Leaky float valves, 80 Plus.

[KiwiJohn]

Leaky float valves.

I have my 80 Plus looking really good and it even runs but fouls the plugs in just a few minutes due to excessive fuel, apparently.

I have checked carbs for correct slides and needles, even had the slides sleeved and the float needles replaced but there is just no way I can stop those floats from leaking.  When the engine is stopped fuel continues to rise in the float bowl and to run out the main jet aperture.

The does not seem to be any way I can examine the valve seats.

Is there any way I can lap the needle valves into the seats?

[graeme]

John,
Have you checked that the floats are actually floating? It takes only the tiniest hole to slowly let fuel enter the float and cause rough running.

[KiwiJohn]

Thanks Graeme, I did check for leaks but I will go back and be a bit more thorough.

[trevorp]

it may sound silly but if the fuel comes in from the bottom of float u need a diiferent arrangment for needle and seat than if fuels comes from top of float bowl

[KiwiJohn]

Trevorp......   Hmmmmm, I am not sure I understand you, are you telling me there are different ways to assemble these carbs?

[trevorp]

i have noticed that some douglas are fitted with amal carbs and the fuel inlet is mounted on the bottom of the float bowl most have the fuel line on top of the float bowl if your fuel inlet is on the top of the float bowl then your needles and seats are leaking but the carbies that have the inlet on the bottom of the float bowl have a completly different sytem and the float pulls a needle up from the bottom
i will try and find some diagrams
but if your fuel inlets are on the top of the float bowl then u have normal needle and seat problems which can be fixed by lapping needle with a bit of 1200 wet and dry sandpaper just twirl in fingers and check the seats

another trick i have learnt is if u buy a union that goes on the bottom of the amal carby that holds the 2 bodies together that has an outlet all u have to do is put a bit of clear tube on it and hold it against float bowl this will show u the fuel height in the bowl if it goes above the height of the top of the float bowl then needles and seat are leaking if not mark the height on the tube and check the other side is the same as float level is critical on amal carbies
im sorry i dont have the info for float height but this may point in in the right direction
if not ill try and help all i can
Trevor

[KiwiJohn]

Trevor

Mine are the ones with fuel entry at the bottom, there is a long needle with a conical piece on the bottom end.  As the float rises it pulls this cone into its seat.

I have considered cutting a screw driver slot in the bottom of the cone and try to lap it with valve grinding paste or something.  The only thing holding me back is that I might muck it up and destroy them.

John

[Doug]

John,

About the only worry with lapping is ending up with a conical seat that is too wide, as these will be prone to leak.  Instead of providing a better seal, it makes matters worse as the alignment of the needle needs to be that much more perfect else the cone of the needle and the cone of the seat are held slightly apart.  Nor does the wider seat seem to impart any self alignment properties.  It just leaks.  The ideal would be a knife edge, the needle could be at quite an angle and still close up the hole, but this is not practical either.  So a narrow seat is best.  

If you have replaced the needles, then there are no worries about a groove in the needle to rectify.  Unless you over do the lapping!

-Doug

[trevorp]

good point doug.
 i would only lap the needle as this will change the point of contact on the seat.
 and may help if your carbies ar premonoblock 276 bottom feed needle kits are available and floats are available from hitchcockmotorcycles.com part number is AM/14/015 $15.50 pounds for float and needle kit may even pay to drop them a line and ask advice on the seat or a quick fix

[trevorp]

also the icypole stick method of adjusting the slides is a great trick
just put stick under each slide and turn throttle and make sure both move at exactly the right time makes for better takeoff just above idle if the slides are in unison

[alwyn]

also the icypole stick method of adjusting the slides is a great trick
just put stick under each slide and turn throttle and make sure both move at exactly the right time makes for better takeoff just above idle if the slides are in unison

Hi "trevorp"
Sounds interesting - I thought an icypole was an iced confectionery - but if it's related to synchronising the throttle slides on both carbies could you elucidate for the unitiated please. :
Alwyn
Site Mod.

[KiwiJohn]

Right, thanks very much.  Hitchocks' website gave me information I didnt previously have so as a first step I will be taking a wee dram and my big spanner and tightening the nuts at the bottom of the carbs.  It mentions that these must be tight to prevent leaking and over rich running.  Maybe, just maybe, if I can tighten them enough without breaking the carb body I will cure enough of the over rich condition to make the float needle leak insignificant.

I had not thought of the needle needing a knife edge to mate against, I was assuming the orifice in the body of the float chamber was a matching cone ('anti-cone'?)

[Doug]

John,

The valve seat is indeed a matching cone; just a (hopefully) narrow portion of one.    

A knife edge would be idea, but impractical for various reasons.  Foremost any imperfections in the finish of the needle or the seat would be a short path for the fuel to leak by.  

-Doug

[trevorp]

icy pole sticks just fit in the bellmouths under the throttle cutaway and therefore under the slide u just put them under each slide and slowly rotate the twist grip and u can visually see if the sticks move in unison or if one moves first
as the slide raises the sticks droop down and u will be suprised how easy it is and how well it works
and the best bit is u get to eat a couple of ice creams as well
just adjust cable to get working perfectly

[KiwiJohn]

Please see my new topic regarding flooding post war carbs,  it appears the float valves were not really to blame.  

New topic HERE
Added link 27/05/2005
Alwyn
Site Mod