Weber float problem

[Lyndon302]

My 68 911. Setting the float levels. All good until I get to drivers side rear. Using the external PMO gauge it almost empties. Then over flows. I have changed the float and the float valve. Still the same issue. What am I missing ??? I can get it to settle. A bit of a rev etc and I can make it misbehave at an idle and my engine runs ruff.
Side note my idle mixtures on all six seem to Bugger all 😦
Lyndon

[john walker's workshop]

Float valve quality is lacking. Try another one.

[Lyndon302]

I have put new float valves in the rebuild.
So I put an old one back in after this issue.. Your saying both arnt any good. ???
If so I have 3 other old ones I can try.
Lyndon

[john walker's workshop]

The last set I did were for my own car and I had the same problem with the new valves from the kit.

[Trackrash]

Yeah, something about the needle valve.

I would use a piece of welding rod to poke down the vent tube and wiggle the float when it is idling to see if you can get it to seat with the motor idling.

With the top of the carb off blow into the fuel inlet and see if the needle will seat when gently pushing on it.

It could be that there is a problem with the part of the float where the needle rests. It is bent out of shape or there is a burr there causing the needle to not seat.

Also, make sure the float is installed correctly, not upside down and that it can move freely throughout it's range and not hanging up.

[Lyndon302]

I have changed the float already. All good advice. I will give a try again tomorrow.
Lyndon

[SCadaddle]

I had this issue on a Honda ATV carb a few years ago that drove me nuts. Finally took it to a guy that rebuilds them for a living and he diagnosed a "rough spot" in the float valve seat. But it's how he did it that (I paid him for) that I retained.....

1) hook up a fuel line to the carb from a container of fuel---think IV bag here.
2) With the top off of the carb so that you can see the float and such, turn the carb **upside down**. This will make the float fall by gravity and **hopefully** the float valve needle will close like it is supposed to do. When you see it leaking, take a small tool such as a wooden dowel with a small piece of scotchbright and polish the float valve seat and try again.

[john walker's workshop]

Hard to do that with a weber needle and seat unit.

[juanbenae]

hasn't Sir Paul done some testing on currently supplied float needle and seat units suggesting that their failure rate was as high as 4 in 10? maybe he will chime in or someone will find and link at least one of a couple threads ive read on his experience testing them..

[Lyndon302]

I have spoken to Paul. He is a most helpful bloke. I'm currently peening my old float ( I have changed it out with a new one. No different) also cleaning all my old valves and will rotate them thru till its fixed
Lyndon

[Jack Stands]

Are Grose Jet float valves still an option?

[TimT]

Are Grose Jet float valves still an option?

I've been sitting here trying to remember that name..

They were a good cure... little ball valves almost

[Lyndon302]

All fixed. Float Peen. Polish and found an valve that works fine.
Now it won't return to idle like it should.2000 rpm then settles down.. Its not the throttle jamming.
Lyndon

[1QuickS]

Double check that dizzy advances and returns to initial setting easily. Remove dizzy cap and manually actuate advance of rotor to see if it moves freely. Check idle timing while you are at it. Failure to return to idle, if the above are satisfied would then be rich idle mixture. Check fuel delivery pressure is 3.5 plus/minus 0.5 psi with engine running. Check to see that idle stop screws are 3/4 to 1 turn open from throttles closed and idle mixture screws are 1 3/4 turn open from closed as a starting point. Also (this is important to be sure of) early (1968 and earlier Webers) did not use o-rings on the idle jet carrier screws and later bodies did use an o-ring. If you use the "later" idle jet carriers in earlier bodies then the idle fuel jets WILL NOT SEAT and will allow excess fuel to be delivered to idle mixture screws causing a rich idle mixture which in turn will result in slow to return to idle speed and/or high air flow at idle. If you do not have a STE air flow synchrometer then get one. It will indicate an air flow at idle that will be around 5.5 to 6.0 thereby indicating throttle valves are properly set to idling position and you should then be able to achieve Lean Best idle mixture.

Adjusting floats to OEM geometry per the drawing I sent to you will result in a float needle valve shim thickness of around 0.070 inch plus/minus 0.010 inch. Peening the back side of the tab where the float needle valve rests is important to re-establish a virgin interface with the needle valve.

Many details to attend to but none are difficult, just exacting.

Regarding float needle valve testing: I wet pressure-checked 200 needle valves for PMO and saw 8% failure and the next batch of 200 I saw 1% failure so Richard & I agreed to call them OK for now. He is considering manufacturing needle valves of my design that utilize Viton-tipped needles (as sourced from Holley carbs) and are infinitely adjustable like setting valves on your engine.

[Lyndon302]

All sorted. Pending a road test.
Float fixed as previously mentioned.
This car has been sitting so its all an unknown to me.
Tuning what did to get a good idle and return to idle.
Idle screws in and also air by pass screws.
By ear I adjust the air by pass screws out for a smooth idle while letting the idle screws out to lower the idle. Did this till the air by pass no longer increased idle while letting the idle screw out. Then the idle screw in so its just opening the butterfly. Then air by pass in till it runs rough and back off a tad.
Then checked the readings. All at 5 with a nice idle. 😛
Bring the revs up to 10 ( just above idle ) on the gauge and balance the carbs via the linkage to to be even.
I got high readings at idle because the butterfly where to open. With these closed to 5 and the air by pass open up it runs like a treat.
Mixtures out till no backfiring
A road test will reveal all. Next week hopefully I will have rego to drive it.
Lyndon

[rgofast]

If your having float problems make sure you have air free fuel supply at the correct constant pressure. We completely overhauled our fuel delivery system, and installed a regulator with a return line. This eliminated the intermittent overflow problems

[l_turn9]

Also be aware that the linkage adjustments are very sensitive. Being slightly "off" can cause erratic behavior. Make sure you follow the Carb Synch/Tuning carefully and in the correct order.

Good luck -