Conflicting info on SU fuel level.

[dbrick]

I read the FAQ on float level setting. 311s FAQ says 1/8 drill bit across cover, I assume without the gasket. The Chilton book I have states 1/2" from top of float to cover, inverted, tab just touching needle valve stem, rebuild kit says either 13/32 or 9/16 depending on the year, same way. Rather a big spread of measurements. With the piston removed, looking down the jet, fuel level is even with the top of the jet at FULL CHOKE, jet down. This doesn't seem right. I may just have to call Keith and get the rebuilds.

All help appreciated.
Thanks

[S Allen]

Cannot remember where I got that from but if it is wrong I will fix it.

Steve

[dbrick]

I'm hoping it's right, following the other specs seems like a low fuel level

[RoadsterYosh1]

I did the drill bit thing too, pretty sure I went ¼� measuring from the cover to the “metal� part of the float not the top of the plastic float its self.

Something to think about, when I took apart my carbs I had 2 different types of needle seats and both floats were set different. Replaced them with same new ones. I too though ½� was too low of a setting, eyeballed it till it looked right, then measured it to do the same for the other carb.

hope that helps.
yosh

[spl310]

I recall some discussion about this one time, and the most logical answer was to run the car and stop it. Then remove the suction piston chamber and pull the choke cable. If the fuel level is right at the top of the jet bore, then you are in business. If fuel is slobbering around, then it is too high, if the fuel level is substantially below the top of the jet bore, then it is too low.

[dbrick]

I have an electric pump, so I let it run, fuel level is at the top of the jet tube when it is retracted at full choke. So to be correct, I need the fuel level to be at the top of the jet in normal running position? This would put the fuel just below the "floor" of the venturi? So I need to raise my float another 1/4 to 3/8"almost to the top of the cover. Am I reading this correctly?

Just want to be sure, those gaskets are getting tired of being removed.

Am trying out a Color tune, Very nice tool, easy and accurate.

[spl310]

Dave,

I suggest that you contact Keith. I think he was the one that posted that info, but am not 100% sure. Either way, he is Mr. SU...

[RoadsterYosh1]

Don’t get discouraged, this is part of the fun of owning an old car! I really enjoy tinkering on this car.

Here’s how I set my floats:

1. On the outside of the float bowl measure from the top 7/8� and 1� draw a pencil line at those 2 points.
2. remove the fuel transfer line from the bottom of the bowl and replace it with a 6� or so length clear plastic hose (aquarium air hoses works well, but don’t use as a permanent solution)
3. rough set your float by the drill bit method.
4. reinstall the float to the bowl, complete w/gasket,
5. crank the engine (removing the coil wire and spark plugs helps) make sure the open end of the clear hose is above the level of the float bowl.
6. check the height of the fuel in the bowl by placing the clear plastic line next to the bowl. The fuel level should be between the 2 lines marked earlier. If not remove the float and adjust accordingly. I try to adjust the fuel level just under the 7/8� mark. At no time should you have the fuel level above the 7/8� mark, as the needle seat gets worn, the fuel level will go up and may leak out the carb.
7. reattach the fuel transfer hose.
8. do the same to the other carb.
9. I adjust the mixture screw out to 2 ½ turns as a starting point, then fine tune.

It just takes time and a bit of patience.
good luck
Yosh

[JoeK]

Well, we all have different ways. I have heard of Yoshis way, and it seems like it would be the most accurate. This is how I do it, and I think it is a little easier. I take the float bowl tops off and flip them upside down. The floats should rest on the overflow valve. To set the floats, I hold the float so that it is just toching that valve tip, and using a 9/16" feeler gauge (I actually use a carpenters pencil), pass it between the float and cap. Make sure your feeler gauge spans all the way across the cap. The idea is that when the float is sitting square, it should be 9/16" above the rim of the cap, with the tab that pushes the valve closed just barely touching the valve.

I've also heard a few British SU old timers say that float bowl levels don't really matter, as long as the carb doesn't runneth over.

[dbrick]

Keith is providing tech support, Unisyn is in the mail, Loaned mine to someone 20 years ago, haven't seen it since. Looks like the level is good, so sync and go