carb float

[kidkoh]

ok I bought a new carb and installed it for practice at nhis, every time i went into turn 3 ( hard breaks hard rt turn ) the car stumbled. I think that the float is not set right but I cant find any info on how to set the correct level. any info with the correct setup would be great. just a question I have the carb backwards with the float to the front, will that effect anything in a hard breaking area thanks for the help

[billinstuart]

I've seen soo many variations on floats, but it may be as simple as the level is too high or too low. Some swear by brass floats that don't pivot. It's been a few years, so I'm not sure what's this weeks hot carb set-up.

[SR Racing]

I don't know how your float was modified, or what else was done to the carb. BUT. generally you want the float fuel cut off point to be when the fuel is at about 5/16 to 3/8" below the flange. In most cases your symptoms indicate the problem is that the fuel is to high. It is now flooding the carb under braking or high G's. I would bend the tang or add washers under the valve to get it to shut off earlier.

If you have plastic float, it probably is modified to float upside down with a weight mounted to the original top of the float. You want it to weigh about 8-9 grams. (and of course no longer with the brass pivot arm on it.)

If you have a brass float, use it as normal but the tangs on the top should be bent back so as not to hook under the float operating arm.

Also.. IF you have to adjust the fuel cut-off by much, this will also effect the a/f ratio of the carb due to the changed level of fuel in the emulsion tube. ANd... changes in the mounting position of the carb (forward or reversed) and the bend at the manifold neck will all effect dynamic float level.

[njg005]

Jim
Out of curiosity, when is the fuel level in the bowl too low? In your book, I believe you had recommended the level should be between 9/16 and 3/4. Is this too low? At what level will you suffer from fuel starvation? What size needle valve do you recommend (1.5, 2.0)?
Thanks
Nick

[brian]

A common mistake in checking float levels is failing to remove the fuel line before removing the top of the carb. If you remove the carb top first, residual pressure in the fuel line will force more fuel into the bowl and mislead the viewer. If your car appears to flood after being shut off hot, the float is too high. After shutting off the motor, if you see fuel trickling out of the emulsion tube, your float is too high. If you feel cold water on your butt, your float is too high. The 1.5 jet should be adequate just make sure it's clean. Chack and make sure the accelerator pump is discharging a strong flow of fuel. I hate to admit it, but sometimes these old carbs get a stumble that won't go away. I suspect internal corrosion just like my arteries.

[SR Racing]

Jim
Out of curiosity, when is the fuel level in the bowl too low? In your book, I believe you had recommended the level should be between 9/16 and 3/4. Is this too low? At what level will you suffer from fuel starvation? What size needle valve do you recommend (1.5, 2.0)?
Thanks
Nick

Nick,

Actually the float level as far as running is not critical at all. As long as it is jetted at or near that level. The level in the float bowl will effect how the emulsion tube and air corrector jet function. It will work fine at most any level as long as it is jetted for that level. The problem come in with the dynamics of the track G forces. Most often the problem is that the G forces cause the float to rotate and not shut the fuel off. Most often under breaking or in hard g corners. This causes a stumble as it wets the plugs for a few seconds. I always like the float adjusted at the low end of the level. (less fuel in the float bowl). This problem can be compounded by a poorly designed float. One that rotates excessively or bounces around a lot. We (with plastic floats) counter weight the float with washer so that it weighs about 8 grams and floats upside down. This gives the best control of the shut-off arm.
Many people think and say that a flooding condition can occur when fuel escape from the bowl under the gasket and into the velocity throat. While it is possible. in most cases it is simply one of the above issues that is the root cuase of the problem.

It is also possible to have to LOW of a fuel level but it is far more rare. The symtoms can occur at the same time, but it is running out of fuel and not flooding. When this happens it usually corrects itself much faster. It is not often the problem.

When you do check the level follow what Bryan says above. Allthough I do have one differing opinion.<g>

In the pits when the engine is stopped. You will often have a slight bit of fuel that will trickle down the throat. This is due to the fact that a full float bowl level is slightly above the joint at the emulsion tube holder and base of the carb (and possibly the lower holes on the emulsion tube. These few drops will drip down onto the throttle plate and sometimes out the throttle plate pivot holes. Not a big deal since it will never happen on the track or when running.

Any ways, long post but other than jetting corrections to match the final float bowl level., it can be a matter of some experimentation to get the float level at the perfect point . The angle of the carb in the car and the forward or rearward mounting positions can make it slightly different on each car. In some cases, it will work fine on one track and not another.
Hope that helps.

[brian]

Good clarification Jim about the tube holder joint. If I am getting a leak at the joint, slightly expanding the brass tube with a punch will make it fit better and avoid the leak.