Topic: Carbies flooding

[Dustproof]

Hi guys,

I have a 1982 CB650SC Nighthawk, it has VB44 carbies and they are giving me grief.  I have put kits through them and replaced the floats and needles, I have an issue where one carby flooding and another that drips.  I have pulled them apart many times and measured things, but they still leak.  Has anyone got experience with the carbs? I probably need parts if anyone has any spare carbies.

Any help would be appreciated

Thanks
Noel

[newday777]

Welcome aboard the forum Noel

Most 'kits' of aftermarket suppliers use inferior brass parts and give the results you are experiencing. Only Keihin brass parts will give you the proper precision quality.
Hopefully you didn't deep six the original brass which can be cleaned and reused.
Float valves you can still order from your Honda dealers.

[Dustproof]

Hi Stu,

I have the original Brass in the carbies at present, all sonically cleaned.  I fitted the floats that are the originals from when I got the bike, they seem to have been slightly modified to stop leaks, so it seems to have been an issue from the get-go.  It's pain to keep pulling the carbs because of leaks, but it seems like something I have to do.  I have a set of carbies from a KZ650 and been toying with swap, but I am resisting putting them on to keep the bike all original.

I believe this bike is the only one in Australia, do you know of any other 1982 CB650SC Nighthawks ?

Thanks
Noel

[scottly]

Hi Noel! I'll move this to the main SOHC board, where it will get more visibility.

[newday777]

Hi Stu,

I have the original Brass in the carbies at present, all sonically cleaned.  I fitted the floats that are the originals from when I got the bike, they seem to have been slightly modified to stop leaks, so it seems to have been an issue from the get-go.  It's pain to keep pulling the carbs because of leaks, but it seems like something I have to do.  I have a set of carbies from a KZ650 and been toying with swap, but I am resisting putting them on to keep the bike all original.

I believe this bike is the only one in Australia, do you know of any other 1982 CB650SC Nighthawks ?

Thanks
Noel

Is there a stylized K on the brass pieces(K is for Keihin)
Are the float valves Keihin or maybe they were put in by the previous owner from an aftermarket 'kit' ??

Have you tested the bowls for leaking overflow tubes? The brass overflow tubes crack when frozen if there was water in the gas in the bowls when left setting over the winter outside in freezing weather.
I test my bowls in the vice(loosely in vice!), fill them with water to the top of the bowl and let set for a half hour to see if any water drips. If one drips, I repair the cracks with soldering to seal the crack.

[newday777]

Here is a cracked overflow tube

And the K to know if the brass is original Keihin brass.  It might be on the face or the side. You might have a polish the brass to see it.

[fizzlebottom]

VB44C carbs do not have overflow tubes in the bowls. Very silly, but that's how they are.

One thing that's pretty common with these carbs is for folks to fiddle with extra sealant around the bowls or pinching a gasket when installing. Definitely take care when installing and make sure the bowl mating surfaces are CLEAN.

If they are actually flooding due to float issues, then you need to closely inspect both the float seat and float needle tip. Additionally, you may benefit from just replacing your floats with new (expensive) ones. They're plastic and that just isn't a forever part. 42/43 years is a lot for a plastic part to deal with.

So, to summarize:

• Check bowl mating surfaces and health of gaskets
• Pay attention to any pinched gaskets
• Inspect float needle tips and seats for any damage
• Consider replacing floats

[Don R]

 Tiny grit can be hiding in fuel lines or petcocks and sneak into the close tolerance of the float needle-seat. I like to remove one float needle at a time and flush the line and carb body by opening the petcock. Also, you mentioned previous modifications to the floats, was the fuel level modified?

[Dustproof]

Sorry for the late reply, life gets in the way sometimes.
I have replaced the floats, but I noticed when the carbies were inverted, the floats had little to no spring from the needle.  To push on the float has no movement as it hits the metal body of the carby. I am wondering if anyone has removed the seat to check for wear.

I have 4 new kits from a reputable supplier (Wemoto) I have run the engine with Liquid Molly 4T carby cleaner to get rid of any crud, it didn't run properly.  I have a bore-o-scope (although a cheap and nasty one) to see if there is damage to the seat.

It might take a little time to respond because the weather is extremely hot here, so the next week or two should cool and I will get to it again.

Thanks for your help
Noel

[Cruiser]

Is the carb vent hole free?

Had similar issues on my bike and one of the vents was just clogged up.

[seanbarney41]

Anytime, any carb or carb racks is violently disturbed you can possibly (actually, more likely than not) see float bowl overflows.  Violently disturbed equals carb removal/installation and parts replacement.  These parts are tiny and fit is sloppy and flexible so float and needle movement can easily jam, bind and otherwise malfunction.  Float bowl tapping can fix it.  Often, a few minutes of engine run time will vibrate things back in to place.  Shaking the bike can fix it.  Best thing I have found is to fill bowl, shut off the gas at the petcock, completely drain bowl via the drain screw, turn the gas on and flush though the drain, turn off fuel, close the drain, refill bowl and repeat this process a few times.  If this does not solve the overflow/leakage you are gonna have to go back in there and find the problem.  Also if your bike has a center stand, use it.  If not, use a wheel chock and/or jack to stand the bike straight up.