I've been foolin with the Rochester B on my 235, trying to get it running right, and I had a question that I just couldn't get over. Why is having the float level correct so important? I know that it will cause it to run rich/lean, but why? As long as the jet is submerged, and there is fuel to the accelerator pump. then why wouldn't it work? I have heard that it needs to be accurate to within 1/32" And how would changing the float level be any different than changing the jet size?
Well there's a few reasons it's important to have it set right. One of them is if you run it too low and you turn a corner hard, accelerate hard, brake hard, or climb a steep hill, it'll stall out on ya. Ofcourse if it's set too high, then it could overflow and the engine won't run right at all. As far as I know, float level doesn't drastically affect your mixture. It's just having the correct amount of fuel in the bowl so the engine doesn't stall out when doing any of the above. Also... in your scenario, if you just had enough fuel to cover the jet and keep it running... remember, that's only at idle. At full throttle you'd be out of fuel in exactly .0000012 of a second. I'm sure others will chime in with better advice than me, but that's kinda the jist of it. -Chris
The float level determines how soon the main jet feeds gas. Think how much easier it is to siphon gas from a full gas can than one that's half or a quarter full. That's kind of how a carb works, it's got to draw the gas from the bowl up to the discharge nozzle and down into the intake.
Air velocity past a pickup point in the venturi area causes a negative pressure in the fuel well. Atmospheric pressure in the bowl (the bowl is open to the atmosphere via the bowl vent) pushes fuel from the fuel well through the pickup into the venturi area. With the engine off, fuel in the fuel well will be at the same level as the fuel in the bowl. The level of fuel will alter the amount of negative pressure necessary to cause the fuel to flow. A good general rule is that a 1/16 inch change in fuel level is approximately equivilent to one jet "size". This approximation is good to know when "dialing in" a different carburetor, as it allows the tuner to "try" a jet size without buying the jet. However, don't try dropping the fuel level by more than an 1/8. And this change should not be permanent, only for testing. And CJ's reasons about stall, flooding, etc. are also valid reasons for maintaining the specified fuel level. Jon.
Jon, I didn't think about the effect it would have on mixture. Your post was enlightening and I learned a cool trick from it. Thanks! -Chris
Chris, you are welcome. Actually, this issue is much more complex than covered by this thread. Fuel level is directly effected by the float setting HOWEVER: fuel level is engineered by the carburetor manufacturer to be a certain level based on (A) the buoyancy of the float, (B) the height of the float arm in relation to the float pontoon, (C) the orifice of the fuel valve seat, (D) the pressure of the fuel pump, AND (E) the actual float setting. Lots of aftermarket parts vary significantly (either by design or "one size never works well") from the original specification. Example... many will add an electric fuel pump with great pressure and then add the dial type regulator (which basically doesn't regulate except at full flow) and wonder why the carb floods at idle. Same is true by adding a fuel valve with a larger seat orifice. And many of the aftermarket kits just use a fuel valve with an orifice sufficiently large to handle the largest engine for this style carburetor. A little homework by the enthusiast will have wonderful results. Jon.
Plus when you get a carb kit, follow the spec sheet and set everything as it say's, plus when it's apart, make sure all your passages are open and not plugged with dirt or what ever and use a good filter. A little particule of rust or dirt can foul things up in a hurry. Keep it clean and it will work.
Hey Boozer, how ya doin'? Do a search for the thread, tuning problems 235 Chevy six...and tuning problems Chevy six SOLVED! I went round and round with this myself, but with the help of some guys here, and one young local guy, solved the problem. The local dude actually explained it to me. As I understand it, there is a port that feeds gas to the idle-circuit. If the fuel level is not high enough, it never reaches that port, unless you over-compensate by choking the carb. Then, of course you start flooding the carb and fouling plugs. Check for vac leaks of course. Look close at the spacer and gasket under the carb. There should be a notch in the spacer, and a slot or hole in the base-gasket that lines up with the small hole (about 3/16 diameter) in the base of your carb. That little hole goes way up inside the carb to feed the vac signal to your idle-circuit. As others have said, if the float-level is too high, you'll flood and leak gas, but I think the most critical thing is to do with idle-quality. So...clean carb, good...no clogs, good...no vacuum leaks, good...(spray around intake and carb with carb cleaner, listen for change in idle speed) proper fuel-flow and pressure, good... correct flloat-level...good. Search the internet for an article on rebuilding the Rochester B carb...Rochester Carberator Rebuild - Fixing Broken Chains. Lots of good info. You'll see that he states that not only is the "float-level" important, but also what he calls the "drop level"...the level of the float when there is no fuel in the bowl. He shows how to adjust these and gives correct specs. By the way...if you don't happen to have the little scale (ruler) to measure with, transfer the exact measurement to a narrow piece of paper or thin card-board, and use that to measure. Be sure floats on both sides match. He shows all this. And...make darned sure you are reading your scale correctly! Good luck.--Rick
P.S. Boozer...if while the engine is running, your idle-mixture adjustment-screw makes a difference in idle-quality when turned, chances are that your idle-circuit is O.K. ........not the idle adjustment screw, but the idle mixture adjustment screw. You know...the one on the engine side. Start at 1 1/2 turns off of the seat. That'll get you close. --Rick
hey BOOZER...and i guess U are HA! just messing with U my brother. if the floot is to high, then gas will run over to the other side causing fluding. it has nothing to do with the jets. to low and u run out of gas when u put the hammer down. u dig? but 1/32 is nuts. call me POP...or the old FART!
Setting the "floot" level to specs is not "nuts". The manufacturers determine the specs, and they know a lot more about that particular carb than we do. If the specs say to set the float level to within 1/32", than you gotta know it's important, and should do that to the best of your ability. If you've had a few, or you're not paying close attention, you might get it to within 1/16". I think the manufacturers anticipated this...if they set the specs to within 1/16", some of us could be off as much as 1/8", and then you've got problems.
Thanks Carbking, Rickybop, and all others... Carbking - I'll be calling you soon to get a kit for this bad boy. I've heard nothing but good things about your kits/advice/service.... Rickybop - I browsed through your post when you were trying to get yours figured out. Thanks for the advice. The main problem that I'm having with my carb is that it wants to stumble choke and die when revved form idle. At first I thought that was my only problem, but after running it with the choke knob out a little I realized that it was generally underpowered and sluggish all the time, and I only noticed that something was wrong when I revved it. it idles great, and turning the idle mixture screw does make a difference in idle quality. That brings me to why I asked this question in the first place. I'm assuming that I'm running lean, so I was trying to decide wether to fiddle with the float level, or the jet size. I'm leaning toward float level.... more to come!
rebuild the carb then start fiddlin' with stuff that way you know the carb is within specs and clean so your not tryin' to over compinsate somewhere for a different problem. Getting a carb right Step one: rebiuld it. Seen people chase gremlins for days , little R&R and no more gremlins.
It's been thoroughly cleaned now (taken completely apart and soaked in berrymans carb dip for 24 hours) I'll get to rebuilding it soon. as soon as I get a good rebuild kit
The only caveat here not anticipated by the original engineers is the physical make up of the stuff they call gasoline. Which back then was pretty much gasoline, now it is a hydeocarbon soup made up of lots of different stuff. the result being that volitility (it willingness to evaporate) and other fluid dyamics are different. One consideration it to set the level a bit lower than spec to deal with hot starting issues, partularly perculation. Where the fuel in the bowl, sucks up heat (specially with a enclosed hood) and expands, boils over and floods the intake manifold with raw fuel, causing a flooded condition when you try a hot restart. I fought this for two summers before I lowerd my floats a couple hairs, then the problem went away. May have just been a coincidence but I have't had a problem for the past three years.
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