Understanding Carbs 101

[Hired_Goon]

Ok, slightly cryptic title to drag your attention in here for my question.

Been having a discussion with a mate on the difference float levels make to rich/lean conditions.

Now I've never paid much attention to float levels as I've always seen the floats as a simple fuel delivery device to keep things running.

Ie Set too low and run out of gas at WOT

And set too high, flooding, stains, pool on the floor etc.

Now to the hard part of my comprehension.

How does 1-2 mm make a difference in a carb bowl that is essentially sealed from the carb throats with the exception of the main jet and starter tube.

Now both of these fuel intakes are taken from the bottom 5 mm of the bowl so I don't understand how a few mm on the level can make a difference.

Lifting the fuel level still means the feed has to go through the main/pilot jet orifice so why does it make a difference.

Cheers
HG

[renegade_xs11g]

I happen to be of the same opinion...

at least on the float adjustments...

I just rebuilt the carbs on my 80 'G' model,
I left the height alone on the floats because I never had a problem with running out or over flowing,
but had to stop while sync'ing, wife's cat hit by car, had to put her down, out of daylight when I got back.

I guess time will tell.

REALLY interested in what the GURU's will chime in with,

Very interested indeed

Thanks, John

P.S. Put the CAT down, NOT the wife.
Just wanted to clear that up!

[TADracer]

Put a drinking straw in a glass of water and blow across the top. With the straw high out of the top of the water you will get very little flow. Now cut the straw off so it is near the top of the water and blow again and the water will flow freely.

Same thing in the carbs. The closer the fuel level is to the top of the emusion tube the easier the gas will flow out of the bowl and into the airstream. So float level has an effect on idle, mid range and WOT.

The sweet spot for my special is 27mm. 29mm and it is rich....25mm and it seems to starve.

[prometheus578]

Dadgummit, TADracer....

(why is it that everyone wakes up earlier than me and posts the easy answers all the time?)

Now both of these fuel intakes are taken from the bottom 5 mm of the bowl so I don't understand how a few mm on the level can make a difference.

Yes, the fuel gets drawn from the bottom of the bowl, but the floats determine how high up the emulsion tube the level is. As TADracer mentioned, the higher up the tube, the easier it is drawn into the carb throat.
Jet size determines flow rate... how quickly fuel can get back into the emulsion tube to replace what is being used. Larger jet, more fuel... fuel being replaced quicker in the tube so that there's no starving/lean condition.

[Hired_Goon]

Ahh, thats what I love. Simple answers in a nutshell that I can understand.

Was worried I might be in for a physics lesson.

This helps me understand the problems I'm having a little better.

Thanks , I now know the next course of action to get rid of the faltering I have. (on the bike)

[mro]

physics lesson

Nope....fluid dynamics and chaos theory


mro

[Douglas Money]

I am still learning. I replaced the needles and seats and gaskets. The carbs poured all over. Of course they didn't with the old parts. So off with the carbs and reset the floats. Now it doesn't want to run. I'm getting tired of them already. My wife keeps asking when we are going to ride and I have no time to work on it and not much more motivation to touch it. I felt it was going to be a bad thing when I tackled it and I appear to have guessed right. I can pull them apart again, but now that the floats are set dead on, it's anyone's guess what is wrong. I still feel I should have left well enough alone. I had a choppy midrange before I did this.

[Douglas Money]

BTW, if someone in the Chicago area would like to earn some money and show me what I need to do, I'm interested.

[prometheus578]

Douglas,
Pull the carbs once again. this will be the last time.
remove the float bowls. Turn the carbs up-side-down in one of your wife's baking pans. Place your fuel tank on a milk crate above the carbs and hook up the fuel line. Turn the petcocks to "FLOW". "Blip" the floats to remove trapped air in the lines, and then dry the area of the needle and seat.
Sit and watch to see if, or where, the fuel is leaking from.
If it doesn't leak, reset the floats, put the carb bowls back on, turn the carbs right-side -up and "bench test" them again. If they're gonna leak, it'll come out of the main jet emulsion tube, or from the air jets in the carb bell on the airbox side.
Write back with the results and then we'll move on.

[underdog57]

Doug ,
One other thing is the jet needle , the one that goes in the emulsion tube can get worn . That will do the warbling at mid range ... you get black plugs ...look for worn brass color , it is shiny silver if they are worn ...mine are shiny silver and pitted.

Good luck and I know how frustrating this is ...Especialy not knowing all the details of what to look for...
Plenty to learn ..

If I'm wrong , feel free to sqaush my post ...

Bob

[Douglas Money]

Prom, this is the same procedure that I did before I put them back on, but I'll try it again. I made sure they werent leaking on the bench upside down hooked to a tank. I carefully rechecked and adjusted the float levels back to 25-26mm. They were more like 27-28. I made sure all were at the same height. I do appreciate all of your help.

Thanks,
Doug

[Douglas Money]

Underdog, the warbling problem was previous to me replacing the needles and seats. Now, it just doesn't want to stay running. It runs horribly and almost as if it needs more fuel.

[skids]

Is it otherwise bone stock? Does it flood only when running or only when sitting? 79 vintage carbs and box?

Originally posted by Douglas Money
BTW, if someone in the Chicago area would like to earn some money and show me what I need to do, I'm interested.

[Douglas Money]

Yes, I bought it in 2005 and it ran fairly well. Good gas mileage. Just the warbling on accelleration in upper midrange. I decided to go through the carbs since they needed it. The needles were the old steel ones not the vitons. After a couple of times of having them on and off, I have it running. The first time they started pouring gas as soon as the prime was turned on. So I reset the float levels and that took care of the flooding problem. I feel that I may have them too low. I am in territory unfamiliar to me. I have been told that the fuel bowls and the carbs are not the same year. I can take pictures later today if that will help.

[Douglas Money]

Also yes it has a stock airbox.