Carb 'Stay-up' Float Kit

[Edin Dundee]

I now have my carbs in pieces on the bench, trying to get to the bottom of an erratic idle. I've replaced the poppet valve discs with what looks like (to me) a very expensive pair of plain brass discs. I've checked out the float needle valves, look OK but there's a bit of lateral movement on the floats, so I think I'll replace them. I need new chamber gaskets.
Has anyone used these new style floats here:

http://www.sucarb.co.uk/productDetail.aspx?id=33997

I'm a bit worried about the 'adjustable' bit.

[Henk]

The adjustability doesn't seem new to me, looks like the older floats.
Early ones have a metal lever arm, like here:


Later ones are all plastic:


My best guess is that the 'unsinkable' theory is new.

[Edin Dundee]

Thanks.
What should the gap be in your diagram for HS4s on a standard 1850?

[VanIsleSprint]

The SU manual says:
For the HS type with an early type nylon float and steel needle, the gap between the lever and the face should be between
0.125"and 0.187"
For the float chamber and delrin needle (spring loaded) and new geometry float and lid, the gap should be between 0.125"
and 0.187" with the float arm resting on the needle plunger but not depressing it.
For the float chamber with the delrin needle and the later all nylon float, the gap should be between 0.062" and 0.187"
with the float arm resting on the needle plunger but not depressing it. This type is not adjustable.
The last statement is not quite true because it is possible to adjust the gap by using different thickness copper or fabric
washers under the needle and seat valve.

[soe8m]

Away with all those manuals. It cannot be done by the book. Never never ever. Told it many times before here but now with pictures why not.

If you do it by the book what you just have thrown away, both carbs have a very different floatlevel in the jet. That is what it is all about. The fuel is sucked out of the jet and that level is importand. The fuel must be about 6-8mm under the top of the brigde what's in the carb. Not the top of the jet.

You can measure it by pulling the choke till the top of the jet is 6-8mm lower than the bridge and the fuel level must be flush. It's a game of having the floats adjusted a few times before it's all ok. When the level is finaly set you can decide the floatchamber is ok or not and than change the floatchamber and set level again.

On drawing one you can see how the engine is hanging in our cars with the carbs attached. The floats nicely adjusted by the book and the front carb's just not flooding and the rear much too low. The rear will give a lean mixture. It can be adjusted at idle with the jet adjuster to have at idle a decent mixture but at driving revs the mixture does look like nothing.

When adjusting NOT BY THE BOOK AND THE ONLY WAY TO ADJUST, the front fuel level in the jet, the level can become too low in the floatchamber and then you have to change the floatchamber. This is noticable by driving at speed there's not enough fuel supply.

There are different types you can fit and all have the same connection but the offset is different. You can have after changing the fuel level in the jet ok and enough in the floatchamber. Or the other way, the level in the rear jet cannot get high enough without seeping fuel trough the housing and cover. You have to change floatchamber also.

The different types are used on every vehicles with SU. Maybe your spare set has the right floatchambers to use.

Jeroen

carb1.jpg (18.14 KiB) Viewed 1832 times

carb2.jpg (14.73 KiB) Viewed 1832 times

[Jon Tilson]

With the supposed non adjustable plastic floats I have never needed to do any extra adjusting of float level as Jeroen describes.
You can clearly see the fuel level by looking down the jet and also you can tell the mixture is right at idle by tuning each carb individually at about 1000
rpm by the piston lifting method.

Jeroen's theory is of course absolutely correct, but in practice if the carbs are the ones the car came with and the floats are not sinking, its all going
to just work. Of course the same principal applies with strombergs, but on these you get adjustment by bendy tabs and getting them set right is a bit of a fiddle.

Jonners

[soe8m]

The idle mixture set up does not work this way. The rear has to suck harder for the same mixture. You are tend to have the rear jet lower to have the same idle mixture as the front. At idle all is ok but at different revs and pull the mixture is not he same front and rear anymore.

The stromberg and SU HIF can be set up by the book. They have the jet centrated in the floatchamber. When you have a glass of beer and hold it at any angle, the exact middle will alway's be at the same height, so no influence of hanging engines or angled carbs. If all parts are original and fitted the way BL intended it does not mean it's ok.

Jeroen