Float height adjustment

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kettle738
Posts: 225
Joined: Wed May 26, 2010 10:24 am
Location: Romney Marsh, Kent.

Float height adjustment

Post by kettle738 »

Hi all, adjusting the float heights should be a very simple task, but it's confused by conflicting information as to where the measurement is made from.

For the GT750J the original Suzuki manual quotes a float height of 27mm and the diagram clearly shows the measurement being made from the flanged edge of the carb body.

For the same carbs Gunnar Forsgrens site (which I would implicitly trust as he seems to get pretty much everything right) here............

http://suzuki.medial.com/carbs/index.html

shows the measurement being made from the gasket face with the gasket removed, and that is a considerable difference.

For the later models, Haynes uses the revised measurement (25.8mm) but refers to the same diagram as the Suzuki manual, measuring from the carb flange.

Baz's excellent DVD is quite specific and takes the measurement from the gasket surface.

Does anyone know which is correct and why......for both the J/K and the later models?

Mick...............................kettle738
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BAZ
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Re: Float height adjustment

Post by BAZ »

My way of measuring is for CV Carbs only and was cross checked by measuring amount of fuel in the chamber. I will be restoring some slide carbs soon and I will update you.
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yeadon_m
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Joined: Sat Jan 02, 2010 7:10 am
Location: Canterbury Kent

Re: Float height adjustment

Post by yeadon_m »

Mick,

Measure float height to bare surface gasket sits on, with gasklet removed. If you are using stock float needle valves, tilt the carbs until tangs on floats are 'just touching' the tips of the needles, but not compressing them.
If you are using aftermarket eg Keyster needle valves, as they have stronger springs, invert the carb letting float weight rest on needle and make same measurement per manual.

It is easy to get fuel height wrong and be over rich or lean. Each will produce characteristic symptoms when riding.

What if any symptoms do you have when riding that prompts you to adjust float height?

Cheers!
Mike
kettle738
Posts: 225
Joined: Wed May 26, 2010 10:24 am
Location: Romney Marsh, Kent.

Re: Float height adjustment

Post by kettle738 »

Thank you for the input which is much appreciated. Ian Sandy (Author of Old Japanese Bikes / GT750 Field Guide ) very kindly sent me a link to a Suzuki technical bulletin from 1975 which directly addresses the issue. In short it states the float height measurement should be taken from the 'float bowl fitting surface' which could otherwise be described as the bare gasket surface. This contradicts Suzuki's own workshop manual, which describes in text and diagrams taking the measurement from the carburettor flange, and is the reason I asked the question.

http://www.ozebook.com/compendium/techb ... %206-9.pdf

I thought I had scoured all the Ozebook tech bulletins, but I'd missed this one and it's one of the most useful with a whole pile of data for the two stroke range, also it post dates the Suzuki manual, so I am happy to take this as the last word on where the float measurement should be taken from. It makes no difference if you use a fuel level gauge as that is another method of achieving the same result, and of course you could still measure from the flange or gasket surface by measuring and deducting the difference from the basic measurement, but it is hugely useful, to me at least to have a standard reference to work from. This forum works!

Mick..............kettle738
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Bikesklade
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Joined: Sat May 15, 2021 9:16 am

Re: Float height adjustment

Post by Bikesklade »

Hi I have just gone to set the float heights on my 750L CV carbs

The manual says 27.6mm, set them to that, measured from the inside flange face not gasket .....Put them back together, connected them to a dummy fuel tank "no vacuum tap fitted" on the bench to leak test and no fuel getting to any of the float bowls. Blew through the fuel line and all blocked/sealed. Removed the float bowls blew through and all good.

The floats seam very high and I hand to bend the tag along way to achieve the required measurement. I have since noticed some details about after market fuel valves have a different setting 25mm, I also see that the Haynes manual say that the valves are sprung loaded.. mine are not, and no I have not lost the springs, are they the aftermarket items?

Any ideas please

Regards
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Bikesklade
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Re: Float height adjustment

Post by Bikesklade »

Panic over all sorted now

Regards
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Bikesklade
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Joined: Sat May 15, 2021 9:16 am

Re: Float height adjustment

Post by Bikesklade »

I am sure this has been discussed a 100 times. But here is my experience.

Set the float heights at 27.6mm measured from the gasket fitting surface to the top of the floats. "I have Brooks Barn Needle jets fitted" as per SUZUKI Service Bulletin dated 11/07/1975 and the bike starts with the slightest of flicks on the kick starter or button either cold or Hot. Ticks over at 1100 RPM and revs to the red line with ease. Plugs are a nice brown colour after a 100 mile brisk ride

Sweet

And I also wanted to mention, my experience with my starter clutch .... When I got the bike is ran, but really not properly, I changed all the usual things, Cleaned the carbs, new points condensers and plugs .. Still not right, so I invested in a DTI so I could set up the ignition timing. Upon checking I found the following. Instead of the left hand cylinder points being about to open at 3.64mm BTDC I found the right hand set was about to open, clearly not right. So I removed the points assembly and starter clutch and found the keyway had completely sheared off and the unit was around 180 degrees out, how the bike ran at all I don't know, but I can assure you it did. So I bought a new keyway lapped the damage out of the shaft refitted it and set the timing up as described ion the manual. Switched on, and hey presto starts and runs as I know it should. Beautiful to ride.

Hope that helps anyone that may have a similar problem.
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PaulD738
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Re: Float height adjustment

Post by PaulD738 »

The float height is just a guide so you can get the FUEL level in the carb bowl correct. I made these up for my Katana but I’ve also got some made up for my T500 and Kettle. You remove the drain plug and screw the adapter in. When the carb bowl fills up you can see the fuel level in the clear pipe. Most bikes are set at 3mm from the joint where the bowl seats against the carb body.
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EvansWard
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Location: Macon GA USA

Re: Float height adjustment

Post by EvansWard »

Yep, that’s the ticket to getting those carbs to work as intended. And… for those on this side of the pond in the US, I have just a few left for sale too.
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1976 Suzuki GT750
1972 Kawasaki H2 750 Mach IV
1984 Yamaha RZ350
teazer
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Re: Float height adjustment

Post by teazer »

Paul and Evans are exactly right. Float levels are just a substitute for measuring the actual FUEL level and that is all you are trying to do. Some people are pretty good at getting the fuel level right by adjusting float level but most are a long way off. There are too many variables with floats including their weight and if they are slightly twisted or dented and so on.

Do the job sight and measure fuel level with an adapter and clear tube.
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