Weber 40 IDA 3C Floats measure and adjust

M491Cabriolet · 12-14-2018, 05:34 PM

OK... I’ve read just about everything I could, but can’t understand the float adjustment. Carbs on the bench after rebuild. The problem is, I think the authors out there assume I have a clue, and I don’t.

So, with the carb sitting up, bowls dry and floats resting in the down position, the needle valve tab should be at 18mm from the gasket surface. I think I’ve understood that. Right?

But the next measurement, the measurement of the same surface to top of the float is nowhere near the 12.5-13mm I’ve read about. It’s maybe 5mm or less. And when lifting the float to its highest point, it’s like 23mm.

What am I not understanding? Can someone help me? Please assume I know little to nothing. Thanks!

juanbenae · juanbenae's Garage

do you have one of those measuring vial that screws to the float bowl? ive only adjusted floats with the units in the car so the vial readings were all I had to go on to get them shimmed correct.

what you are doing is way beyond my experience, but one of the measuring vials may allow you to check your work as you go??

Trackrash · Trackrash's Garage

Performance Oriented used to offer this procedure. Basically get it close then use the vile on the carb once it is running.

Adjusting the physical relationship of the various components of the float assembly is a little tedious without a jig but it can be done with a little patience. The important dimensions are:

The top of the float body should be 12.5mm to 13.0mm above the top surface of the throttle housing when the tab for the float needle is correctly positioned
The tab where the fuel needle contacts the float should be 18mm below the top surface of the throttle housing
This tab should also be perpendicular to the axis through the needle valve
This tab should be flat and without any divots on its contact surface
The tip of the float needle should be 18.5mm below the bottom surface of the top cover
The extra 0.5mm is to account for the thickness of the sealing gasket used between the top cover and the throttle body
This measurement should be performed with the top cover upside-down to simulate the needle valve in its closed position

Trackrash · Trackrash's Garage

Here is the dimension that is being referred to. IMO, just put the carb together and after running, use the vile.

Steve@Rennsport · 12-14-2018, 11:35 PM

I've done this both ways for many years and I've had the best successes using a pair of the threaded vials per carb and shimming the needle assemblies as needed.

Works perfectly every time.

M491Cabriolet · 12-15-2018, 02:50 AM

Is the measurement of the top of the float body at 12.5-13 mm measured when the float is lifted or sitting down in the bowl?

How does one actually make the adjustments to the float? What do I bend? I don’t get it!

I do not have a vial. Do they come with idiotproof instructions?

Thanks, all!

l_turn9 · l_turn9's Garage

Hello - I am a distributor for PMO and am including a image of the Float Tool we sell with the instructions written by PMO.

You'll probably need to enlarge the image to read the instructions. When I had Webers on my 911 I always set the float level using shims under the needle valve. I know there are lots of instructions out there and you must choose what works best for you. It's been a few years since I had to adjust them but I seem to recall the float adjust you are talking about is to be used during the rebuild to get the floats in "the ballpark" but you need the Float Level Gauge to adjust the fuel level precisely. Please remember just a little bit off the the fuel level can cause all kinds of trouble - from fires to flooding to a lean condition that at the extreme can burn pistons and valves.

I didn't look but I suspect Pelican Sells the Gauge Kits as well...

I'll be happy to sell you our Float Level Gauge Kit which comes with an assortment of shims. We also offer a separate package of Shims should you need them.

I hope this is helpful. Good Luck - youroil.net
LarryT

M491Cabriolet · 12-15-2018, 04:04 AM

Ahhhhh.... THANK YOU! I think I have finally understood. The float level adjustment has nothing to do with the floats, really. It has to do with raising or lowering the distance between the needle valve and the tab on the float, which actuates the valve (shutting off fuel flow at the appropriate time). This is good news. I feel like I can close up the carbs ad install them, then test with the vial you have. Thanks again.

l_turn9 · l_turn9's Garage

M491Cab, Happy to help. I know how frustrating it can be when working something as complex (IMO) as carbs and things just don't make sense.
LarryT

Trackrash · Trackrash's Garage

Yea, I'm not sure that the 12.5 - 13 measurement makes much sense. I guess if the tab that the needle and seat pushes against is level, then the top of the float should be 12.5-13 mm above the body. I've never bothered with any measurements with the carbs apart. The vile is the only way to get the floats set properly.

john walker's workshop · 12-15-2018, 03:56 PM

Vile vials! Only way to fly.

Gordo2 · Gordo2's Garage

Mid-way down this thread are photo's and process I used to set the float height on my PMO carbs:
Gordo's PMO Carb Tuning

Not sure if the Weber's float setting / setup is the same as PMO.

Either way, sounds like you got it figured out.

Good luck, Gordo

hienz · 12-15-2018, 07:29 PM

Quote:

Originally Posted by l_turn9

Hello - I am a distributor for PMO and am including a image of the Float Tool we sell with the instructions written by PMO.

You'll probably need to enlarge the image to read the instructions. When I had Webers on my 911 I always set the float level using shims under the needle valve. I know there are lots of instructions out there and you must choose what works best for you. It's been a few years since I had to adjust them but I seem to recall the float adjust you are talking about is to be used during the rebuild to get the floats in "the ballpark" but you need the Float Level Gauge to adjust the fuel level precisely. Please remember just a little bit off the the fuel level can cause all kinds of trouble - from fires to flooding to a lean condition that at the extreme can burn pistons and valves.

I didn't look but I suspect Pelican Sells the Gauge Kits as well...

I'll be happy to sell you our Float Level Gauge Kit which comes with an assortment of shims. We also offer a separate package of Shims should you need them.

I hope this is helpful. Good Luck - youroil.net
LarryT

How much for the gauge kit?

l_turn9 · l_turn9's Garage

$60 with Free Shipping for the rest of Dec. Please use Promo Code Pelican

Sincerely
Larry
youroil.net

ed mayo · 12-16-2018, 07:52 AM

The 18mm to float tab while at the same time the top of the float should be at the 12.5/13mm float height is a BASIC adjustment to ensure you will then be in the right range to achieve proper float level height using the float level gauge and shims under the needle seat. In other words you start with a basic then follow up with the fine adjustment using the level gauge on a running engine.

Jack Stands · Jack Stands's Garage

The site glass on the PMOs were a nice improvement over the Weber design.