I have dual webber 40 IDF, the carb was leaking through the accelerator pump diaphragm. After replacing it the carb over flows throug the top? I checked the needle valve and it moves freely and is attached to the floats. The floats also move freely. Could it be the floats need to be adjusted, if so how.

If the floats are properly set per Weber and the needle valves seem to be
aligned correctly, it should not overflow. Check to see that you are not pushing more than about 2.5 psi fuel pressure.

You can significantly improve the carbs by installing Gross Jets by D&G Valve, I think,
in place of the needle valves.

Phil

Floats might need to be adjusted or perhaps the needle valves
are shot, but how's your fuel pressure?
If its too high it will overpower the floats and needle valve which
would cause fuel to boil over from the middle of the carb.
Make sure its not over 4 psi.

I'd recommend buying the Weber Tech Manual by Bob Tomlinson
from CB performance. Can't beat it, especially since its only $10.

Has lots of good information about IDFs and how to rebuild
them tune & troubleshoot them.
I think it's better than the Weber Haynes manuals.

http://www.cbperformance.com/catalog.asp?ProductID=4

--- bill

Adjust your float levels per diagram. You tweek the two tabs accordingly until you get the desired clearances, and this is WITH the gasket installed.

If BOTH carbs overflow, it's more likely to be too much fuel pressure (2.5-3.5psi). There are inexpensive adjustable regulators available.

If only one overflows, then it's more likely to be dirt in the needle valve, or a worn needle valve, or a misadjusted float.

I seem to remember you saying you just rebuilt these carbs. Did you replace the needle valves? If you didn't adjust the floats, you certainly should. I can't remember the numbers off the top of my head, but there's one number for "float fully down", and another number for "float just kissing the needle valve". There's a ball on the end of the needle valve and it has to NOT be pressed in when measuring the "kissing" number. It's best to do this by holding the float plate vertical with the float hanging down. Angle it so the tab on the float arm is just barely touching the extended ball on the valve.

A misadjusted float not only causes overflow, but can also throw off the mixture if the fuel level is too high or too low.

Finally, really good fuel filters are critical to keeping carbs working properly. Very small dirt particles will clog the idle jets and cause no end of drivability problems.

The numbers in the chart, btw, are in mm.

I had the SAME thing after I rebuilt my webers, pulled the top off, adjusted the float actuator(aka metal tab) and it worked like a champ... the weber book says something like when the needle is engaged, the float should be paralell with the carb

I just rebuilt these and the kit came with a new needle valve. Only the right carb over flows, the left is fine.

you are the first person i've heard report actual success with Grose-Jets.

they don't work in 914.6's and they don't work in 356's from every other report.

i don't know that i've heard of them being used specifically in a 40 IDF so maybe that's the exception.

in /6 40IDTP13C's they exhibit very poor flow control and lead to overfull float bowls with the usual expected results.

i'm glad they're working for you. everybody else has put them in the category of a neat part that ought to work great - but doesn't ...