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Float levels suck....

tkent02

tkent02

Forum LongTimer
Past Site Supporter
1978 GS 750, C model.
Adjusted all the floats to perfection, 26mm exactly as per the Suzuki service manual.... Still runs lean. Made up a set of the little drain plug tubes to view the levels directly, they are all about 1/4" low, and they vary about 4mm between them. I can always redo the floats to correct for this difference but it seems something is not right in there. Any ideas?
Thanks!
 
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tkent02 said:
1978 GS 750, C model.
Adjusted all the floats to perfection, 26mm exactly as per the Suzuki service manual.... Still runs lean. Made up a set of the little drain plug tubes to view the levels directly, they are all about 1/4" low, and they vary about 4mm between them. I can always redo the floats to correct for this difference but it seems something is not right in there. Any ideas?
Thanks!
Click to expand...

Were your measurements taken with the gaskets on or off. You're going to get a slight difference between the carbs as they are rubber mounted and unless you've figured out a way to get them perfect in the boots, you will see a slight variation.
 
Gaskets were off....

Gaskets were off....

Just seems like too much variation...
 
tkent02 said:
1978 GS 750, C model.
Adjusted all the floats to perfection, 26mm exactly as per the Suzuki service manual.... Still runs lean. Made up a set of the little drain plug tubes to view the levels directly, they are all about 1/4" low, and they vary about 4mm between them.
Thanks!
Click to expand...

Ahhhhhhhhhhhhhhhhhhh. don't do that!! 1/4"low vary 4mm. keep with english or metric, please don't mix. gives me a head ache.
Set the float levels according to your fuel level tubes. Many things can affect actual float level. Float valves, float material, float weight, float absorbtion, etc. Adjust by your drain hose. Thats where ya wana be, regardless of float height.
 
Apologies....

Apologies....

nert said:
Ahhhhhhhhhhhhhhhhhhh. don't do that!! 1/4"low vary 4mm. keep with english or metric, please don't mix. gives me a head ache.
Click to expand...

The fuel levels are about 7mm or 8mm too low, and vary about 4mm between them.
Will adjust the floats to level the levels at the correct level today.
Thanks.
 
tkent02 said:
The fuel levels are about 7mm or 8mm too low, and vary about 4mm between them.
Will adjust the floats to level the levels at the correct level today.
Thanks.
Click to expand...

Lots of level'n going on there... Yep, can't go wrong using the tube method, it shows the true fuel height in the carbs regardless of any and all other factors.
 
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I'd be thinking seriously about a new set of floats, if I were you. I've chased similar problems in cars that turned out to be deteriorated floats.

Are your floats the round ones, or the ones with the step or notch in them? I think this applies only to CV carbs, but if the floats have a step in them, someone might have set these wrong by measuring at the top of the float rather than the step. That's probably not it in your case, but it's something I ran across on a friend's bike.
 
Like others said, a lot of things can add up to your results. Weak/cocked float valve springs is the most common. Checking with the tube and adjusting accordingly should help, but if the springs are weak, fuel metering will still be inaccurate due to typical road bumps/engine vibrations acting on the weakened valves.
Also, for what it's worth, 26mm seems a little high (lean) to me. I know you say that info is from a Suzuki manual, but something right in the middle of .90 to .98" is my opinion...94".
 
Got it working pretty good now...

Got it working pretty good now...

1 & 4 are perfect, 2 is a mm low, 3 is a couple low.
I'll get it right in one more try.
 
You can read the fuel level inside the float bowls...

You can read the fuel level inside the float bowls...

Drill four extra drain plugs lengthwise and put tubes in them, I used 1/8" drill and 1/8" brass tube from a model airplane shop. Epoxy the tubes in place in the drain plugs. I made the tubes an inch long, doing it again I would make two of them about four inches long to make it easier to screw them into the inboard carburetors. On one of my bikes the drain plugs are angled to the outside, on the other they are vertical so short tubes would be better. Put 1/8" I.D. clear plastic hoses on the brass tubes, screw the drain plugs into the floatbowl drains and fasten the hoses alongside the carbs. Clothespins or tape work fine. The ends of the hoses must be open for it to work, and must be above the level of the float bowl or fuel will pour out of them. You have just made a set of float level gauges.
Run the engine, choke must be off, let it idle. The fuel in the hoses will be at a level equal to the level inside the bowls. It does not matter how long or how big the hoses are, or how low they dip on the way to where you read them, the level will be the same.* Hold the hose close to the body of the carb, and measure the distance the fuel level is below the bottom edge of the main carburetor base, where the float bowl joins. On my 750 it is supposed to be 2.5mm - 3.5mm below the surface. Each model has a slightly different spec, there will be a picture in the manual to show you exactly where to measure it. If one or more carburetors is off, take the float bowl off, and correct the float level.

*Not sure but I believe a very tiny diameter hose may read too high due to capillary action.
 
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Build it yourself carb drain plug tubes!

Buy a 1' length of 1/2" (I think, its been a while) vinyl tubing (fuel rated preffered). The internal diameter of the tube should fit OVER the bottom of the drain "nipple" for your carbs (where the plug threads in).

Buy 8 hose clamps that fit over the 1/2" tube
Buy 4 Reducers from 1/2" -> 3/8" or something nice and small
Buy 4 hose clamps for the 3/8"
Buy about 10' of 3/8" vinyl tubing
Find a couple of zip ties in your garage
Find a small flat piece of wood in your garage

Assembly cut 3" pieces of 1/2" tube, cut 1', 1.5', 2' 2.5', 3' pieces of 3/8" (or something like that to compinsate for the carb spacing).
Assembly so that: 1/2" clamp, 1/2" tube, 1/2" clamp, reducer, "3/8 clamp, 3/8" hose.
Mount the 3/8" tubes on a piece of wood using the zip ties so that each tube is laying flat next to each other and with the carb tubes in order 1-4(draw some parallel lines on the board to make it easier to calibrate the floats)

This way, you have nice flexiable 3/8" main tubes so you can manuver the rig next to the carbs and see the levels of each carb. This rig only costs a couple of dollars, and should work on a variety of carbs as you don't need to hunt for special fittings to thread into the drain plugs...
 
I keep thinking I could just hook the carbs up to a fuel source on the bench and do the float levels, without having to mount/dismount them on the bike repeatedly. If the carb rack were oriented at the proper angle on the bench (as they are when mounted), is there any reason why that wouldn't work?
 
The level changes very slightly when the engine is running....

The level changes very slightly when the engine is running....

You could surely get it close that way, maybe close enough. I think fuel needs to be flowing, or maybe the vibrations are doing something. Give it a try?
 
tkent02 said:
You could surely get it close that way, maybe close enough. I think fuel needs to be flowing, or maybe the vibrations are doing something. Give it a try?
Click to expand...

That's pretty much what I was thinking.

The other thing would be since there's no gas flowing out (being sucked into the engine), if you somehow got too much in the bowls (tipping the rack?) it wouldn't equalize and you could get a false reading.

It'd probably get you close enough though. Undoubtedly closer than I am now. I have an extreme distaste for mounting the carb rack so if I can do it as little as possible I'm happy...
 
Bench checking/adjusting the levels would seem to be OK...but the factory says to check the levels with the motor running. I would only check the levels with it running too.
 
At least it would tell you if one of them was way off...

At least it would tell you if one of them was way off...

or two of them as in my case.
 
You know what would be really cool would be to replace a section of the bowl with something clear or translucent, like on a quart of oil bottle, so you could just glance at 'em and see the level. ;-)
 
I modified a spare bowl i had with a clear Mylar window. I scribed (2) lines through it for the high spec and the low spec. I set them on the bench and just move the "eye" bowl from one carb to the other. Never checked it running on the bike though. As far as checking them running, my thought is, great if you can do it. I just can't imagine on a hot 1100 engine, dropping the inner or outer bowls making a tweak, reassemble and recheck. Or removing the carb bank. I can see where actual running could affect fuel level cause by vibration, heat, angle, fuel use, etc. But i can't bring myself to attempt changes on the bike. I thought i was anal using a fuel bowl with a view. I think its more important that they are equal and within spec. If vibration can change it during idle, it will surely change with various RPM, vibrations, frequency, bumps, hills, and turns.
Having an external adjustment would really be great, like an automotive Holley carburetor. I can adjust my 66 BSA with twim Amal Monobloc carbs by changing shims on the fuel jet inlet under the fuel banjo.
 
nert said:
I modified a spare bowl i had with a clear Mylar window. I scribed (2) lines through it for the high spec and the low spec. I set them on the bench and just move the "eye" bowl from one carb to the other. Never checked it running on the bike though. As far as checking them running, my thought is, great if you can do it. I just can't imagine on a hot 1100 engine, dropping the inner or outer bowls making a tweak, reassemble and recheck. Or removing the carb bank. I can see where actual running could affect fuel level cause by vibration, heat, angle, fuel use, etc. But i can't bring myself to attempt changes on the bike. I thought i was anal using a fuel bowl with a view. I think its more important that they are equal and within spec. If vibration can change it during idle, it will surely change with various RPM, vibrations, frequency, bumps, hills, and turns.
Having an external adjustment would really be great, like an automotive Holley carburetor. I can adjust my 66 BSA with twim Amal Monobloc carbs by changing shims on the fuel jet inlet under the fuel banjo.
Click to expand...

A man after my own heart. Actually I think I probably heard about your "bowl with a view" before...

So how'd you do it exactly? Sounds like a handy "hack".
 
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