Topic: carb float height.

[paul_D]

1972 cb500 with 649A carbs

How precise does the carb float height need to be ? Ive measured mine and they vary from 22 to 23mm

[Mo]

I used a set of calipers to set mine, and they're within that range. They're fine, and don't overflow. Just make sure that they don't overflow, but also that they arent too low, or else the bike won't get fuel in the jets and may not send fuel to some cylinders.

[bjbuchanan]

I would say the closer the better obviously. Make sure the individual floats in the carb are at the same level. Overlooked sometimes. a mm or two does make a difference though

[Deltarider]

How precise does the carb float height need to be ? Ive measured mine and they vary from 22 to 23mm

That's OK. Don't worry about a mm more or less. Float heights are ALWAYS right unless people thought it necessary to mess with them before (most of these people are in this forum).
BTW, interesting to see somebody in Canada has 649A carbs. Did your 500 come from Europe?

[lucky]

How precise does the carb float height need to be ? Ive measured mine and they vary from 22 to 23mm

That's OK. Don't worry about a mm more or less. Float heights are ALWAYS right unless people thought it necessary to mess with them before (most of these people are in this forum).
BTW, interesting to see somebody in Canada has 649A carbs. Did your 500 come from Europe?

I agree completely.
IF it has not had new float needles in two years of riding, get new ones but do not try to adjust the floats to get them to stop leaking.

[Duanob]

Your best bet is to get a clear tube float level tool. It screws into the drain screw and will give you the level while the carbs are on the bike. Should be a mm or 2 below the lip of the carb bowl.

[bjbuchanan]

I can't understand the persistence to use the clear tube method. I don't get what is so killer about getting the rack off of there and making sure it is spot on to where you want with no guesstimation. You can check out the rest of the rack at the same time too. I have a 750 with stock airbox so I know it is not exactly fun either

[paul_D]

How precise does the carb float height need to be ? Ive measured mine and they vary from 22 to 23mm

That's OK. Don't worry about a mm more or less. Float heights are ALWAYS right unless people thought it necessary to mess with them before (most of these people are in this forum).
BTW, interesting to see somebody in Canada has 649A carbs. Did your 500 come from Europe?

Yes the bike is from europe, I dont recall where. The bike is a mismash.

cb500-2057419    stamped 1974
cb500E-2145923

and 649A carbs with 125 main jets (PO) and no hump ram intake under the seat.

[Duanob]

I can't understand the persistence to use the clear tube method. I don't get what is so killer about getting the rack off of there and making sure it is spot on to where you want with no guesstimation. You can check out the rest of the rack at the same time too. I have a 750 with stock airbox so I know it is not exactly fun either

Sorry to be in such a fiesty mood today but if you can't understand it then i am not going to explain it.

[flybox1]

I can't understand the persistence to use the clear tube method. I don't get what is so killer about getting the rack off of there and making sure it is spot on to where you want with no guesstimation. You can check out the rest of the rack at the same time too. I have a 750 with stock airbox so I know it is not exactly fun either

Sorry to be in such a fiesty mood today but if you can't understand it then i am not going to explain it.

..easy there D! 

..because a change of 1mm in float height equates to more than 1mm change in bowl fuel level.
both my 350 and my 750 run best when the bowl fuel levels are correct (@3-4mm below bowl gasket seam). 
sometime this level is achieved the shop manual float height suggested setting, sometime is not.
ie. 350F shop and clymer sugg 21mm.  23-24mm gets you the correct bowl fuel level height fi you have stock 350F floats.

none of this can be completed/dialed in without a clear tube.

[bjbuchanan]

Bluntness comes across too harsh through typing it wasn't intended to be too rough. I understand the principle and the usefulness but I still believe that getting the rack off there and being sure of the actual measurement is best.

I don't like to recommend the clear tube because it seems like guys that aren't sure what they are doing try to half @ss it and then can't figure out why it didn't work. I'm not saying the thread poster can't get it but still, IDK

[lucky]

I can't understand the persistence to use the clear tube method. I don't get what is so killer about getting the rack off of there and making sure it is spot on to where you want with no guesstimation. You can check out the rest of the rack at the same time too. I have a 750 with stock airbox so I know it is not exactly fun either

I do not understand that either.
Even the shop manual says to measure the floats BEFORE.... using that clear tube method.

[scottly]

I can't understand the persistence to use the clear tube method. I don't get what is so killer about getting the rack off of there and making sure it is spot on to where you want with no guesstimation. You can check out the rest of the rack at the same time too. I have a 750 with stock airbox so I know it is not exactly fun either

I do not understand that either.
Even the shop manual says to measure the floats BEFORE.... using that clear tube method.

I don't understand the reluctance to accept the clear tube as the ONLY accurate measure of the level in the float bowl. The bench measurements are a good starting point, but the clear tube tells you what is really happening.

[flybox1]

Remember what the goal is.  PROPER FUEL LEVEL. 
Can you see fuel level through your bowl?

[lucky]

Remember what the goal is.  PROPER FUEL LEVEL. 
Can you see fuel level through your bowl?

The proper fuel level is achieved by taking a measurement of the float as shown in the shop manual.

 Photo at the bottom of Page #125. Chapter 6

[Joemac]

Your best bet is to get a clear tube float level tool. It screws into the drain screw and will give you the level while the carbs are on the bike. Should be a mm or 2 below the lip of the carb bowl.

Can you recommend where i can get one of these?

[disco]

+1 to what Scottly & Flybox said....the aim is to get the proper fuel level across all 4 bowls. Start by using the measurements to get it in the ballpark & then check it using the clear tube. Make adjustments as necessary.

[HondanutRider]

Your best bet is to get a clear tube float level tool. It screws into the drain screw and will give you the level while the carbs are on the bike. Should be a mm or 2 below the lip of the carb bowl.

Can you recommend where i can get one of these?

It's been described before, elsewhere in this forum: 

Take a section of clear aquarium hose and in a middle section gently heat it up (e.g. with a match held below).  Rotate and pull the tube so-as to stretch and shrink the heated portion.  Cut the shrunken section in the middle to create two pieces of hose that can be stuffed/screwed into the float bowl's drain hole to make a "reasonable" seal that will hold fuel while you do the test on a non-running machine.  By making four sections of hose this way, and looping the ends upwards while you turn on the petcock to fill the bowls, you can see the level of the fuel in the bowl by how high it goes in the tubes.  The seal is temporary and precarious, so you wouldn't want to leave the tubes installed while running or operating the motorcycle.

[Eddie]

Also, wouldnt the float height change if the front or rear of the bike is higher or lower ? (saggy springs, different tire sizes, modifications) . So I can see the clear tube is the best method.

[Duanob]

Remember what the goal is.  PROPER FUEL LEVEL. 
Can you see fuel level through your bowl?

The proper fuel level is achieved by taking a measurement of the float as shown in the shop manual.

 Photo at the bottom of Page #125. Chapter 6

Yes it is but floats can get stuck when installing the float bowl or the leaf spring can get twisted a bit and block the flaot from working properly, all kinds of s#&%#(*! can happen from the time you set your floats and start the bike up.


Joemac I got mine on ebay I see them all the time for cheap.

[lucky]

I can't understand the persistence to use the clear tube method. I don't get what is so killer about getting the rack off of there and making sure it is spot on to where you want with no guesstimation. You can check out the rest of the rack at the same time too. I have a 750 with stock airbox so I know it is not exactly fun either

I have said this over and over.
The Clymers workshop manual specifically says to measure the float height and they show a photo.
It also says, To MEASURE the float height BEFORE using the clear tube method.

I worked in a dealership and we always just measured them like the book shows.
We never used the clear tube method and we never had any problems.
But you must have new float needles.

You cannot use old worn out float needles and get good results.

The float operation and float needle is 90% of making the carb work right!