Topic: CB500 KO float bowl fuel level.

[Charles T]

Does anybody know from experience or otherwise what the actual fuel level in the float bowl should be on a 1971 CB500 4 KO Keihin carb should or needs to be?
   After very carefully adjusting the floats according to the Honda factory manual (22mm when the needles just close), I found on filling the carbs from the tank, that the actual levels varied from even with the bowl parting line to 3mm below. A variation of 3mm accross the 4 carbs. I ascertained this by using a clear tube on an adapter fitted to the drains of each carb.
    The Clymer manual shows the drain adapter/clear tube trick, but does not give a level. But from the picture it looks to be about 8mm from the top of the float bowl. I know that the higher the fuel level the easier the starting. And that the levels all need to be within 1mm.
But what is that ideal level? If anyone knows i'd be most thankful if they would share it with me.
Regards Charles T

[bryanj]

In 40+ years never checked them that way but your problem would suggest to me that the little pin is not moving properly on one or more of the float needles.

[DaveBarbier]

Generally it’s said that 3-4mm below the bowl seam is good. Not sure if different carbs have different specs, though. Probably not.

[Deltarider]

Frankly said, I find the clear tube method overrated.
1. Floats ra-re-ly need adjustment. I have to see the first one yet.
2. Doing the cleartube method, you must be ab-so-lute-ly sure nothing is hindering fuel flow.
    Incorrect dimensions of the fuellines, incorrect routing (kinking), inline fuel filters, poor venting, all this can be of influence. Think twice before you start adjusting. It's not a regular maintenance thing*.
3. After a long period of inactivity, there's a chance of irregularities like sticking float needles.
4. Cleartube test is best done, when bike is already in daily use. Let the engine run to have some vibes and even then you may have to tinker your testtube or tap the bowl to get a reliable reading.
5. A fuel system cleaner helps the floatvalve and its needle to work smoothly. It kinds of lubes them.
* A manual describes every repair/maintenance that's in theory possible. Only the mecs in the workshops at the dealers that are familiar with your model, can inform you from experience if an incorrect floatlevel is a thing they often see. The answer is: no.

[TwoTired]

In 40+ years never checked them that way but your problem would suggest to me that the little pin is not moving properly on one or more of the float needles.

+1 

I'll add that aftermarket or replacement float needles that don't have that spring pin in the same strength can also alter float heights representing an equal fuel level.

Check the pins for free movement and "push strength".  Make them the same, or make adjustments to bring the fuel level even for all the carbs.

Cheers,

[Charles T]

Thank you all very much for your thoughts and experience, I appreciate it. The reason I adjusted the floats was because I was following the Carb rebuilding procedure outlined in the Honda factory manual. After I cleaned and re-kitted the carbs.( I used Keyster KH-1050N kits, which seem to be a reputable made in Japan brand. And yes they have spring loaded rubber tipped valves.)
     I must be reasonably close. The bike now starts and runs easily. But using a single vac gauge and manometer tube is frustrating me. As the vac levels and idle speed seems to hunt around all over the place when I'm trying to get them all the same. I've got a reputable gauge set on the way. so hopefully seeing all cylinders at once will make it easier. Boy, I didn't realise what a trip this multi cylinder carb business was going to be!

[bryanj]

Single gauge never works as adjusting 1 carb alters the others. Yamaha made one gauge with a rotary switch for balancing there triples and that was next to useless!!