Topic: Float settings

[750 Blaster]

 In the process of rebuilding my carbs for my '74 750 I noticed all for floats were set at about 3/4"  measured from carb body. However Clymers say setting should be 1.023" or over 1/4" from were they were set!
 Any ideas were the bust is?

[iron_worker]

26mm or 1.023" is correct if you have the correct carbs on your bike.

Is there any numbering or stamped into your carbs like 657A or similar?

Also, a PO could have adjusted the floats in an attempt to tune the bike for mods that were made. Does the bike have stock exhaust and airbox?

IW

[flybox1]

intake and exhaust mods really dont have anything to do with float height.
fuel level is fuel level, and there's only one right one.
you're not gong to be able to properly/adequately tune intake and exhaust mods with float level adjustments. you need to make jetting and needle clip position changes.
but yes, IW, the PO could have changed fuel level thinking it would help, or fix an overflowing carb.

[iron_worker]

I'm sorry but that is incorrect.

Fuel level has very much to do with mixture. You can tune your mixture with fuel level, however, you end up increasing or decreasing your mixture over the entire range.

The lower pressure created by the acceleration of the incoming air into the carb throats "draws" fuel through the jets... or rather since the bowls are vented to atmosphere, the higher atmospheric pressure pushes the fuel up through the jets.

The amount of fuel that makes it through the jet is depending on a few things ...

1)The specific gravity of the fuel and the viscosity (factors that we will assume to be constant and not "tunable")
2) The inside diameter of the jet and fuel passage
3) Height that the fuel must be raised from fuel level to carb throat ... the overall length of the passage also has a friction effect but is a much smaller effect than the height difference
4) The roughness of the inside of the jet (also not tunable ... realistically)

So if you increase the diameter of the jet, you decrease the amount of friction or resistance to flow. Thus, given a specific air velocity/carb throat pressure you will get more fuel.

Likewise if you lower the fuel level you increase the distance that the fuel must be raised up to the carb throats or vice versa and you will get less fuel for a specific air velocity/throat pressure.

IW

[flybox1]

IW, I agree with you 100%, I wrestled with this very issue on my 350F, but for the purposes of the OP sorting out carb and tuning issues on a new bike, the biggest effects he can have on getting the mixture close is with stock float setting, with jets and needle settings to match his intake and exhaust.
i guess i didnt want to inundate the newbie with overly detailed information....i let you do it 
you did it well, too 

so i'll modify my previous post, so its not so black and white 

[greenjeans]

26mm from the base (where the gasket goes - not the lip that extends)

You can make a gauge out of an old credit card.     I usually clamp mine  at an angle where the float tab doesn't rest on the float needle.

Double-check those float needles while you're in there - those are crucial.

And finally, check the actual level of fuel once they are back on with the "clear tube method"   You can do a search for that.   Basically, you're just using clear tubing coming from the float bowl drain screw.  That way you an see what is actually going on.   Very accurate.

[iron_worker]

IW, I agree with you 100%, I wrestled with this very issue on my 350F, but for the purposes of the OP sorting out carb and tuning issues on a new bike, the biggest effects he can have on getting the mixture close is with stock float setting, with jets and needle settings to match his intake and exhaust.
i guess i didnt want to inundate the newbie with overly detailed information....i let you do it 
you did it well, too 

Haha ok maybe you're right. It could have been too much too soon. 

Flybox is right. Stick with the stock float level as per the manual and adjust your mixture using idle mixture screw, adjusting clip position on needle jet, and chaging pilot or main jet sizes. This way you can tune in each throttle position individually as needed.

IW

[lucky]

Just set the floats the way the workshop manual shows.

Forget all the other stuff.

[scottly]

And finally, check the actual level of fuel once they are back on with the "clear tube method"   You can do a search for that.   Basically, you're just using clear tubing coming from the float bowl drain screw.  That way you an see what is actually going on.   Very accurate.

1+

[Jerry Rxman Griffin aka MuthaF'er]

I don't agree that the float height should be set from the gasket base/surface. Kinda like an oil thread, huh  That is, if by "26mm from the base (where the gasket goes - not the lip that extends)" you mean to measure from the deepest part/bottom surface of the 'slot' the gasket fits into the carb body.

I have a Honda Universal Float Level Gauge. Part 07401-0010000. It has a float height list with it that provides measurements from the 50's to 750's. 2 of my manuals say "float bowl mating surface". Not very clear description. None of the pictures show the later style tool either and none of the pictures are clear but the picture that comes with my tool is the best and it could be better. My carbs from my 75 750F have indentions of about 1/2" long on both outside surfaces that are below the lip and centered on each side and centered to the floats. This is about the height the float bowl mates with the gasket. Do the earlier carbs have this?? I can't say. There is no way my float tool is designed to fit inside that 'slot' as I call it. ie at the base/bottom of the gasket surface. The legs of it are too wide.

My contention is that the measurement using my Honda factory tool is to be accomplished by placing the measuring device within these 'indentions' on the sides of the carb body and perpendicular to the carb body.

Anyone else have any thoughts? What about your Honda tool? Do your carbs have the 'indention' I'm referring to?

[lucky]

I don't agree that the float height should be set from the gasket base/surface. Kinda like an oil thread, huh  That is, if by "26mm from the base (where the gasket goes - not the lip that extends)" you mean to measure from the deepest part/bottom surface of the 'slot' the gasket fits into the carb body.

I have a Honda Universal Float Level Gauge. Part 07401-0010000. It has a float height list with it that provides measurements from the 50's to 750's. 2 of my manuals say "float bowl mating surface". Not very clear description. None of the pictures show the later style tool either and none of the pictures are clear but the picture that comes with my tool is the best and it could be better. My carbs from my 75 750F have indentions of about 1/2" long on both outside surfaces that are below the lip and centered on each side and centered to the floats. This is about the height the float bowl mates with the gasket. Do the earlier carbs have this?? I can't say. There is no way my float tool is designed to fit inside that 'slot' as I call it. ie at the base/bottom of the gasket surface. The legs of it are too wide.

My contention is that the measurement using my Honda factory tool is to be accomplished by placing the measuring device within these 'indentions' on the sides of the carb body and perpendicular to the carb body.

Anyone else have any thoughts? What about your Honda tool? Do your carbs have the 'indention' I'm referring to?

Just look at the photo (fig 13) bottom of page 125 Clymers' shop manual.
It is just that simple.

[Jerry Rxman Griffin aka MuthaF'er]

Or page 80 Chapter 6 and page 23 (the best) & 24 Chapter 2 in my Clymers circa 1976. Good snag Lucky. That's the clearest picture yet and the same tool I have. It shows measuring from the outside rims in the center. My page 125 is shocks.

[750 Blaster]

The discussion between IW and Fly is very helpful, thank you brothers. (I'll ignore the newbie remark :-) I did measure from the correct place, so thanks to all for your comments, very helpful also.
 The bike does have the orginal air box, but PO installed 4-1 Magaphone exhaust. He may have changed the jets, I'll have to check on that. But could my following assumption be correct:  If the PO installed larger dia. jet, he may have discovered he needed to raise the float level from the standard 1.026 to about .75 to try to reduce the fuel pressure....is this a possibility?