1980 CB 750 carbs...HELP!

[Qball]

@#$&^ piece of *()))(*  You *&@!@#$#$ hunk of #$%%%%
Now thats out of the way.  Anyone had the pleasure of working with the straight four bank of kei hin carbs on an 1980 CB 750?  they are the ones with the vacume slides, not the old mechanical ones (that would be too easy).  OK so here is my problem....They leak fuel.  sounds simple right?  So I have had them apart at minimum 40 times and now I am beyond pissed off.  The bike runs fine but the carbs leak fuel ..alot!

1: Ceck the floats
2:Check the over flow tube for cracks and test floats to make sure they float (solid plastic kind)
3:new float needles (twice cause i didnt trust the first ones)
4:Clean everything! 20 times
5:check the seats
6: nothing wrong with seats so try polishing them up just in case
7:take entire carb bank apart and clean every single bit again
8: test each carb while it is off to find out which carb is leaking because they are all connected you cant tell which one is the culprit.  but none of the carbs leak.
9:put back on bike AGAIN and what do you think happens?  it leaks but this time only for a moment then stops.  Awsome! float needle must have needed to seat itself.  go out to the shop this morning and 10 litres of fuel have pissed all over my shop!

If anyone has a set of these carbs they want to sell/ donate to the angry biker that is loosing his friggin mind in terrace I will be deeply indebted. 

Oh ya I forgot along the way I bought a bank  of carbs off ebay and guess what?  they do the same damn thing! so I took the best parts of both but still no luck.  If no one can help I think I am pushing the bike into my bonfire pit and letting it leak its gas onto the open flame.  One way or another I need to win the war with this bike!

[Fritz]

There are a lot of other people around here with more knowledge than I...hopefully they will throw out something to help

...couple thoughts if it were my bike....are there little plastic connector pipes with seals that feed fuel to and connect each carb ?
Would also be looking at my fuel tap to be sure that it is shutting off...then the leakage would only be from the carbs...now if you know how to True and Balance a Harley flywheel...I will trade you problems
Rusty bucket and the Fast1 have probably worked with these carbs

[fj1200]

Just a guess, but could it be the vent in the gas cap is plugged.  An fj1200 has a singing gas cap, and mine sings all of the time. And it seems to do it at a variety of temps.

[Rusty Bucket]

fast1 must be out of town working;  he has a method for bench testing carbs involving his suspension pump and a fitting jammed into the main fuel supply line,  with the carbs inverted he applies x pressure and says the carbs have to maintain that pressure for x time - the actual figures being unknown to me, but they were high, it was a stiff test.  I have a lower standard test, myself, involving only the tools I came with; with the carbs inverted I apply a vacuum and seal the supply line with my tongue, and expect the level of vacuum to stay the same for 10 seconds -(you'll look like you're playing bagless bagpipes!)  you can wiggle/spin the fuel connectors, and jiggle the individual floats (with the bowls removed), looking for a sudden release of the applied vacuum, hopefully showing the weak link in the chain that keeps the fuel off the floor.   Dave Litke got my extra racks of Honda CB750/900 carbs, but shouldn't there also be a vacuum petcock in that system?  Were the Honda seats the ones that used an O ring seal around the outside of the changable seat , so that even if you had a perfect seat, if the o-rings failed, the fuel could get around the outside of the fitting itself?  That might be a Suzuki/Mikuni thing, rather than Kiehin.  The pressure/vacuum test would show this as well, at any rate.
fast1 and I also have a similar view of the inlet needles and seats that come in many rebuild kits, which seem somehow to mate worse than original sets.  I have had some success re-finishing seats to seal with existing needles by polishing them with an approximation of the needle made out of a dowel, if the needles have stepped you can sometimes move the seal away from the step slightly like this; but it sounds as if you have already done something similar.  No harm in trying this, as you have already,  if replacements are on the way.  One thing about troubles like this - you get really, really good at whipping the racks in and out of the chassis - the first time I took Kevin's carbs out of his CB750F probably took me more than an hour...the 20th probably took 6 minutes.

[Billy Thunder]

I may have a set of these carbs - they need work too, though.

[Qball]

hey billy how much do you want for your carb set?  What kind of floats do they have?  Are they the all plastic or adjustable?  The carbs I have are the 1980 variety with the vaccume slides.  I dont know if you guys have experience with these?  The seats dont seem to be removable?  they are a brass seat though.  I have heard about this problem with the o-ring on the removable seat but have not figured how to get the seat out? I plan on getting out to the shop tomorrow and trying rusty buckets bagpipe meathod.  I think I am down to about 4 min removal and 10 min installation on the carbs.  Man I hope I can figure this out before I go even more crazy. 
Thanks for all the help guys. 

[Billy Thunder]

Q - These carbs need some work, I'll have a quick look. They are not gonna be uber dollars, or maybe we can work out a trade. I'll send you a private message. Let me know if you get it.

[fast1]

  Sorry, don't often scroll down past general. Chances are you have the bastard carbs with the fixed seats. pop the gas cap and release the pressure in the tank. If this solves it venting is your problem. A non vented tank will pressure up and push fuel through the system. Rusty is right, I use a progressive suspension air suspension pump with a gauge. I cut the valve stem off an old inner tube, screw the pump on then stuff the other end into the fuel inlet hose. Turn carbs upside down, bowls off and floats intact. pump up to 5 pounds. should hold pressure for at least 5 minutes. If they leak down spray needle and seat area with wd 40, pump up again and watch for bubbles- just like finding a tire leak. Rusty's blow hard version works too but even if your a non smoker a pound and a half is all ya get.

[The_Heathen]

I did some carb work on my CB650C and had some fuel leaking.  It turned out that the carb wasn't leaking.  Instead the fuel inlet on the carb was a slightly smaller diameter than the outlet on the tank, and fuel was leaking from the between the inlet and the fuel line while the tank outlet/fuel line was totally sealed.  The fuel ran down the carbs, making them look like they were leaking.

[PeggySue]

Hey Qball...
I'm feelin' your pain.
After wrestling the carbs back on this afternoon, getting it all set up and opening up the valve, gas started pouring out... still.
Le sigh. Back to the drawing board.
 
So help me, Honda... it's like you just WANT to sit there, and miss out on the nice weather!

P.

[Qball]

hey peg
Stupid Kehnin carbs!!!!  they piss me off to no end! did we but new float needles in it?  cant remember.  if not I may have some here at the house give me a call and we will try getting you up and going this week.

Q