Float level advice, please.

[siteunseen]

Run both on rear tops. 

I've got some Grose valves I will send you thanks of our hero @240260280

I'm keeping the new ones, you can have the used ones.

 

[Captain Obvious]

46 minutes ago, siteunseen said:

Run both on rear tops. 

I've got some Grose valves I will send you thanks of our hero @240260280

Thanks for the generous offer, my friend! If I can't figure this out I'll take you up on that.

I've thought about running rear tops, but they're giving me the same problem. Level is higher, but not high enough. Arrrrrgh!!

[Duffman]

I was thinking the same thing; maybe having the short ear version of the fuel bowl lid on the front carb would help get the desired fuel level.  But, you are saying that won't make a difference, right?

[Captain Obvious]

If I get a chance, I'll put the rear lid (short ear) together and take a couple pics.

Both lids have complications. The short ear lid has the float pivot point closer to the underside of the lid. That means there is less float tilt available before the float hits the lid.

The long ear lid allows more float tilt before the float hits the lid, but there's another problem...Since the whole system was designed originally with short ears, the shape of the float was designed to never bump into the inside of the bowl. But if you go extreme tilting of the float (further than it was ever designed to tilt), it WILL contact the inside of the bowl.

The bottom line is... Too much tilt is a bad thing.

And as an anecdotal piece of info... If you look at the pics in the old FSM's you can see where they "expect" the fuel level to be on the float when there is enough pressure to close the valve and the relative tilt on the float. Note that the float is shown as pretty much no tilt. Float is "neutral" and from a design standpoint, I think that makes a lot of sense:

[Mark Maras]

 For what it's worth, the floats on my 71 never sat level when adjusted to the proper height. They always were up higher than the pic but they didn't hit the lid or the walls. I may have missed it and it's Obvious as hell but did you confirm the actual float dimensions are the same as the old ones?

[Captain Obvious]

I didn't Archimedes the new and old floats to actually measure the respective volumes, but yes... I took a bunch of mechanical measurements to verify that the new aftermarket floats are the very close in size and shape as the old OEM floats. And I also weighed them with a (non-NIST) scale and they all came out to 10g. And in addition to all that, I did check the wet float level with the old OEM float as well and it was about the same.

So the bottom line with all that is it appears that it's not the float that changed.

That brings me to either the fuel changed, or my aftermarket float valves are more sensitive and close sooner than the originals.

[Captain Obvious]

So here's some pics of a trial run with the 72 rear (short ear) lid.

First attempt. Float tab looks like this:

 

That float tab resulted in a fuel level and float tilt like this:

 

Bending the tab a couple times bought me to here:

 

Which resulted in a fuel level and float tilt like this:

I'm not quite hitting the lid yet, but I'm very close. And I'm still pretty far away from my target level. I don't think I've got the compliance left to bring it up to target without hitting the lid.

Edited June 9, 2021 by Captain Obvious
typo

[Namerow]

7 minutes ago, Captain Obvious said:

I'm not quite hitting the lid yet, but I'm very close. And I'm still pretty far away from my target level. I don't think I've got the compliance left to bring it up to target without hitting the lid.

Suggest you layer or sleeve the tab. 

[Captain Obvious]

5 minutes ago, Namerow said:

Suggest you layer or sleeve the tab. 

Hmmm... Thanks for the input, but I'm not really sure what you mean by that. Are you suggesting that I add material to the top side of the tab?

If so, that would only make matters worse. The problem is that the tab is already too high. I need it lower, not higher.

[Captain Obvious]

I think I understand the sentiment though... You're thinking that if there were something layered on the top of the tab, the float would sit more level, right?

It's a little counter-intuitive, but that wouldn't work. That layer would just close the valve sooner thereby lowering the level. Yes, the float would sit with less tilt, but the level would drop accordingly.

Edited June 9, 2021 by Captain Obvious
more typos - need new thumbs

[siteunseen]

Can you bend the whole bracket down anymore, the pin holder?

[240260280]

For quick and dirty float level setting, I just blow into the fuel passage and tilt the float until the air is blocked.  I then just adjust the float tab so that this stop point occurs when the float is perpendicular to the float tower. 

The only delta from in use is if my air flow is ~3psi. 

 

The nice thing about this process is that it is independent of tower type.... and this is the confusing part as a long tower will have less fuel in the bowl than a short tower.  72 Carbs are just too crazy for my brain to understand.  The design could be for dealing with acceleration/deceleration and float swing/fuel slosh but it could also be some weird way to deal with the problem of vapour lock and having less fuel to soak up the heat.... my head spins!    Remember those copper crush washers in the rear hub to cure noise?