Topic: K8 Carbs

[mixstup]

Hi,Im new to the board...had a look through the posts but I am having trouble getting my new(old) 750K8 running right,Please advise what baseline jetting is needed for this model with a 4-1 pipe and K&N filters,have tried three sets of (clean) carbs and a bunch of jets.The best Ive got is centre needle pos,35 pilots,120 mains,air srcew 2 turns out.It wont run off choke,have checked the compression...120 psi on all 4 ,points checked,valve clearances good,Mystified and soon to turn to drink!Mick

[GammaFlat]

Don't underestimate drinking   Welcome.  I believe that factory jets on a K8 are 110s or 115s (I'll check). 

Understand that K8s are cold blooded.  In my experience, it takes a while to get them warmed up. 

Carb cleaning is a sort of religion or a right of passage you understand.  You'll get folks here on the forum that will ask you to clean them 3 times, click your heals and light incense before you post back  

I'll not ask you to click your heals...  One thing I would look for that is easy to overlook when you clean carbs is the airhorn that leads to the emulsifier tube.  It's on the airfilter side and sort a small brass fitting with a hole in it that is at 12 o'clock (on K7 and K8s) on each carb.  That leads to the emulsifier tube and allows the fuel coming in through the jet to mix with air.  If it is partially or completely obstructed, you'll have issues.  Thankfully, those "ports" on K7s and K8s are straight and easier to clean than on K6 and prior (the dang things take a 45 degree detour).  Remember that it is not good enough that the passage is "open"... it must be completely clear.  Partial blockages are not good. 

Emulsion tubes and jets must be very clean as well.  Since you're dealing with soft metals, be gentle.. you don't want to change the shape of anything.

New plugs are always nice and often overlooked when you're trying to chase down a "run quality" problem. 

A nice tip I picked up here (from HondaMan I think) for the repetitive task of removal and installation of the airbox is the use of silicon spray.  Use it on the rubber between the air box and the carbs.  Makes one less likely to drink.  hmmmm.

Good luck.  I'm sure you'll get more replies. 

[mixstup]

Thanks Gamma,will again assume the lotus position tonite! I have rebiult a couple of XS650s and these too are cold blooded,I would usually go up 1 or 2 on the mains and 1 up on the pilot to compensate for the pipe and filters.Thanks for your input,Ill get busy with the carb cleaner,cheers,Mick

[Inkscars]

Welcome to the board!
I believe k7 and k8 750s have the same "pd" carbs, if you can verify that, I can probably help!
(or pretend to do so and go home smug. lol)
Do your carbs have the fixed caps on top with the more rectangular shape?
Or are they the thread on round caps?
Like these?

[mixstup]

Hi Inkscar...mine are the PD rectangle tops,cheers,Mick

[Inkscars]

Ok,
I have a 4-1 kerker on my bike with UNI filters, not K&N.
However, our setup is realllly close.
SO, it sounds to me that the slow idle circuit is plugged. That is the brass tube that is pressed into the carb body. Clean carb or not, that's what prevented mine from running off of choke.
SO, a small pair of needle nose or small vice grips and a small piece of cloth (to prevent damage) should pull those little babies out. I cleaned my carbs, NO EXAGGERATION, 4 freaking times before i found a small speck of something in # 2s slow idle jet. try there.
There should be 5 clip positions for your main needle with a little circlip, correct?
Now, my settings are
Main Jet = 120
Main needle position = 2nd from bottom
Air mix screws are out ALMOST 1.5
My slow idle jet size did NOT have to be modified.
When I first got into my carbs, they had 110s in them. I tried every damned combination for several months until i got this right.
I don't know what your climate is there, but our summer ranged between 60 in the am to mid 90s.
Now it has been between 20-55 degrees f and my bike still starts very easily, comes off choke at an appropriate time and runs smoothly at an temperature.
If there is anything else I can help with, please let me know.
I hope this helps.

[mixstup]

Thanks Guys...Ill head out now for some tinkering and report the progress,much appreciated,cheers,Mick

[GammaFlat]

Thanks Guys...Ill head out now for some tinkering and report the progress,much appreciated,cheers,Mick

ahem... Inky's not a guy

77 and 78 carbs are very similar but not identical.  For purposes of this discussion, I think we can call them the same.  If I'm wrong, somebody please correct me. 

John

[mixstup]

"Guys"only meant as a friendly non sexist generic term,no offence intended!! Got busy with the pilot jets,had previously squirted carb cleaner into the orifice but having pulled them out they were filthly!Gave them a good clean,reassembled,turned the air screw back to 1 1/2 turns and rechecked the points and hey presto..runs clean on full choke...have all 4 pots humming...BUT as it warms up and I back the choke off it starts sputtering,makes me think it needs more gas?,plugs don't seem overly white/grey or sooty,getting closer! Cheers comrades,Mick

[GAsohc4]

I have a K8 as well with the pd carbs, I feel for you lol, they're not as easy to deal with or find parts for as the '76 and back
Up side is you/we/I have a more performance oriented carb being that they have accelerator pumps. more like a smoothbore
the accelerator pump really gives them throttle response and off bottom humph but they do have an airflow obstructing flapper
of a choke which is something those mikuni's lack.

my bike runs like crap too I'm running the baffled  "pops hand made" yoshi system and open filters it spits gas outta the overflow tube of either the #1 or #2 carb alternately can"t seem to get it stopped, it smokes alot on start up and a eventually stops almost all together the hotter it gets but won't run with out the choke on unless I'm keeping the revs up
 

[Inkscars]

Glad you found the goo!
Twotired helped me out when I needed it, and those were the little buggers causing my issue.
Now, new issue.
This may sound stupid, but pull off your points cover and get it started.
Loosen the adjuster screws a teeny bit and turn it a TINY smidge (yes that's a measurement) counter clockwise. See if you can take it off choke then.
As far as I know, mine is advanced. Someday, I'll do it the "right" way, but, to hell with it, it runs fantastic NOW. Haha.

Oh, and no offense taken.
Gamma, I do not know if they are exactly identical. I'll see if I can find out. I think 77 and 78 were the same, but, you can never be sure with this many frankenbikes going around.
I find the pd carbs easier to work on myself, but, I've got limited experience with a rack off of a k0 and the 76 has a different set up to.
Maybe someday, when I grow up, I can fix carbs for people and send them a rack that is "bolt on". That would be cool. Lol

[mixstup]

Thanks Inkscars...BIG help,Finally got back to the shop tonite,went through all the obvious stuff again,long story short,checked the timing with the strobe and lo and behold the bugger was way off! Someone hadn't tightened the 3 screws too well in the past .Once I reset the timing and then the points,it now idles off choke.Not great,but at least Im not chasing my tail.Will break out Manometers over the weekend and play some more with the carbs,time now for a pint,Cheers to you ! Mick

[BobbyR]

I have taken my 750K8 carbs apart a few times until I really cleaned them. There is no needle clip adjustment on these carbs. The adjustment screws are true mixture adjustment screws, not air screws.

[Inkscars]

 
You guys know what this means?!?!?!?!?!
My FIRST successful troubleshoot!!!!! 
Not only am I excited that you found your problem, but I'm stoked that I helped someone!
Ok, now I'll be retreating to the south side dive bar again.
Let me know how those carbs come along. I'm happy to help where I can.

[climbingaz]

Great info "GUYS"!

[Inkscars]

Har-dee-har. 

[mixstup]

Hey Comrades,got a chance for a couple of hours of tinker time today...rigged up the tank on a stand with a long piece of fuel hose and rigged up the manometers ,synced them to the #2 Cylinder and Whammo,a sweet idling,responsive,and well mannered motor,ok, so it burps and farts through the filters now and again but what a difference!Still need to play with the settings but Im getting close,if it wasnt for the snow and the fact my wheels are getting rebuilt I wouldve ridden it! Thanks Guys and Inky! for all the help so far.How do you post pics on here?...please go slow as Im hard of learning! Mick

[GammaFlat]

Posting Pictures is covered in FAQs but here's my 2 cents anyway.  

The easy way (my opinion... which is mine ) is to put your photos up on photobucket or use your gmail account to store them (both free options).  

• #1 Assuming you have pictures up on the internet somewhere (if you don't know how to do that, I'll address that below), view the picture online wherever you stored it and right click on it.  You'll get a menu that says something like "copy image location" - select that.  What you're doing is getting a reference or "the address" of that picture on the internet and putting it on the clipboard.  
• #2 Whilst posting a reply, click on the icon third from the left that looks like a picture (just above the smiley emoticon things) - you'll see something like this: "[ img ][ /img]" (with no spaces)
• #3 Your goal is to get the location information you put to the "virtual" clipboard in step #1 between the [ img ] and [ /img].  
• It will end up looking something like this: [ img]http://lh4.ggpht.com/_I1TV61VLMaY/SoTDwGJrnCI/AAAAAAAAGA8/EH18W83wDRs/s800/IMG_0057.JPG[ /img] - again, no spaces in the "real" version - this looks like a big mess but it's much easier than it looks
• #4 Check your work - hit the preview button and see how your picture will look after it's posted
• #5 Hit the post button - voila!

This trick doesn't have to be your own pictures.  With a few limitations, you can grab a picture from anywhere on the net and display it in your post


If you don't have your pictures up on the web, what I'd recommend is to get a GMail account (free email account with Google) where you can store 1 gigabyte of pictures for free (that is a boatload of pictures) - and your pictures never expire.  If you want a GMail account and don't know how to get one, send me a PM and I'll get you an invitation.  Secondly, I'd use Picasa as your photo manager.  It's a painless process to upload your pictures from Picasa to your GMail account.  Picasa is free (I usually don't recommend things that aren't free or cheap ).  Picasa is a very nice picture management program that has tons of other neat features like face recognition, picture tuning, album organization, collages, posters, etc.  

[BobbyR]

works just like he said see

[754]

I think tuning the 77/78 is the same.
 Differences, I know of:
 anodized Aluminum slides vs plated brass

 77 has adjustable needles

 the mounting rack they bolt too, is zinc (gold) plated, on I think 77..and cadmium (silver) on the other

[mick750F]

I think tuning the 77/78 is the same.
 Differences, I know of:
 anodized Aluminum slides vs plated brass

 77 has adjustable needles

 the mounting rack they bolt too, is zinc (gold) plated, on I think 77..and cadmium (silver) on the other

   Always knew about the adjustable needles...'77 had them, '78 didn't. Now I'm going to have to go check out the slides and mounting plates...for no reason other than to know what's what. 

Mike

Mike