Author Topic: Testing carb float levels with water?  (Read 329 times)

Offline paulbaker1954

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Testing carb float levels with water?
« on: May 14, 2018, 04:56:18 PM »
May sound a daft question but am just rebuilding my carbs and wondered if i can test the float level using water (off bike of course !!!)

Just hate messing around with petrol all over the place

But maybe water has some different physical property from petrol that means its not feasible

Also does the level need to be about 2mm below the bowl/body joint from memory?
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Offline hairygit

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Re: Testing carb float levels with water?
« Reply #1 on: May 14, 2018, 05:01:42 PM »
Personally I wouldn't use water, maybe paraffin or meths or even diesel would be better.
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Offline kevski

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Re: Testing carb float levels with water?
« Reply #2 on: May 14, 2018, 06:51:31 PM »
Better off using petrol as anything else has a different densities and the floats will be at different levels, just be sensible and you will be fine.

Offline paulbaker1954

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Re: Testing carb float levels with water?
« Reply #3 on: May 14, 2018, 07:07:11 PM »
Better off using petrol as anything else has a different densities and the floats will be at different levels, just be sensible and you will be fine.

That’s what I thought given my aged memory of physics and eureka
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Offline deltarider

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Re: Testing carb float levels with water?
« Reply #4 on: May 14, 2018, 07:58:51 PM »
Rule of thumb: the floatlevels are NEVER wrong unless floats have been messed with. I sure hope this American epidemic doesn't spread here.

Offline Rob62

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Re: Testing carb float levels with water?
« Reply #5 on: May 14, 2018, 09:16:50 PM »
Cant you just use a guage or a rule like it says in the manual?

Offline kevski

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Re: Testing carb float levels with water?
« Reply #6 on: May 14, 2018, 10:13:29 PM »
Rule of thumb: the floatlevels are NEVER wrong unless floats have been messed with. I sure hope this American epidemic doesn't spread here.
As bike is 40+ years old, Rule of thumb is check the float levels, as you never know what previous idiots, err i mean owners have done.

Offline deltarider

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Re: Testing carb float levels with water?
« Reply #7 on: May 15, 2018, 07:09:16 AM »
Rule of thumb: the floatlevels are NEVER wrong unless floats have been messed with. I sure hope this American epidemic doesn't spread here.
As bike is 40+ years old, Rule of thumb is check the float levels, as you never know what previous idiots, err i mean owners have done.
Unfortunately too many mistake another problem for an incorrect floatheight. Incorrect fuelline length and diameter (kinking), good-for-nothing 'extra' inline fuelfilters that intermittently hinder fuelflow and sticking valveneedles. It takes very little indeed, to disturb the gravity feed of just a few centimeters difference in height. I would start with having the correct fuellines and - especially after hibernation - eliminating sticking valve needles. An additive may help. I myself have never encountered a CB500/550 float that needed to have it's tang adjusted.
The correct dimensions for CB500 fuellines is 18 and 30 cm (old style petcock) or 17 and 28 cm for models that had the newer type petcock. ⌀ 5,5 mm.

Offline kevski

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Re: Testing carb float levels with water?
« Reply #8 on: May 15, 2018, 07:15:02 AM »
Rule of thumb: the floatlevels are NEVER wrong unless floats have been messed with. I sure hope this American epidemic doesn't spread here.
As bike is 40+ years old, Rule of thumb is check the float levels, as you never know what previous idiots, err i mean owners have done.
Unfortunately too many mistake another problem for an incorrect floatheight. Incorrect fuelline length and diameter (kinking), good-for-nothing 'extra' inline fuelfilters that intermittently hinder fuelflow and sticking valveneedles. It takes very little indeed, to disturb the gravity feed of just a few centimeters difference in height. I would start with having the correct fuellines and - especially after hibernation - eliminating sticking valve needles. An additive may help. I myself have never encountered a CB500/550 float that needed to have it's tang adjusted.
The correct dimensions for CB500 fuellines is 18 and 30 cm (old style petcock) or 17 and 28 cm for models that had the newer type petcock. ⌀ 5,5 mm.
You are missing the point, Check does not mean adjust and previous owners, to blythly refurb which original poster is doing without checking everything would be foolhardy.
« Last Edit: May 15, 2018, 07:16:41 AM by kevski »

Offline paulbaker1954

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Re: Testing carb float levels with water?
« Reply #9 on: May 15, 2018, 12:56:19 PM »
Rule of thumb: the floatlevels are NEVER wrong unless floats have been messed with. I sure hope this American epidemic doesn't spread here.
As bike is 40+ years old, Rule of thumb is check the float levels, as you never know what previous idiots, err i mean owners have done.
Unfortunately too many mistake another problem for an incorrect floatheight. Incorrect fuelline length and diameter (kinking), good-for-nothing 'extra' inline fuelfilters that intermittently hinder fuelflow and sticking valveneedles. It takes very little indeed, to disturb the gravity feed of just a few centimeters difference in height. I would start with having the correct fuellines and - especially after hibernation - eliminating sticking valve needles. An additive may help. I myself have never encountered a CB500/550 float that needed to have it's tang adjusted.
The correct dimensions for CB500 fuellines is 18 and 30 cm (old style petcock) or 17 and 28 cm for models that had the newer type petcock. ⌀ 5,5 mm.
You are missing the point, Check does not mean adjust and previous owners, to blythly refurb which original poster is doing without checking everything would be foolhardy.

Concur whats the point of stripping the carbs, ultrasonic clean, new jets and O rings and NOT checking float levels !!!!

BAck to my original question should the level be about 2 mm below the bowl/body join line. I am sure I have seen a number of posts on this but cant seem to locate obe
If you think there's light at the end of the tunnel it's usually another train !!

2016 Yamaha MT09 Tracer
1971 Honda CB500 Four K0

Offline Seabeowner

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Re: Testing carb float levels with water?
« Reply #10 on: May 15, 2018, 03:09:35 PM »
The manual only shows a measurement with the bowl removed, with the carbs on their side with the float tang just touching the needle. It should be 22mm from the flange to (what is) the bottom of the float.
But 2mm below the flange for the (so called) clear tube test is what I use.
The tang is pretty stiff and will not change unless interfered with, but aftermarket needles may alter level.
Phil
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1973  CB500K1
1975  CB550F1
1978  CB550K

Offline kevski

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Re: Testing carb float levels with water?
« Reply #11 on: May 15, 2018, 03:53:27 PM »
The manual only shows a measurement with the bowl removed, with the carbs on their side with the float tang just touching the needle. It should be 22mm from the flange to (what is) the bottom of the float.
But 2mm below the flange for the (so called) clear tube test is what I use.
The tang is pretty stiff and will not change unless interfered with, but aftermarket needles may alter level.

Agree with this, i have after market needles in my 350/4, i had to adjust the tangs on the floats as the needles were shorter and would not shut off the fuel supply.

Offline taysidedragon

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Re: Testing carb float levels with water?
« Reply #12 on: May 15, 2018, 05:04:51 PM »
May sound a daft question but am just rebuilding my carbs and wondered if i can test the float level using water (off bike of course !!!)

Just hate messing around with petrol all over the place

But maybe water has some different physical property from petrol that means its not feasible

Also does the level need to be about 2mm below the bowl/body joint from memory?

I found that testing with water doesn't work!

I had a fuel drip from the float bowl overflow pipe on my 400/4. It had new float valves but I checked the one that was dripping for dirt and made sure it was seating ok. Still dripping.  :(

I'd read that the brass overflow pipes sometimes crack and cause a leak so I took off the float bowl again and filled it with water. No leaks, so it must be ok, right? Wrong.

When I checked the bowl again with fuel it didn't leak at first, but after a minute or so it started dripping very slowly and the outside surface of the external pipe was wet. It must be finding a way down the side of the pipe between the aluminium bowl and the pipe.

I won't check with water again.  >:(
2010 Street TripleR
1977 CB400F

Offline matthewmosse

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Re: Testing carb float levels with water?
« Reply #13 on: May 15, 2018, 05:52:37 PM »
Water might well not find it's way through a gap petrol will creep through. I wouldn't  be using it as it's asking for a tiny bit to stay behind and cause alloy to corrode and block something or dry out and leave a deposit of stuff to block jets. Carbs are a pain to start with so deffinately worth checking so as to avoid future doubt and stripping and reassembly. But I would do all checks with fuel, it may smell bad etc but it's what you are trying to get it working with so you eliminate variables and Don't introduce things that are not meant to be there and bring their own issues.
Got a 500/4 with rust and a sidecar and loadsa bits. nice and original and been round the clock

Offline paulbaker1954

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Re: Testing carb float levels with water?
« Reply #14 on: May 16, 2018, 06:45:11 AM »
May sound a daft question but am just rebuilding my carbs and wondered if i can test the float level using water (off bike of course !!!)

Just hate messing around with petrol all over the place

But maybe water has some different physical property from petrol that means its not feasible

Also does the level need to be about 2mm below the bowl/body joint from memory?

I found that testing with water doesn't work!

I had a fuel drip from the float bowl overflow pipe on my 400/4. It had new float valves but I checked the one that was dripping for dirt and made sure it was seating ok. Still dripping.  :(

I'd read that the brass overflow pipes sometimes crack and cause a leak so I took off the float bowl again and filled it with water. No leaks, so it must be ok, right? Wrong.


Well known issue is hairline cracks in the overflow pipe. I once spent ages trying to chase down what I thought was a float valve not seating only to eventually spot this hairline crack

I tried fixing it with jd weld but eventually petrol ate its way past it and gave up and sourced a new float bowl but they are getting harder to find at sensible prices

When I checked the bowl again with fuel it didn't leak at first, but after a minute or so it started dripping very slowly and the outside surface of the external pipe was wet. It must be finding a way down the side of the pipe between the aluminium bowl and the pipe.

I won't check with water again.  >:(
If you think there's light at the end of the tunnel it's usually another train !!

2016 Yamaha MT09 Tracer
1971 Honda CB500 Four K0