Keihen CV34 Sync

kz750saskatoon wrote:

I had the petcock set to prime when I was checking the level. Is this not correct? I kind of thought it would have to be set to prime otherwise the fuel level in the carb wouldn't be able to settle to its "final" level.

I did clean out the float valve seats with a Q tip and carb cleaner when I had them apart. I may try rechecking the level by covering the hole and moving the tube like you said you do.

Engine OFF, and with the clear tube in position on dry carb and being held steady against carb, (vac petcock in ON position so no fuel is flowing), THEN turn petcock to PRI so fuel will flow into the float bowl (which also flows into the clear tube).

On CV carb, clear tube is connected to overflow nipple, and drain screw is loosened, all as part of pre-test set-up with dry carb, before lastly allowing fuel to flow into carb.

covering the hole --- :huh: What hole? Don't know of any hole that needs to be covered as part of the clear tube test.

moving the tube --- tube should be held steady and unmoved throughout the clear tube test.

Good Fortune!

I did not realize the carb should be completely dry. That may change things! I learned something today and it is only 835!

"Covering the hole" was referring to JR's post. He said he puts his thumb over the open end of the clear tube if there is an air pocket to lower the tube so that the air goes back into the carb body.

kz750saskatoon wrote:

I did not realize the carb should be completely dry. That may change things! I learned something today and it is only 835!

"Covering the hole" was referring to JR's post. He said he puts his thumb over the open end of the clear tube if there is an air pocket to lower the tube so that the air goes back into the carb body.

"Dry carb" refers to "empty float bowl."

With manual slide carb, filling clear tube with fuel from drain hole, will entail removing the drain screw to attach the clear tube. Removing the drain screw empties the float bowl. So the test starts with an empty float bowl.

Some CV carbs have a dual purpose nipple from bottom of float bowl. Normally, this outlet serves as an overflow when the fuel level gets way too high (one purpose). When the drain screw is partially opened, the same outlet serves as a float bowl drain (other purpose).

Performing the clear tube test on this type of CV carb entails attaching the tube to the nipple, and partially opening the drain screw to allow fuel flow into the tube.
It might work okay to clear tube test a CV carb without first draining the float bowl. Just seems more glitch-free to start with an empty float bowl and allow both the bowl and tube to fill simultaneously (and perhaps help avoid an air bubble in the tube.)

Would defer to JR's experience with CV carb clear tube testing.

Good Fortune!

And next time around I'll try Patton's dry bowl method
but hopefully not until next Spring though .

I do find that if I leave the petcock on Prime the level will - after a time - rise very slowly.

think back to science class. u want to repeat the test the same way each time. if u have the bowl empty and hold the tube in place before turning on the fuel, u will get repeatable results. the bowl doesn't need to be completely empty, but should have to fill during each test. the idea is to have the fuel filling the bowl and the float shutting off the flow, in its usual manner for each test.
if u have the bowl full and lower the tube , the fuel will drain into the tube. then when u raise the tube into posision, the fuel level will be higher, since the float seat will close and trap this EXTRA fuel in the bowl and line. This will distort your test.
i like to put a mark on the tube, so that it is held at the carb at the same length every time. if u were to buy 1 of these tubes, it would have graduated lines right on the tube for measurement purposes. so i have made 1mm graduations on mine as well.this makes things simpler,for me.

I checked the fuel level using the empty-bowl method and still got an air bubble. I tapped the tube a bunch with a screwdriver and the bubble worked itself back into the carb and the fuel came to the specified height (~4mm from the bowl gasket).

Held it there for a while and the level did not rise. Doesn't this indicate that the float needle is closing?

I am going to swap out the bowl. I tested it at the sink with water but maybe there is something else I am missing with that test. Lets me eliminate one more variable.

I had the same problem with my bike...(81 kz750)...I noticed that if I filled the leaking bowl with water, It didn't leak! But! If I filled the bowl with gas it did leak, so I would try that. If it still leaks(with gas, not water) the brass breather tube is leaking somewhere! I took sum gas tank repair putty, and rapped it around the brass tube, mainly on the seam and where the tube connects to the bowl, after 1 hour, I put gas in the bowl again, And to my surprise NO stupid leak anymore...And its been running good since. Hope that will help you if you havn't figured it out.

JR wrote:

And next time around I'll try Patton's dry bowl method
but hopefully not until next Spring though .

I do find that if I leave the petcock on Prime the level will - after a time - rise very slowly.

This generally means you have a suspect needle/seat assembly(s). Some seat assemblies use and o-ring and are pressed into the carb body. Ocassionally the o ring dry rots and allows fuel to weep past the seat. generally no matter what carb config you have, fuel intermittantly leaking out the overflow vent is a bad needle and seat. Tipping the bike side to side and then seeing fuel leak out the overflow can signify too high a float level.

Quick and strange story from years ago, I had a consistant light leak of fuel out the vent on an old RM250 dirtbike. I replaced the needle assmebly TWICE and it kept leaking ! I was going nuts trying to figure out what was going on. Finally upon a very close inspection of the carb bowl brass vent tube I realized the brass tube inself had a thin crack below the fuel level, so the fuel was leaking past the vent tube !

I had another thread in here that dealt with the leak. It turns out, as the last two posters mentioned, the brass overflow tube had a crack. I had looked for it, but did not realize how fine a crack it was. I used JB weld to fill it in and now no leak!