i'd love to ride again - various questions / issues

[DesignBuild]

reporting in: unfortunately no good news.


aside from my carbs being cleaner than i ever thought imaginable, the leak persist.

new o-rings all installed: o-ring > washer > spring > pilot screw.

blew out every nook and cranny with duster, and swabbed everywhere else.

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ok on to acceptance: i set up a rig so i no longer mount to the bike; i put my tank on the bench supported by a couple of 2x4's and racked my carbs inside a stool a foot lower to test.

after initially seeing the leak that rivals BP's blunder in the gulf kept coming, i observed where the gas comes from. first it starts pushing out around the gaskets (which are tight as hell), then moves up to the brass bleed off tube and out the bottom, then if you close that off with your finger it pours out of the engine mount side.

being obvious that for whatever reason my needles still are not seating, i decided to experiment; i took the old o-rings from the pilot screws and put them inside the seat for the needle valve (they happen to be the exact same diameter) to see if that would change anything.... it didn't. this was quite a change in the float height, so i remain skeptical of the floats adjustment being off.

i decided to drain my tank of the remaining gas to check from any rust that might still be breaking through the new filters, i drained it into a clear container.

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theories: my next theory came when i was draining the tank and the container was about full.

please note that my own skepticism and lack of knowledge have already started to debunk this theory:

when the container got to the top and my 3' fuel line was submerged about 6" i thought that due to vacuum the gas should stop flowing once the line is submerged? this was not the case and the gas kept coming. Now that in itself was the theory: shouldn't the vacuum stop the gas flow, and if so and its not, i highly doubt the little needle valves would have enough power to hold back the gas pressure.

now this leads me to believe that maybe my petcock is broke and is not shutting off when the vacuum is lost.

however, if the petcock is purely gravity fed would it not have an internal vacuum shut off and close itself? if so this would mean that this theory is wrong, but if not gas pressure could be why my needle valves are being overwhelmed.

(for reference: my petcock has no vacuum line, and has a "on", "off", and "reserve" setting)

idk, wild theories are all i've got left. if no one wants to take a crack at this, i will ask some of the mechanical engineers who ride at work tomorrow, they generally enjoy a good challenge.

thanks guys.  

[DesignBuild]

i still can't find enough information to go one way or another on the petcock theory, i have read consistently that even if it is bad the needle valve should shut-off the gas flow regardless, so that basically kills the usefulness of that anyways.

i suppose i will break down and buy a float to test to see if it stops the leak, the availability of the 82 floats from anywhere but the most expensive outlets however remains to be slim. From what i've seen, the CB650, CB750K/F, CB900 79-82 all have matching carb parts; does anyone know anywhere that i can get a look at the floats whether they be the plastic non-adjustable or the metal adjustable ones, the only real places i can find are all similar to oldbikebarn.com where they show a diagram and have parts listed but show no real detail. (and are generally overpriced)

if that fails, i've got a guy locally who thinks he knows how to fix it no problem from reading this forum (although i don't know what his "fix" may be). If the labor for the fix exceeds a 100.00 though im just going to part these carbs out and buy a set of CR carbs from a pre 79 model, more availability of parts and mechanical slide to boot! lol

anyone ever swapped the carbs from a 79-82 era DOHC with a pre 79 SOHC bike? are they interchangeable?

[vern401]

Swapping carbs like that I have no idea... The way the floats work is quite simple realy. Being you do not have a fuel pump all fuel is gravity feed. The floats will rise as the fuel level in the bowls rises pushing the needle into the seat. Vacuume has nothing to do with the fuel flow into the bowls on your bike.
Do your floats have ANY liquid in them?
Some times usting a Q-tip and tooth paste you can clean the seat and side walls of the seat.

try this for kicks.
remove the floats and needle from a carb that leaks bad. then with rubber gloves on put your finger over the seat, and turn on the gas. I'm wondering if it is leaking around the seat.
You have new needles and non adjustable floats. If you keep the bowl off and push up on the float does it stop the fuel flow?
Yes = you may need to shim the needle.
No = some other problem.

[DesignBuild]

interesting, i will try that trick of pushing my finger up to close the valve to see where it leaks from.

my only thought on that, although i will still try it, is that i've done that test by pushing the float up with the needle manually and it successfully stopped the gas flow.

i could not see any gas in my floats, and they do all float in a bowl of water. however, since it's getting down to only a few things that could still be an issue, i bit the bullet and ordered a set of four new floats.

they were listed for a 79 but that year had the same design, although it was listed as having two model carbs for that year. The floats looked like a match regardless, they are however adjustable (which i matched the year and seen the adjustments were both 15.5) so i'll now have that functionality.

they arrive friday so i'll see about that.

as for shimming, what exactly does that involve doing? i don't think i could do whatever it is, but i need to know so i can base a labor rate, if the labor goes over 100.00 i would rather cut my losses and swap the carbs with a SOHC model's. The engine design, as far as size and intake port holes and fuel requirements couldn't of been that different between the SOHC and DOHC bikes, atleast thats the hope.

either way for less than a hundred i could buy a new set of my carbs to use the body off of and sell the remaining parts so the labor it might cost could still not be worth it. idk.

[vern401]

Use Q-tips to clean the seats well. an old tooth brush will help in cleaning the carbs off some too.
I use a peace of copper wire from some spare wire I find to "gently" clean out the jet holes etc.
Use the air compressor to blow out all ports and passage ways. You can dunk the carbs beac in the pine-sol and use compredded air to help blow it through them too. Repeated soaking and blowing seems to work best for me. you can make a makeshift ultrasonic system using the soaking container and a sander. the sander vibrates the the container helping to loosen contaminents and pulsate the cleaning solution into the passageways.

[DesignBuild]

Good news time!.. finally.


got my floats in friday, installed and with a few minor adjustments the beast of a leak has subsided.


now i figure i've got a whole slew of new tweaking and things ahead of me, especially since with my airbox on i'm having trouble getting them level which if they are not they want to pour toward the engine intake, but all in all the problem seems to be solved.

now if any of you math wizards out there want to figure out the odds of all four of my floats on my bike going out of adjustment (on non-adjustable floats) at the same time is, i'd like to see that number.

but anywho, thanks for all your help everyone, im insanely relieved that is over.

back to riding!