Float Needle seat

[trappnman]

Slowly breaking in the new rebuilt Combat, and so far so good- engine seems tight and strong, 1st kick bike, more than pleased.

With one exception- the carbs. After trying everything- heating up float bowl and adjusting float seat, new gaskets, new needles, lapping the needle seat It became apparent I needed a new seat. I got Stay up floats at same time.

I understand setting float level and thats not my concern.

but I've exhausted my searching for anything talking about replacing seats, and how deep they need to be installed. My best guess is flush with the carb body-

My concern is not being the right depth to fully seat needle. Or am I over thinking it, just set flush, and adjust tang as needed?
Any advise appreciated

 

[Tornado]

Can you determine current seat position in bowls and just get new ones close? They are adjustable to set original float heights, so there is no correct position in that sense.

 

[o0norton0o]

I never used the modern floats with the adjusable tang, but for the normal floats the seat is just about 1/16" above flush.

Once it's all assembled you gently push down on the tang of the float (not the top of the needle) and the body of the float should NOT be above the rim of the bowl or it might not seat the needle before it contacts the underside of the carb body...

 

[trappnman]

thanks

 

[trappnman]

I went to the source (Amal) and got this reply from a very nice man named Oliver:

You need to make sure the float needle seat is screwed in right to the end of the thread and flushed. Any less will allow fuel to travel up the thread and leak.

The only components that you need to adjust is the float. The needle and seat are adjusted by the fuel level, if properly installed.

 

[Fast Eddie]

Trappnman,

What are the symptoms of the problem that you have (that leads you to suspect the seat is at fault) ?

 

[L.A.B.]

You need to make sure the float needle seat is screwed in right to the end of the thread and flushed.

Screwed? The Mk1 Concentric float needle seating isn't screwed in.
And no, it shouldn't be flushed.

Shop our MK1 Float Needle Seat .125 | 622/121 | AMAL Carburetters

MK1 Float Needle Seat .125"

amalcarb.co.uk

Note that the original seating hole diameter was 0.100".

 

[trappnman]

yes, those are the replacements I have.

I would assume "screwed", simply means pushed in>

but why would you say not flush- when Amal said flush, and Andover Norton said to see the Amal email to me. So both seem to agree flush, bottomed out.

Why do you say not flush? If you have info contrary to what I received, I'd like to hear it.

What are the symptoms of the problem that you have (that leads you to suspect the seat is at fault) ?

immediate overflow with nothing working- new needle, adjusted float, new gasket, tried lapping seat. I've got the new seats, got the new floats- just want to make sure of the "seating" of the seat before I install.

to boil down the advice given to me, is to set the needle seat so that it bottoms out on the threads- which, it seems, would be flush. I'll measure before I start

Again- I'm not stating this as fact, just what I've been told from the 2 companies.

 

[L.A.B.]

Here are two new float bowls off the spares shelf. I hope you can see that neither seating is flush, only the bottom of the champher is.


Amal did give a depth dimension in their tech section at one time but it doesn't seem to be there now. Measuring the two that I have, the distance from the bottom of the seating to the gasket face is 0.565".

 

[Fast Eddie]

“Immediate overflow” sounds more like a stuck float preventing the needle from sealing on the seat in the housing.

I can’t really imagine what kind of damage there would need to be on the seat to allow “immediate overflow” if the needle is seated upon it, but I would suggest the damage would be clearly visible.

And it’s such a simple thing, it’s hard to see what could actually go wrong with it in order for it to be the cause if your issue IMO.

Something holding the needle off the seat, or a damaged needle tip, thats my guess.

 

[Tornado]

“Immediate overflow” sounds more like a stuck float preventing the needle from sealing on the seat in the housing.

I can’t really imagine what kind of damage there would need to be on the seat to allow “immediate flooding” if the needle is seated upon it, but I would suggest the damage would be clearly visible. And it’s such a simple thing, it’s hard to see how it could be the cause if your issue IMO.

Something holding the needle off the seat, or a damaged needle tip, thats my guess.

Perhaps the gasket impinging on the float hinge pin? Believe Greg Marsh has shown how he trims the gasket near the hinge area.

 

[jan nelder]

I had a sliver of plastic (from somewhere) which was difficult to see, and stopped proper seating, so it flooded pretty fast!

 

[o0norton0o]

What seems obvious to me is if the seat is flush instead of slightly above flush, as shown in LAB's photo's, then the float would have to rise higher to send the needle down further to seal......SO, if the float is hitting the underside of the carb body before it seats the needle then it can't shut off the flow of fuel....... Immediate overflow is the result...

and you can bend the tang on the new style floats or drift the needle seat up higher in the bowl with the old plastic floats...

 

[trappnman]

trust me when I say the seat was bad- they DO wear out. I didn't miss anything obvious ie stuck float, etc

Thanks L.A.B.....

when the seat is fully flush to the bottom, then it sits as L.A.B. shows above the bowl body. I think that was what was meant about flush- not at the top, the bottom.

New seats in w/o any problem, new floats- problem solved.

thanks again

 

[trappnman]

L.A.B.- you mentioned the size as .100 OEM, and the replacement as .125. The replacements don't have the hole in the side of the seat- I'm guessing maybe reason for being larger?

 

[o0norton0o]

The needle seats came in 2 sizes. I have early amals which had the smaller needle seats, I've replaced them with the larger ones and since the needle actually meters the flow, both of them seem to work the same on my amals.... Possibly the larger seat was to make sure the larger amal bowls didn't run out of fuel at wide open throttle..... but to the best of my knowledge they both work.

 

[L.A.B.]

L.A.B.- you mentioned the size as .100 OEM, and the replacement as .125. The replacements don't have the hole in the side of the seat- I'm guessing maybe reason for being larger?

I think the hole in the side of the seat you mention is a modification.

See diagram in the link (11th page).

https://static1.squarespace.com/static/547e5122e4b0193d67f28396/t/5854ddf6725e25b3b4c06d52/1481956877861/Amal+MK2+Carb+Manual.pdf

 

[L.A.B.]

The needle seats came in 2 sizes.

There were at least six sizes originally, 0.100" being the standard size. See "Float Bowls" in the link above.

However AN at least, now appear to be selling the 0.125" seat float bowls as standard.

Andover Norton - FLOAT CHAMBER (.125

FLOAT CHAMBER (.125

andover-norton.co.uk

The original drain plug float bowl is 622/055(S).
https://amalcarb.co.uk/mk-i-concent...loat-chamber-bowl-0-1in-standrad-seating.html

According to the 850 Mk3 parts book the Mk3 float bowls (622/056) had the 0.125" seat as standard.

 

[trappnman]

L.A.B. your link to the amal carb was very informative, definitely bookmarked for future reference.

Yes, there is a hole in carb body as well. I bought bike in early 90s and was 2nd owner, and the previous owner didn't seem like the type to do this mod. Do you think this was done at factory, maybe for Combat engines?

 

[L.A.B.]

Do you think this was done at factory, maybe for Combat engines?

No, I don't think so.