Topic: Clear tube method of checking float height

[bytio]

Hi all,
I am aware of this method in putting clear tubing on the bowl drains and opening the drain screw which will fill the tube to the level of fuel in the carb.
My question is how do you know which level is correct, example my 78F carbs have a req float height of 14.5 mm where would I expect to see the fuel level in the tubes for this.
Thanks for any info

[flybox1]

if your floats are set accurately....3-4 mm below the bowl gasket mating surface.

[crazypj]

Honda don't give a spec for fuel level, back 'in the day' Kawasaki were the only manufacturer who did. It's a PITA when it's all you have  - they didn't give a basic float height

[seanbarney41]

the clear tube method is helpful when correct and accurate adjustment of the float height doesn't necessarily result in the correct fuel level in the bowl

[PeWe]

The fuel level in the bowls is the goal however it will be done. Why measure when the actual visible fuel level is the real thing??

[seanbarney41]

The fuel level in the bowls is the goal however it will be done. Why measure when the actual visible fuel level is the real thing??

agreed

[dave500]

having them set dead even and perfect isn't critical,picture whats happening inside the bowls when your riding,its like a washing machine inside,dont sweat it too much.

[Don R]

the clear tube method is helpful when correct and accurate adjustment of the float height doesn't necessarily result in the correct fuel level in the bowl

Agreed.

[Deltarider]

having them set dead even and perfect isn't critical,picture whats happening inside the bowls when your riding,its like a washing machine inside,dont sweat it too much.

Thanks Dave. I've made a point of this since long but the floatadjusting epidemic seems to continue. I repeat: I've never seen the floatheight change from factory spec unless people with restless hands start messing with it. Not everything described in manuals is necessary.

[TwoTired]

The fuel level in the bowls is the goal however it will be done. Why measure when the actual visible fuel level is the real thing??

Because, if the fuel level is wrong even when the mechanical measurement is correct, there is good reason to believe that alteration or defects of the associated determining components is suspect.

The fuel level average level (whether it bounces around or not) effects the distance and pressure differential required to raise the fuel into the carb throat.  This will effect average mixtures delivered, as the airflow volume through the carb isn't effected by the same factors.

[crazypj]

the clear tube method is helpful when correct and accurate adjustment of the float height doesn't necessarily result in the correct fuel level in the bowl

 And what are you going to set it at?
 guess an arbitrary fuel level?

[seanbarney41]

the clear tube method is helpful when correct and accurate adjustment of the float height doesn't necessarily result in the correct fuel level in the bowl

 And what are you going to set it at?
 guess an arbitrary fuel level?

that's a good question.   it seems like somebody, somewhere around here figured out that 3-4mm below the float bowl gasket works good.  That's the figure I have aimed for on a wide variety of 1970's Hondas and it seems to work

[flybox1]

Set floats correctly...and measure the fuel level.  That's what you'll get.
Years ago I had an issue with my 350f, clymer specs for float height were wrong, and Hondaman and I sorted it out.  The 3-4mm below gasket seam level is a number he mentioned as a fuel level needed to cover the main and pilot jet, but not the overflow tubes in all circumstances....

[crazypj]

6~7mm from gasket face would also cover the pilot and main jet, don't think it would run very well though (haven't tried so don't know for sure)
The float level +/- isn't a tolerance but a method to adjust fuel delivery to correct or compensate for a running issue, higher lean's out everything slightly, lower richens everything slightly, it's a coarse way to adjust for elevation without changing jets.
You can correctly set float level and check fuel level but you need a number not a range then check all the carbs are the same in a bank
With production tolerances 3~4mm fuel level is OK to get running but not accurate enough for good running

[seanbarney41]

6~7mm from gasket face would also cover the pilot and main jet, don't think it would run very well though (haven't tried so don't know for sure)
The float level +/- isn't a tolerance but a method to adjust fuel delivery to correct or compensate for a running issue, higher lean's out everything slightly, lower richens everything slightly, it's a coarse way to adjust for elevation without changing jets.
You can correctly set float level and check fuel level but you need a number not a range then check all the carbs are the same in a bank
With production tolerances 3~4mm fuel level is OK to get running but not accurate enough for good running

interesting...I remember that certain Clymer manuals seem to suggest using float height/fuel level as a tuning parameter rather than just sticking with the factory specified float height, but have not really ever given it a very scientific try.  Would raising the fuel level tend to richen the mixture throughout the whole range of throttle positions?

[AJK]

6~7mm from gasket face would also cover the pilot and main jet, don't think it would run very well though (haven't tried so don't know for sure)
The float level +/- isn't a tolerance but a method to adjust fuel delivery to correct or compensate for a running issue, higher lean's out everything slightly, lower richens everything slightly, it's a coarse way to adjust for elevation without changing jets.
You can correctly set float level and check fuel level but you need a number not a range then check all the carbs are the same in a bank
With production tolerances 3~4mm fuel level is OK to get running but not accurate enough for good running

interesting...I remember that certain Clymer manuals seem to suggest using float height/fuel level as a tuning parameter rather than just sticking with the factory specified float height, but have not really ever given it a very scientific try.  Would raising the fuel level tend to richen the mixture throughout the whole range of throttle positions?

Yes. All carb circuits depend on float level. Raise it and all circuits see a richer mixture. This is just physics.

[TwoTired]

the clear tube method is helpful when correct and accurate adjustment of the float height doesn't necessarily result in the correct fuel level in the bowl

 And what are you going to set it at?
 guess an arbitrary fuel level?

Based on checks of several 550 carb sets and a few 750 PD carbs, 2-3mm below gasket surface is what they measure using the proper mechanical float setting.  They run pretty well this way.  This is while using stock components, exhaust, induction, and original Keihin carb components.  No aftermarket anything, besides a UNI NU 4055 air filter.

Works for me...

[andrewk]

having them set dead even and perfect isn't critical,picture whats happening inside the bowls when your riding,its like a washing machine inside,dont sweat it too much.

Thanks Dave. I've made a point of this since long but the floatadjusting epidemic seems to continue. I repeat: I've never seen the floatheight change from factory spec unless people with restless hands start messing with it. Not everything described in manuals is necessary.

How many sohc4's do you encounter that haven't been messed with endlessly at some point in the last 40 years?  People interested in getting their bikes running correctly will check and adjust the float height as necessary (like when installing new needles) if for no other reason than undoing 40 years worth of other people's idle hands messing with things.  Carb sync is the same thing.  Might have been perfect new, but where has it been, and who has messed with it before you?

I'm all in agreement that Honda set the floats correctly when new.  But I challenge you to find a used bike that hasn't had some ham-fisted jerk dicking with the carbs (and everything else) at some point in its life.  Those of you on the forum lucky enough to be original/2nd owners, the rest of us are jealous.  

[lucky]

Hi all,
I am aware of this method in putting clear tubing on the bowl drains and opening the drain screw which will fill the tube to the level of fuel in the carb.
My question is how do you know which level is correct, example my 78F carbs have a req float height of 14.5 mm where would I expect to see the fuel level in the tubes for this.
Thanks for any info

Yes you can think for yourself!!

Where is any Honda literature saying how the 14.5mm will be translated into mm above some part of the carb. And if the gas was at this level wouldn't it be above the float bowl overflow tube?

Just a few months ago the same people were saying 2-3 mm above the float bowl edge.
Where did this come from?

[Deltarider]

How many sohc4's do you encounter that haven't been messed with endlessly at some point in the last 40 years?

I can assure you there is a big difference between SOHC's in Europe and US as far as miles on the odometer and I can assure you that on European fora where people own Honda's with far more miles on the clock than in the US float adjusting is rarely discussed if ever. That leads me to the conclusion that by echoing this float adjusting thing over and over it becomes a bias to new readers of this forum. My sympathy is with them.

People interested in getting their bikes running correctly will check and adjust the float height as necessary (like when installing new needles) if for no other reason than undoing 40 years worth of other people's idle hands messing with things.

Nothing wrong with checking but think twice before you judge it necessary to adjust. How likely is it that PO's that only did 20.000 miles or so went on their knees to perform such a difficult task as removing 4 floatbowls and then start bending tiny little tangs in the most complicated and delicate parts of their bike?

[andrewk]

How many sohc4's do you encounter that haven't been messed with endlessly at some point in the last 40 years?

I can assure you there is a big difference between SOHC's in Europe and US as far as miles on the odometer and I can assure you that on European fora where people own Honda's with far more miles on the clock than in the US float adjusting is rarely discussed if ever. That leads me to the conclusion that by echoing this float adjusting thing over and over it becomes a bias to new readers of this forum. My sympathy is with them.

Mileage is what keeps these things alive. Nearly everyone here is resurrecting a used bike that has been messed with before. Some are worse than others.  I would also say that float adjusting is so flipping simple and clear in the manual that you EU guys probably don't need to talk about it.  Beginners don't buy expensive (relative to USA) old Japanese bikes in Europe much, do they?

How likely is it that PO's that only did 20.000 miles or so went on their knees to perform such a difficult task as removing 4 floatbowls and then start bending tiny little tangs in the most complicated and delicate parts of their bike?

Around here it's pretty likely. Nearly every old bike in this part of the US has sat with fuel in it for an extended period of time at some point in its life.  Higher mileage bikes are likely to have junky aftermarket parts in them (another reason to necessitate float level change is making cheap parts work right) and the low mile bikes have probably been "resurrected" twice before any of us see them.  These bikes had/have a "cheap" reputation as well, which leads a lot more amateurs to work on them without being "afraid to mess up something expensive," which is a real tragedy.

I don't understand the hesitation to adjust something when you find it out of spec.  Certainly leave it alone if it's good but why put something back together that's incorrect?  Seems like a good way to chase your tail.

[PeWe]

I measured my floats, not very exact when I did not change them back in the days.
Looked more for all had same meaurement, close to spec. Engine ran very rich and I verified the advices I got on this forum to be true, float level was too high.
Float height in mm is the initial setting that hopefully end up correctly when verify it by practical test as Clear tube, the only way to verify it as I know.
Clear tube will also show if a float is stucked (bent hitting the carb), leaking float valves.

[AJK]

TT is 100%. Bikes, motors, carbs, etc are dead stupid, just like computers. All they do is follow the laws of physics & nothing more. If something is out of spec, then leaving it uncorrected will just lead to non-optimal performance. Even an un-touched bike will have its needle and seat worn to some degree after miles are put on it, resulting in a different float level than what was first on it.
  In my view, the float level is the dependency by which all fuel delivery circuits in the carbs are based on. Its something that i do first before even considering any other tunable aspect of a carb like pilot or main jet sizes, because once you change the float level, it throws out all other settings as well.
  TT is also 100% that its the average float level that matters in the carb. The fuel is choppy in there, but there will be an average level that the main jet 'sees', and its this average level that is either easier (or harder) to push into the engine depending on how high (or low) it is.

[Don R]

I learned a PO may have done anything to a carb. Mine had the jets drilled, the floats were way off too. I got it unfinished from a former Honda tech but I'm sure the previous owned did the damage. I rode it to where he works once after I got it right, he was astonished it ran so well. Or auctually, even ran.
 I experimented with float level, it makes a big difference in fuel air ratios.

[DH]

Adjusting Carburetor Float Level


I found this interesting.