Adjusting Float Height theory and practice.

[chance johns]

I'm having an issue with this, i am seeing conflicting theories and practices.

This is my understanding of the adjustment of floats.

You bend the tang to shut off the fuel flow via the float needle. to have an optimum fuel level in the float bowl so as to not deplete the reservoir under max load. Also to not let the fuel level raise past the mating surface of the carbs.

i see people say of your bike will run lean or rich if your float level is off. this doesn't sound right to me. the only way it could be a lean scenario is if the fuel level was shut at a perfect level of what the bike was asking for. giving enough fuel to run and not bog down but causing a lean mix from there not being enough fuel at the level that is needed. NOT A LIKELY SCENARIO.the only way rich is if the fuel level is above the mating surface and leaks into the carbs but that fuel probably wouldn't be atomized and ignite anyway. it can't be lean or rich because its all getting sucked up through the fuel jet and there either is or isn't enough to run at a given load.

somebody clear this up?

also the adjustment. the manuals say, with the carb upside down,measure from the mating surface,with gasket in place, to the top of the float.

People say, you should start your measurement from just where the tang starts to touch the top of the float needle.
which is actually a very different measurement then what the manual suggests.



my carbs are leaky. i set them to spec from the mating surface with gasket to the top of the floats(27.5mm), just to where the tang starts to touch the float needle, and it still leaks. spring is springy in the float needle, but seems a little weak maybe. needle seat seems just fine.

also it appears as if one of my carbs. the one that leaks the most, has an aftermarket needle seat and needle. the needle is shaped a little differently and the spring is a hell of a lot stronger than the other two. I've read to set an aftermarket needle at 26mm. that would make it shut off later than the stock needle. i set mine to 29mm and it still pours like a sieve.

im testing all of this either with an external fuel tank or on the bike with the fuelcock in the prime position.

so, heres my questions.

-if you adjust your float height to spec and it still leaks, does that ultimately mean your float needle is bad? (assuming floats,float and the float pin isn't bent and hanging up) ( with the fuel line on the carb and float bowl off i can shut the fuel off by moving the floats by hand.)

-can you visually tell if your float needle is bad? besides imperfections to the conical tip.

-what is the proper technique to properly adjust the float heights, from the different ways i described previously.

-where can i get a set of oem needles and seats? knk?

thanks guys. 4 years and 4k$ into trying to figure out this puzzle of a GT

[ConnerVT]

Leaking carbs. Carburators should not "leak". The fuel level of a filled float bowl is (well) lower than the top of the float bowl. For a carb to leak, there would need to be either an opening (hole/crack) in the float bowl, or the carb tipped to the side enough to allow fuel over the edge of the bowl.

The fuel is coming out somewhere. But the question is - where? Is it coming out of the vents/overflow? Or are you just seeing/smelling random gas stains on things. I once had a leaky petcock (external leak) which dripped down the outside of the fuel lines. Swore for weeks it was the carbs leaking.

But if the fuel is actually going into the carbs, and then coming out, the first suspect is the float/float needle/needle seat. Its primary purpose is to stop the flow of fuel once the fuel reached the prescribed level. And that level is below the top of the bowl, so it shouldn't be leaking fuel (see above).

Floats with a pinhole leak will sink, not allowing the needle to close at the ppropriate level. A marginal surface (dirt/scored) on the needle or the seat will allow fuel to pass when closed. A damaged gasket between the carb body and seat could also do the same.

Different manuals describe different procedures for adjusting float height. A personnally agree with the one that says to hold the carb on an angle when taking the measurement. The reason is due to wear of the spring in the float needle. If the needle was solid (no spring), it really wouldn't matter how you held it, But the weight of the float can compress the spring (especially if it is older than new) which can affect your float level.

[chance johns]

my carbs are leaking from the float bowl mating surfaces. and vent. i realize its a float adjustment or needle situation. my questions remain the same. thanks for the response.

also can somebody describe the purpose of the springloaded float needle. im more accustomed to a float needle with rigid top and rubber conical tip. it make sense to me that pressure from the float seals the seat with a rubber/brass seal from the needle / seat. why is is there a metal to metal seal supposed to happen and why is the top of the needle spring actuated?

[ConnerVT]

I'll speculate that the spring is there to dampen the effect of vibration, reducing small flows of fuel, and helping to preserve the tip of the needle.

Why isn't the float needle viton tipped? Probably cheaper to produce, and the engineers probably felt it would wear longer. Along with the (then new) vacuum petcock, they likely weren't concerned with smalla mounts of leakage when the engine was off - the needle would seat well, once the float bowls were sufficiently filled.

[Coyote]

Plain a simply, your carbs are overfull by the thickness of your bowl gasket. NO GASKET when setting float height.

[ConnerVT]

my questions remain the same. thanks for the response.

-if you adjust your float height to spec and it still leaks, does that ultimately mean your float needle is bad? (assuming floats,float and the float pin isn't bent and hanging up) ( with the fuel line on the carb and float bowl off i can shut the fuel off by moving the floats by hand.)

If you hold the needle into the seat, and it still leaks, either the needle or seat is most likely bad.

-can you visually tell if your float needle is bad? besides imperfections to the conical tip.

If you have really good eyes (or a magnifier), you might see what is preventing it to seal. The needle or seat could also be out of round.

-what is the proper technique to properly adjust the float heights, from the different ways i described previously.

I prefer adjusting at an angle, as opposed to completely inverted.

-where can i get a set of oem needles and seats? knk?

I'd also check Dennis Kirk (where I get my T500 brass) and Jets R Us.

[chance johns]

well, i would naturally adjust float height without the gasket but i seen people say to do it with. there are so many conflicting accounts, and thats why im here. to get to the bottom of it! my fuel flow DOES stop when floats are acuated manually.

[tz375]

The best way to check fuel level is to do it "wet". Float setting is just to make life easier for us to do without getting soaked in gasoline.

Make a new bottom bolt for the carb and attach a length of clear tube to it. Bend that tube upwards and find a way to fill the carb from an auxilliary tank and measure where the fuel is in relation to that gasket surface. The norm is 3-4mm below the carb bore.

If your carbs are leaking from the float bowl gasket the gasket is not sealing and the float valve is probably seeping fuel as well.

Fuel height makes a difference because a higher fuel level exerts more pressure on the main jet which allows additional fuel to flow.

[chance johns]

exerts more pressure on the main jet? how? i would like to hear more people touch on the rich/lean theory of carburetion in relation to float adjustment.

[Coyote]

Atmospheric pressure / gravity. Richard, I would think the difference would have to be miniscule in say 1mm higher level. Of course I didn't pay much attention in chemistry. There was this girl..............

[tz375]

I know it sounds too small to be relevant but think of it this way 10mm of fuel will exert a certain pressure on whatever is at the bottom of it. 20mm of fuel will double the pressure and so on. It's close enough to a linear relationship.

So 1mm change in 20mm is 5% difference in fuel pressure. air flowing through the carb bore is subject to Mr. Bernouli's wicked little theorem and as it speeds up through the venturi, the pressure differential between the fuel in the bowl and the air in the bore causes fuel to rise up through the main and needle jets.

I would expect that at speed, that 5% change in pressure would result in a 4-5% change in fuel flow. With say a #100 main jet, that's the same as moving to a #105. The effect on slow to mid range will be larger and on top end smaller because of air mixing with fuel.

[r3tro74]

I made up a float height gauge like shown here: http://kawtriple.com/mraxl/tips/floatgage.htm" onclick="window.open(this.href);return false;
You'll have to size it to your specs. Notice the notches to clear the gasket surface ribs. I cut it a bit undersize then used a file to fine tune to exact size. Works good because you don't have to line every thing up trying to eyeball level across a ruler and the roundness of the floats. Also it sets all carbs the same.

[oldjapanesebikes]

well, i would naturally adjust float height without the gasket but i seen people say to do it with. there are so many conflicting accounts, and thats why im here. to get to the bottom of it!

Chance - why not check the relevant Suzuki manual and see what it says ? And to save you some time - in the carburettor manual it does clearly say, measure without the gasket. You can find it at this link. You can also refer to Specification #6, (page 5 I think) which gives the specifications for the 1972 carburettor settings (your bike is a 'J' ?) - in the footnote at the bottom of the page where it says to measure from the gasket fitting surface, not from the gasket. The link to that information is here.

About fuel bowl leakage - have you checked that the bowl mating surface is actually flat ? After a few decades, what happens quite often is that the bowls get deformed by the pressure of the screws at the four corners, so that only the four corners are actually tight which then can be a cause of leaks. You can sometimes fix this - if this is actually the problem - by lapping the bowl mating surface on a piece of plate glass and some 2000 grit wet and dry paper. I usually use WD40 as a lube. Worth checking at least.

[chance johns]

i reset the floats and all seem to be good except my left carb. that is the one with the newer looking float needle. but also i have one hell of a lean on the side stand, so that could also be the issue. trying to go through this over heating issue now.........