technical carb question (any bike)

I'm having crazy carb issues and I think it might be tied to the float level. So to correctly set my float level, I need to understand something about how a carb works: What is the ideal level for the gas to sit in the float bowl?

See attached drawing -- I proposed 3 different levels. Which is ideal?




Re: technical carb question (any bike)

ummmmmmm the second i guess

Re: technical carb question (any bike)

Oh yeah, there's a part 2 of that question:

Is having it at one of the two levels that is not ideal going to prevent the bike from running properly?


Re: technical carb question (any bike)

wow, i like your drawing a lot, its quite nice

Re: technical carb question (any bike)

thanks for the input, brett.

Re: technical carb question (any bike)

i would try it at setting one first, with the highest level, and work my way down. i prefer when they run lean. after each adjustment, take it for a long ride.

Re: technical carb question (any bike)

your bike should be able to run at WOT on a full bowl of gas for maybe 15 seconds. give or take a few. your fuel should feed into the bowl faster than the jet sucks out gas.

one way to test how much your float is allowing you to hold is to rinse the carb so you dont get gas in your mouth. fill your mouth with tap water and then force water throug hthe banjo bolt. when you cant blow any more water it is then that the float is fully engaged. carefully take out the bowl and see how much water is in there. that way you can see how much the float allows you to keep in. i know this way sounds really stupid and primitive. but its much harder to do this while its on the bike because takeing the carb out usually means you have to tip it over at odd angles and you lose alot of the gas out of the bowl.

another thing to do is to time how long it can run on a full bowl of gas.

you can turn off your petcock and take out the fuel line out of the carb so the residual fuel doesnt come back in. make sure you dont tip any gas out of the bowl.start it up and run it at wot and time how long it runs before it dies.

then i guess you can somehow time how long it takes for gas to fill up the bowl. the time should be less than how long it takes to run at wot before dying (the test you did just before)

ok well those are just ideas and i think they make sense. i just pulled all that out of my ass and its silly but it might answer your questions. i have actually tested to see if a float is functioning with a mouthful of water over the banjo bolt

Re: technical carb question (any bike)

well, i can't get it running well enough to take it for a long ride. i can get it started at full throttle, but as soon as i let go, it dies. or i can get it running at no throttle, and as soon as i give it any throttle it dies.


Re: technical carb question (any bike)

oh yeah and make sure you always do those tests with the carb leveled out

Re: technical carb question (any bike)

doesnt sound like it has anything to do with the fuel level. have you thought of jetting? maybe you are under or overjetted. try taking out the airbox and seeing if it runs better. use your finger as a choke then see if it runs better. maybe somethings up with your electricals and the higher rpms generating more electricity to the bulb and headlight are taking away power form the ignition coil.

what sounds does it make before it dies? now if you REALLY insist that its your float then try running without a float

yes i know you're gonna make a mess when the petcock is on but its worth a try.

these are all just thoughts.

Re: technical carb question (any bike)

when i leave the petcock on PRIME, it always overflows the carb. so i'm guessing the float valve isn't operating correctly. it's a new valve and stopper, so it must just be the float level it's set at, or the floats themselves not floating.

i put a battery in in case it was a voltage thing, but that had no effect, the battery has very little charge, but still, it didn't change anything at all. and it runs at full throttle, so that's probably not it anyway.

there's some sort of fuel pump contraption that's part of the petcock. the fuel line comes out of this, as does an air line that connects to the top front (engine side not air filter side) of the carb bore. i want to bypass the petcock/fuel pump, but to do so I need to get the float valve working so that it will fill up the carb without overflowing it. it seems like that's the way it should operate anyway. right?

thanks for your help. see you at that boston ride if it comes together.


Re: technical carb question (any bike)

take your carb off and then take the bowl off turn it upside down and if the float sits level then its fine if not adjust it to sit level

this has always worked for me so i hope if works for you


What is your actual problem ?

Carburetor float levels are typically dictated by the

manufacturer - in the repair manual.

If the level is set too low the bike starves for fuel,

especially at higher speeds. If the float is set too

high, the fuel runs out the overflow drains.

What problem are you having?

And on what bike?



Re: What is your actual problem ?

yeah! if you come ride in boston message me and we'll go riding. usually if its an issue with gas you can hear it bog or something. whereas when its electrical it might just die.

i dunno about your fuel pump contraption but you can try to make an auxiliary tank using a bottle and fuel line. and if you wanted to you can squeeze gas in and force it.

WAIT weird. you can start it at full throttle but cant lower it and you can start at idle but cant open it? that sounds like you have something up with your mid messed up. ive only worked with bings but have you check to see if your needle is messed up? or adjust needle height

my actual problem


i can get it started at full throttle, but as soon as i let go, it dies. Or i can get it running at no throttle, and as soon as i give it any throttle it dies.

That's the short version.

Suzuki FA50.


Re: my actual problem - 2

I would first check for a vacuum leak. If it will run at idle just

use an un-lit propane torch to put propane around the carb (not

the throat - although doing that will show you what you are

looking to happen) and the intake manifold. Any increase in

RPM indicates a vacuum leak.

Does the throttle cable on this carb directly raise the slide/piston

in the carb? OR does the throttle cable open a butterfly and then

the reduced vacuum in the carb body raises the slide/piston?

I ask because sometimes those vacuum actuated slides stick and

give you weird throttle response.

Is the carb absolutely, perfectly clean inside?

Another thing to check is the ignition advance mechanism if

there is one.

BTW: there is an old saying in the motorcycle repair business:

"About 90% of carburetor problems are electrical." <g>



Re: technical carb question (any bike)

if you have a vacum operated petcock with a prime setting, will it run just on prime?

it kind of sounds like you have a mix of problems, it sounds like you have either a bad vaccum line, or a stuck diaphram, at least from what I've seen of vaccum operated fuel valves, those are commen problems, the idea behind them is the engine vaccum keeps the fuel valve open, so when you turn the engine off, the fuel turns off as well, your WOT is producing more vaccume, thus keeping the fuel open, option number 2 is that your float hight is to high, to find this out, fill up your carb then turn off your fuel compleatly, then start it up and run it untill it runs ok, it will take about 3 minutes for it to use up all the fuel in the float bowl, as that fuel leavle goes down how well it runs will change, if it just keeps getting worse till it dies, then it's to low, if it gets better, then runs really good for a minute, then slowly dies, then it was to high, and the running really good was where the fuel leavel was correct.

I would never put water in a carb, if you do, wash it out with carb cleaner, every single little nook and cranny, a drop of water can give you problems for weeks.

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