the solacal post that renewing  needle & jet made it run better and easier to tune.Any and all replies welcome on this subject.