48 IDA Float Settings

[jhirasak]

I recently decided to check my fuel levels in the bowls since I still had some slight coughs and exhaust pops during the slow speed and cruise RPM range. Typically, when a Weber spits back it is an indication that the AFR is slightly too lean while a pop out of the exhaust indicates that the AFR is slightly too rich. Since the size of all of the jets were the same in each carb, it made me wonder if my fuel levels were the same on all of the carbs. To check this, I purchase a sight glass gage from Bieker Engineering who produces a very high quality product (however it is quite expensive). Upon taking measurements of the current fuel levels, I found a +/- 4mm variation from the average fuel level.

It seems that my initial static float level settings were inaccurate when I first set them up. When I measured the distance (24.2mm) from the top of each carb body to the float tang, I did not take into consideration where the needle seat should contact the tang.

To correct the individual fuel levels in each carb by using the sight glass gage, I built a tool from a long piece of 1/4 in. steel rod by cutting a small notch at one end with a die grinder and thin cutting disc (see attached photo). By using this homemade tool, I was able to adjust each float tang so that the final fuel levels were within 1mm of each other. This seems to have gotten rid of those irritating coughs and pops in the low speed and cruise conditions. I would recommend this procedure for anyone with 48IDAs that has minor hickups under low speed and cruise conditions

As a double check, I plan to reinstall my wideband O2 sensor and check my AFR over the entire operating range.

An alternate method to check the fuel level in each carb is to use static fuel level measurements instead of a sight glass gage (it is also a lot less expensive). To do this,is shut the engine down after it has been idling for a while on a flat floor and remove each of the carb bowl tops to measure the distance from the carb body top to the level of the fuel in each bowl. The advantage of the sight glass method is that it allows you to observe the fuel level while the engine is operating.

I would be very interested to know if another owner of a 48 IDA Weber equipped vehicle encountered the slight miss-fire symptoms that were similar to mine and found the cause to be due to variations in the fuel levels in the carbs.