Topic: That's why they press in the slow jets....

[Cvillechopper]

OK, I'm not new to the motorcycle maintenance scene, but sometimes I feel like it.  Today I figured out why the guys (or gals for the pc folk) used press-in jets on the cb750K 8 .  So idiots like me don't end up drilling them out about 4 times their size while trying to clean them.  Yeh, hurts to hear, doesn't it.  Soaked them for a few hours then got an old spring and ground down the end into a point.  I figured the holes on either end of the jet is larger than the spring (straight portion) so I couldn't do any damage.  Well, after the 3rd one I started to wonder why it was taking so much effort to get the gunk out but figured they just might be that bad since they've been sitting for a few years.  On the forth I noticed the small brass shavings.  I've installed them as is and got the bike running, but she's got gas to spare for sure.  I don't think any amount of adjustment will bring her anywhere close to clean.  Any suggestions as to where I can order slow jets for a 78 cb750 K?  I've seen 69 through 76 and 79 up, but not 77 or 78.  Here's hoping I didn't just set my project back another month or 2 looking for jets. 
(hangs head in shame)

[eldar]

I have not seen ANYTHING for slows for the 78k. You might be able to make some using brass or maybe copper tube. Otherwise maybe someone has something else to offer. The only other Idea that just popped into my head is that you might be able to put threads into the carb bodies to use screw in jets.

[Terry in Australia]

Well those holes are tiny! I had one blocked on my 77 F2, it was so bad I had to replace it, I couldn't unblock it. How many do you need, I might have some spares? Cheers, Terry.

[Cvillechopper]

All four are shot.  Let me know if you have some and how much you want for them.  I would appreciate it greatly.
Thanks
James

[Joe Danger]

I seem to recall a post on the old site that recommended a particular jet that motorcyclecarbs.com sells.

The trick was, you had to turn it on a very small lathe, or use a soft vise and file, to take off the threads.  I have #42s in mine, I'd suggest any slow jet you can find that has a reasonably similar shape and a .42mm aperture.  (Or whatever your particular desire is.)

It won't be fun, but the other option is a new rack of older carbs.  There's a bit of munging to get the rubbers on, but we are hardy and inventive souls here.

[Cvillechopper]

I thought about new carbs right off, but have been told that the 77/78 carbs were better, just harder to find parts for.  Anyone know if this is true or just someone buying into the Honda sales schpiel from those days?

Also, does the emulsion tube separate from the jet or is it one piece?  I could probably make something to work if I can separate the 2.

I'll try that website first.  Maybe I'll get lucky.

[bryanj]

If you find anybody selling those jets post it on hear cos i been trying for years

[carpy]

Hey Gang
Have you tried SUDCO?
They are about 45 mins from me and are a main importer of Kehien carbs, they have  over 15 sandcasts there and more 750's I have ever seen in one place, more than i have owned and I have owned over 100 CB750's in 5 years.
I think they have a website but need to check it out and see, as i just drop in there.
carpy

[dusterdude]

carpy!!!!,you`re alive!!!!!

[Cvillechopper]

Carpy, I found the website for the place you're talking about and e-mailed them to see if they can order teh jets.  Of course they're not listed with the rest of the Keihin jets, but here's hoping.  I also just thought about something while looking at a chart of the throttle range effectiveness of different adjustments to your carbs.  It seems that the slow jet and the pilot screw effect the same range and from what I've seen/ read the pilot screw is downstream from the slow jet...  If this is the case, would it be possible to use the pilot screw to lean it out enough?  I'll try just about anything once...

[TwoTired]

It seems that the slow jet and the pilot screw effect the same range and from what I've seen/ read the pilot screw is downstream from the slow jet...  If this is the case, would it be possible to use the pilot screw to lean it out enough? 

It would seem like it.  Possible stumbling block.  Are the slow jet orifices now of uniform size?  If not, each idle mixture screw will have its own unique setting and may be quite sensitive.

I think if you yank out the pilot jet, you will find it does indeed have an emulsion tube attached as part of it.  You will also probably find that the emulsion tube holes are plugged too, which may be contributing to your rich slow mixture.

A thought.  I haven't tried it but..  Couldn't the body of the carbs be tapped to accept a screw in jet?  Like the N424-22-XXX  found at :
http://www.sudco.com/keihinjets.html

You might need to grind down a tap to make it a bottoming type.

Cheers,

[eldar]

Thats what I was thinking. Maybe tap the carbs to accept screw-in slow jets. I think that might be easier than getting slows and machining the threads off.

[Cvillechopper]

I just thought of something else.  Would making a plug for the bottom end of the jet and getting a jewlers bit to drill the proper size hole work or is there a reason the diaphram was half way up the tube?

[eldar]

I think what might happen is that either the pressure of air in the emultion tubes would cause the gas to not be drawn up into the jet or the jet would not meter correctly and fuel would load up in the tube then get sucked into the engine causing backfires and fouling.

[TwoTired]

I just thought of something else.  Would making a plug for the bottom end of the jet and getting a jewlers bit to drill the proper size hole work or is there a reason the diaphram was half way up the tube?

Well, yes.  Has to do with laminar flow of fluids and retension of fluid in the emulsion tube.  I can explain if you think it will help.  But, it's wordy and technical and bores some people.

BTW, it's an orifice, not a diaghram.  Technospeak, you know.

Anyway, I would plug and redrill only if there was no other way.  I believe some aspect of performance will be lost.  FYI twist drills leave jagged, irregular holes, whereas reamers leave smooth round ones.
Cheers,

[Cvillechopper]

Well, I tried the "tighten down the mixture screw and pray" method, but still looks like a diesel rig.  There's a place that says they have the slow jets for the CBX style carbs but they needed my measurements.  I'm thinking they don't know about the press-in thing.  I sent the dimensions in great detail including the taper length and steps and mentioned once again about them being press-in so hopefully they'll have something that works.  Anyone know about the CBX jets and compatability?

Also, just in case you were wondering, the measurements are as follows:
The large part of the jet is 14mm long x 5mm od
The seat for the press-in part is 4mm long tapered from 4.5mm to 4.25mm to 3mm in stages
the emulsion tube is 9mm long x 3mm od. 
Total length 28mm
Inside diameter is approximately 1.75mm other than the orifice (see, I do learn)

[TwoTired]

CBX carbs are CV types and the fuel jets are all screw in types.  But, I don't remember if the slows had emulsion tubes on them.

From your dimensions, it sure seems like the one from the Sudco site might work.
N424-22-XXX
For some Honda PE Series carbs. Sizes #35-#80.

Why don't you call them to see if other dimensions match up?

Cheers,

[Terry in Australia]

All four are shot.  Let me know if you have some and how much you want for them.  I would appreciate it greatly.
Thanks
James

I'll take a look tonight and let you know James, the fee will be a porno mag or a bike mag (no dirtbikes and no gay mags though, I do have some standards! Cheers, Terry.

[Cvillechopper]

I'd say at least one of each, maybe my whole stash plus a new one....

[Terry in Australia]

I'd say at least one of each, maybe my whole stash plus a new one....

Well for all that I'll just send ya my carbs! Ha ha, Cheers, Terry.

[Cvillechopper]

Terry, send me an e-mail with your addy and I'll send you some mags just for the offer.  As for the jets... I got WAY lucky today.  Went to the local dealer/ shop for a set of points and saw that they had a plastic bin with some jets in it behind the counter.  Went straight home and pulled my wrecked jets and took one in to see if what they had might match up.  I've now got a set of #38 screw-in jets the exact same length and width.  The amazing thing is that they acted just like self-taping screws into the carb body and she idles fairly clean although I've got a little top-end noise that I'll have to look into.  Tomorrow after work I'll see if I can get her dialed in.  Here's hoping that everything comes together and I can get a test drive in on Saturday.

cvillechopper@earthlink.net

[Cvillechopper]

Alright.  The jets I got from the dealer work great.  Idle is fairly smooth.  Now when I give her a quick pop of the throttle I get an immediate response, but then a backfire or pop depending on her mood.  Timing is dead on and the valve clearances have been checked twice.  I did notice while the rocker cover was off that when I have the crank and TDC 1.4, the cam is just a hair off from perfectly lined up with the notches up top.  Looks like about .5 mm at most. 
I've got 110 mains in and 38 slows with the bowl height at about 14.5.  Not being all that great with carbs(evidenced by my honing the slows to 210s )  I have spent about 2 hours with the girl running at op temp and fiddling with the screw settings to no avail.  I really can't distinguish slight rpm diffs and my gauge (hooked up for tuning, not mounted) doesn't really notice 50rpm changes.  I was wondering if anyone could point me in the right direction.  I've read all posts on tuning and haven't been able to make them work for me yet. 
BTW, thanks all for the help so far and any help coming.
James

[TwoTired]

Is the only complaint the backfire/pop at throttle let off?

Is your exhaust system sealed up well?

Are the plug deposits even across the four plugs and a nice color?

Are you running a fan on the motor to keep it cool while tuning?

Do the manometers show even draw for all carbs?

What's your air filter set up?

[Cvillechopper]

Wow, didn't even think about the temp. 

Only complaint is the backfire/pop at let off, yep.  No smoke, fairly level idle.
I didn't have a fan on while working on her.  I'll make sure to get one for tomorrow. 

I know the exhaust has a little leakage around a weld or 2 that I can seal up.  Wasn't aware that the pin-hole leak would make that much or a diff. 

Don't have a manometer but will pick one up if the local shop has one tomorrow prior to starting work on the girl. 

So far, I've only run her withour anything on the intake.  Was planning on putting stacks on and figured that made little difference.  That not the case? 

With the bike supposedly running great when she was parked before I got her I didn't think the synch would be necessary.  Chalk that one up to a youngster getting anxious and hasty. 

I'll update once I get my head outta my ass and do things the right way.  Thanks for asking me the simple questions that I should have known to answer myself   That's why I love this place.

James

[Terry in Australia]

G'Day James, without the airbox in place it'll run lean, as the airbox adds a bit of "choke". You'll need to experiment with your needle height (up for rich, down for lean) or just keep working on bigger main jets, whichever's easist. Those carbs were set lean in the factory to help with emission laws in the US, that's why they fitted accellerator pumps to get rid of the flat spots when you crack open the throttle. Without the airbox, they'll run really lean.

Check all your rubber mainfolds for air leaks, just spray some WD40 around the carbs while it's running, that'll tell you if they're leaking. Did you want a copy of the K8/F3 manual on CD? I'm sending one to Terry Quail on Monday, so it's no biggie to copy another one? Cheers, Terry.

[TwoTired]

I know the exhaust has a little leakage around a weld or 2 that I can seal up.  Wasn't aware that the pin-hole leak would make that much or a diff. 

If your exhaust gasses have fuel in them, as they might during decel, the introduction of air into the exhaust can add enough oxygen to light off the exhaust mixture.  POP

Don't have a manometer but will pick one up if the local shop has one tomorrow prior to starting work on the girl. 

Make sure you get the addapters for the four intake runner plugs, too.

So far, I've only run her withour anything on the intake.  Was planning on putting stacks on and figured that made little difference.  That not the case? 

If the stacks have any filtration restriction, they add a bit "choke" as Terry said.  Theoreticaly, the stacks also should smooth out the intake flow and reduce turbulent flow.  (Isn't that why your putting them on?)  As the turbulence pressure points can move around within the carb bore with different velocities, it can change fine tune fuel flow.  So, fine tuning should be performed with the bike in road configuration.

With the bike supposedly running great when she was parked before I got her I didn't think the synch would be necessary. 

 Two things.  One persons "running great" and another persons, can be different.  Further, the carbs are mechanically slaved, but there can be mechanical wear or vibration drift with operation.  Did you take out the slides during the cleaning procedure?

Thanks for asking me the simple questions that I should have known to answer myself  

You can count on me for the simple questions. 

[yoomit]

ok, so i can't tell by the posts here, so i'm going to ask.
is it suppose to be hollow all the way thru the length if the 77-78 slow jet?  i'm assuming yes, because when i look thru one of them i can see a crack of light shining thru.  the other 3 are completely dark. 
i'm assuming this means they are way clogged.

i tried taking a piece of safety wire and twisting it around inside...but nothing is even loosening up in there.  am i grinding brass?!

i'm soaking them overnight, but i have a bad feeling that stuff is caked on in there.
that being the case, am i completely screwed?  it sounds like these slow jets aren't even available to buy anymore...not even from the dealership??!

anyone try boiling them in hot water...does it help to loosen up the clogging?  will it warp the brass?
need help!

- M

[theunrulychef]

Yoomit, if you have an air compressor, try soaking them in carb cleaner & blowing them out (careful not to blow any cleaner on your face  ).  Might help to loosen up the crud.

-Jay in Philly

PS - Boiling them shouldn't warp the brass.  You might mess them up if you used a torch on them though.

[yoomit]

ok, i've got 3 of the 4 jets cleaned out.  just so i'm sure i've got it right...the hole INSIDE the jet is much smaller in diamater than the openings on either end.  is that correct?  or are these things still clogged.  i seem to recall that there's an inner diaphragm of some sorts. 

not having known about this inner thing prior to my first time cleaning it, i wonder if i muffed it up by trying to jam a thicker safety wire thru it.  it was narrow enough to go thru either end's opening...but didn't realize at the time that the inside got narrower.  f*ck.
i just figured that what was stopping the wire from going all the way thru was more clogged gunk...now i realize it was the inner thingamabob.

question:  IF the 3 i have are sufficiently cleaned, you think the bike will idle and run well even tho the 4th one is still clogged?

last question:  are these jets absolutely unavailable anywhere.  best scenario would be to just get new ones, but i keep reading how rare they are to find.
thanks!
- M

[eldar]

VERY hard to find. You will need to search on it but a memeber here named buffo, installed screw in slows. He gently tapped the carbs and screwed some in.

[fang]

I just hopped on to this discussion, but here is a simple solution for your "drilled out" slow jets:
place a dab of solder on the jets and then re-drill them with some precision micro-drills.   Something like THIS or THIS.

When I was in Peru I didn't have many options as far as obtaining spare parts so we frequently had to evoke the god of 3rd-World auto repair.  Things are different down there and you do all kinds of things to keep old vehicles running, including bizarre carb swaps, and anything else you can imagine....

If you can get a micro drill set (and I think every guy should have two -- because the bits often break) it is an easy fix.  If you have access to an unmolested carb then it will be even easier to match up the correct size.

Best of luck!

Peace and grease
-fang

[kettlesd]

Holy Crap -  alot of responses on this thread!!!!!!

Of the subject of filling in the slowjets with solder and re-drilling them out - i really wouldn't recommend it for a few reasons. First of all if you if you look at one of the jets carefully you will see that it is not a straight tube. The restriciton narrows in the middle by a few thousands of an inch somewhat like a gentle hourglass shape (like a Bernouli tube to those in the aerodynamic world - to assist in velocity and atomization of the fuel). Secondly, i dont know about your drill press, but even on my brand spanking new press the spindle still has enough vibration to it that i would not bet money on a perfectly symmetrical .013" hole going straight down!!!

Get some jets off ebay or the boneyard. I'm sure you know the jets can be removed carrefully with a pair of slipjoint pliers (NOT vise-grips!!!!!!!! Using the slip-joints they will come out easily by rotating & pulling gently and u can have a better "feel" for the soft brass and not crush the tube).

The jets on my K8 were so gummed when i brought it home that i could not even blow compressed air through them. Soaked them over night in carb cleaner and then carefully worked them free with a guitar string. I know everyone abhors using wire to clean jets, but guitar strings come in thousands of an inch graduations. Use one that is a couple thou smaller diameter than the hole you are trying to clean. I used a 0.11" "B" string to help clean the 0.13" slowjet on mine. Spin the wire through the obstruction between your fingers like a drill and dont jerk it in and out and you will not distort the jet. Finish the job by blowing them out with compressed air.

[yoomit]

ok, so that answers one of my questions...it's definitely narrowers toward the middle of the jet. 
and it's likely the 3 i have are gunk-free. 

now to the last remaining jet...playing out the scenario that i won't be able to remove the gunk, nor find a replacement, how well will the bike run if i run 3 clean + 1 clogged?

[bryanj]

It wont run on the one clogged

[yoomit]

   well that sux.

[fang]

FYI, when you solder and fill a jet, you hand drill them.  micro drill bits sometimes come with a simple hand chuck.  I am aware thatthey taper, but if they are buggered up the "fill and drill" method is worth a try.  In the past I have done this with main jets with great success, but never any as small as our bike's slow jets.

Good luck!
peace and grease
-fang

[Terry in Australia]

  well that sux.

Well yeah, but there aren't too many things on your bike that you don't need, or they wouldn't be there............. 

[yoomit]

GUITAR STRING!!!!
thanks, kettlesd...it worked beautifully!!
sticking these bad boys back in this weekend...hoping for a long afternoon ride!
- M

[dusterdude]

FYI, when you solder and fill a jet, you hand drill them.  micro drill bits sometimes come with a simple hand chuck.  I am aware thatthey taper, but if they are buggered up the "fill and drill" method is worth a try.  In the past I have done this with main jets with great success, but never any as small as our bike's slow jets.

Good luck!
peace and grease
-fang

its called a pin vise.