Setting carb float hieghts

[DimitriT]

Got this from an excellent Brit mag called "Classic Motorcycle Mechanics".
It occured to me that the reading may be a bit low since the floats and
other parts immersed in the bowl would cause the level to read higher.

 

[49er]

Good idea. It would appear to be a quicker method than running the clear tube from the bowl drain up the side of each carb.
Once all carbs are the same, finito.
Good advice about the fags too. They are hard to re-light after they get soggy.

 

[arveejay]

When you start to lower the bowl to remove it, what happens to the fuel that was above the float valve and hose feeding it? I would think it would run into the bowl the second the float dropped and openend the float valve. Seems like it wouldn't be that accurate if that's the case.

 

[DimitriT]

When you start to lower the bowl to remove it, what happens to the fuel that was above the float valve and hose feeding it? I would think it would run into the bowl the second the float dropped and openend the float valve. Seems like it wouldn't be that accurate if that's the case.

Good point, I guess you need to open up another bowl to drain the extra gas first.

 

[Nightmare]

While i think this might just be nit picking... but i thought you were supposed to measure the float levels with the bike on the centre stand and running as when the carbs are on the bike it is at an angle and things like vibrations will change the overall float height (granted, not by much)...

Its still a pretty good idea

 

[Mike_H]

I like that method. Couldn't you use the tube method while the carbs are in a vice, instead of the very tedious job of removing the bowls from underneath?

 

[t3rmin]

I like that method. Couldn't you use the tube method while the carbs are in a vice, instead of the very tedious job of removing the bowls from underneath?

That'd be the best way to go. No matter what, you're gonna have some gas waiting above the float valve that'll be released when you remove the bowl. Not to mention that it'd be somewhat tedious to remove a full bowl without spilling...

 

[49er]

That'd be the best way to go. No matter what, you're gonna have some gas waiting above the float valve that'll be released when you remove the bowl. Not to mention that it'd be somewhat tedious to remove a full bowl without spilling...

Another method is to ride the bike until it is warm, put it on the main stand and shut off the engine. Do a plug read and identify a plug that shows good colour.
Now carefully drain the contents of that carb bowl into a small glass taking care not to spill any fuel. Mark the level of the fuel on the side of the glass with a vivid pen and use that as your datum for comparison against the other bowl levels. You may find a variance between the carbs. Once you have removed the carbs from the bike,you can adjust the float heights up or down on the other carbs to match.
You can recheck your bowl volumes with the carbs mounted in a vice and level. You need to measure your carbs against the datum again, but the datum carb level needs to be checked also because the carbs could be at a slightly different angle than on the bike.
Once all the levels are identical, mount the carbs, and ride on into sunny skies with flowing, twisty uncongested roads..........................

 

[t3rmin]

Another method is to ride the bike until it is warm, put it on the main stand and shut off the engine. Do a plug read and identify a plug that shows good colour.
Now carefully drain the contents of that carb bowl into a small glass taking care not to spill any fuel. Mark the level of the fuel on the side of the glass with a vivid pen and use that as your datum for comparison against the other bowl levels. You may find a variance between the carbs. Once you have removed the carbs from the bike,you can adjust the float heights up or down on the other carbs to match.
You can recheck your bowl volumes with the carbs mounted in a vice and level. You need to measure your carbs against the datum again, but the datum carb level needs to be checked also because the carbs could be at a slightly different angle than on the bike.
Once all the levels are identical, mount the carbs, and ride on into sunny skies with flowing, twisty uncongested roads..........................

When you drain the reference carb bowl, wouldn't you run into the same issue of the float valve opening as the fuel level drops and letting out additional fuel? Seems like you've got to have the float floating for an accurate read...?

 

[49er]

When you drain the reference carb bowl, wouldn't you run into the same issue of the float valve opening as the fuel level drops and letting out additional fuel? Seems like you've got to have the float floating for an accurate read...?

When the engine is sut down, the petcock valve shuts creating a vacuum which prevents any fuel flowing through the bowl needle jets.
You do however need to ensure that your fuel line is sealed/pinched when bench testing the levels to avoid the problem you mention.

 

[t3rmin]

When the engine is sut down, the petcock valve shuts creating a vacuum which prevents any fuel flowing through the bowl needle jets.

Ahh yes, you're right. ;-) In the interest of thoroughness I'd add that you'd want to make sure you aren't on prime and your petcock is actually shutting off properly.