Wrestling with the T10TT carb...

I can't pretend to know all the answers but in regard to different floats, the new Amal float needle in a new 276 carb has two grooves. One for new plastic floats, and one for original. So the needle might need changing at the same time if such a float is available.

The books I have suggest lapping in the float needle with metal polish. 2 drips a second does sound like it's not seating.

Someone might correct me but I think the holes are to stop fuel running down the inlet tube into the cylinder if the fuel level does become too high. So they are doing their job.  They are too small for pilot air.

Can you measure the level? If it is too high or the float needle leaks it will rise slowly until it is above the holes in which case they must drip. Does it leak when running? With metal to metal seal, the tank tap needs to be shut when parked up for any length of time. It might be OK when running.

They are not like the viton seals on new carbs. I accidentally left the fuel tap open on my Dommie for over a week and it did not drip, but that has viton tipped float needles.

I agree with David.  I have several older type carbs and worn float needle seatings  can sometimes be helped with a little  metal polish /brasso etc but  a replacement  seat is a much better bet. These carbs are a bit of a fire hazzard  at the best of times  so well worth getting it properly sorted.

... T-cut to lap in a leaking brass fuel tap (the taper type) and it worked well. I'd guess the same would be true of the float needle and seat. I think it may be slightly more abeasive than brasso etc.

The 15 degree inclination to keep it level can be varied by axial location on the carb.  Make sure you position the float chamber  on the carb to give you the lowest level to stop the leak then work it forward till it leaks again. If at the lowest point it still leaks refer to above …

common issue float valve leak.  Are you top feed or bottom feed?  Three holes around the base of mixing chamber are for air feed to emulsify the mixture as it heads up the main choke. Remember the machine  is riding at a different posture when you ride it.  You may be trying to overcome an issue that isn’t when your on the move.

 Mine is bottom feed, lapped with collar Chuck mounted on oscillating valve seating tool connected to 8BA drilled and threaded into bell end of the needle. TCut, Brasso, Silvio and rouge …. Improved but still the fire hazard Robert mentioned.  Now I’m experimenting with a lower clip groove to get some control  the lapping may have it seated a bit deep…

Have you checked out your spam ? Package left two weeks ago…

Jon

I had to cut a new  groove for the float clip  to adjust the fuel level. All done by hand tools and a mini hacksaw, but it worked.  I had the opposite problem  ,a low fuel level  due to incorect parts.

hi

been caught out with this one on the 15TT on my Inter. Agree with Jonathan, turn float bowl to lowest point....remember, carb is inclined. If no joy, then i would suspect float level.

Dave

The first part of recap correct but that closed position shuts the fuel off but at a level that allows the fuel to leak out of the mixing chamber.  By rotating the bowl around the fixing point under the mixing chamber that shut off point changes… don’t forget the carb is angled up (downdraught) and the connection flange set at 15 degrees.  What ever that closed point is it moves as you rotate the connection. 

J

PS: mail received, package posted on 18th 

...and it follows from what Jonathan says that since you have it on the bench you can now measure the static fuel level accurately, and see exactly how far it is above the holes. Then you could turn a new groove on the needle to change the clip height so it stays just below the holes.

My own personal experience and that of others with Inters I know is that when you tickle the carb you end up with a continuous dripping. When you start the machine the the dripping stops and does not resume until the next time you tickle the carb.

I agree this is not ideal but it does seem to be pretty commonplace as far as I can ascertain and is generally regarded as just another characteristic of TT carbs. A bit like the absence of a tick over.

The amount of fuel head  above the carb will  give a varying amount of leakage ,especially if the needle seating is a bit marginal , thats why a new seating and needle  is a good move. If after getting that right  it still drips its also possible to have a missmatch  of parts  at the bottom of the carb.I had this on a Rudge ulster which needed an extra needle groove.  A Ducati with a Dellorto SSI  (TT type)  gave me years of  trouble till I fitted a new old stock  remote  racing float chamber,which of course had a new seating. Looked pretty trick too !!.

As I understand it, the correct float level is when the fuel is just below the lowest hole so it does not leak.  If you leave it long enough without the engine running, the level will creep up anyway, and will leak.  But if you open the fuel tap and let the chamber fill by itself, it should not leak immediately.  It should then start to drip if you push the tickler down for a moment.  If you hold the tickler down, the level will rise above the small holes and it will carrying on leaking fuel until the fuel used by the running engine lowers it back again.  It should of course not leak when running.  When mine was giving starting problems (now sorted I believe), I put a piece of rag under the carb to collect the drips while fighting the kick start, and turned off the fuel tap if it was leaking.  Then try to remember to turn it back on after it finally got going!

Mine leaked from the banjo - which was also confusing.  The bore hole in the banjo was eccentric (badly made) and one edge is a bit narrow.  Eventually it's been sorted with Wellseal on the banjo flanges.

If the float cuts off the fuel at a level above the holes, it will of course carry on leaking all the time.

I only use the tickler now to check that the chamber is full.

Sorry I don't have it apart and it should be out in the sunshine tomorrow. And Amal (Burlen) can't help as they don't sell float chambers nowadays. If you buy a new TT carb you must buy a separate "matchbox" float chamber to go with it.

Is there a way you can rig up a polyethylene tube alongside it to compare the fuel level (with the hole blocked) with the height of the holes? 

If it is now leaking from the front (lowest) hole, you could block that one and see if it comes from the others which are higher. If it doesn't leak from them, you will know to within 1/8" what the level is.  

..on the outside of the float chamber with a pencil; when you are assembled you will see the level your fuel will sit at, relative to the mixing chamber...

 The lapping should deal with the sealing but make sure the float is free and the needle goes up into the top guide cleanly on the lid.  

You are right on point 1-5 and 7.  Point 6, Leaking from factory was standard for most TT Carbs.

Cheers

J

Its hard to realise that even by the 1950's modern synthetic seals were still so rare that nobody expected fluids not to leak. Remember car parks a few decades ago? They always had black marks from the oil leaking from crankcase and back axles.

Hope you enjoy riding it!

None of my  old TT type  Side float carbs leak when not running .  You have to get the fuel level below the bleed holes  or the motor will run horribly rich  and foul the plugs, wash the oil off the bore  and contaminate the engine oil. Could be you have the wrong needle , I would cut an extra clip slot . What is there to lose?.

Some float bowls are top feed ,some bottom, and there are  different carb bottom fittings and needles ,so its very likely you have some rogue parts  in the mix. A close study of the Amal literature  might throw some light. Its the main reason i switched to a remote float  which gave me unlimited scope for tinkering with levels. One bike had to be leaned to the right at traffic stops to keep running  , OK till you needed to put it in gear !!. If you carry on as you are you are going to need some fire extinguisher brackets on the front forks and some flame proof undies. 

A distant memory tells me that the fuel level should be  1 5/16"  below the top of the chamber body.  So it will look a long way down.

My needle clip is 3/4" from the top of the needle. The top of the needle is about 1/8" above the top edge of the float chamber body when float is at the bottom and it rises about 1/4".  Side view shows relative heights. It is not practicable to remove the float without taking the tank off.  21/32 is near enough 20/32 = 5/8" so your clip is a tiny bit higher than mine. So float needle is lower (more open) at a given float height so your fuel will be 1/8" higher. If the float does not cut off fuel even with a higher needle (bigger distance from top to clip) then some parts must be mixed up or float leaking maybe?

Hi David,  It looks like your float chamber could do with a bit more angle to get things vertical .

Maybe Robert...but it's dark, cramped and uncomfortable in the garage and I doubt if the camera was level! I'm not messing about with a carb that works perfectly!

Those tilted float chambers are allegedly hard to find. And I am fairly sure they came in several levels relative to the banjo. Have you lifted the needle by moving the clip down so it shuts sooner?

Also  and this might be clutching at straws...the top of the needle must enter a guide hole in the cap. If yours does not start off in the hole  maybe the cap is holding it down? Have you checked with the cap left off? It's only needed when running to prevent splashing. That would however cause major flooding.

Thought so...!

The needle with the long notch is what you get from Burlen. The other is what was fitted.

Clip is a replacement as the brass one had lost its shape and tension.

Not getting posted. Big files. 
 

The theory has not worked out.  The 15 is usually on the underside of the transfer port. There were 12 degrees also according to one of our team.

Any thoughts on lowering the connection to the carb with a small spacer?
Maybe the depression in the mixing chamber and fuel flow keeps the holes clear of fuel when running So it’s only dripping until it starts? 
I use a BMW to clear my head!!
Jon

Following this thread of issues sounds exactly like the problems I had when getting my Plunger Inter/Manx back on the road 10 + years ago. The engine is a ‘38 and has an alloy head with bronze skull and the carb of the same vintage. I too had had a 15 degree float chamber  and what ever I did with the float chamber position, float level, replacing the float needle, lapping in the needle, made no difference, petrol still came out of the small overflow hole. 
Luckily I had a another Amal float chamber that I could modify to work remotely. I was able to get this high enough to stop the petrol dribbling out and get the bike to start and run. However all was still not good as I later learnt I had slide with the wrong cutaway, more designed for full throttle running as the motor would die when slowing down and not pick up smoothly.

in the end I put all down to  the carb being so old it was probably past it’s best, I spent probably 3 or 4 months messing about and desperately wanted to get the bike on the road and ended up fitting a 930 Amal Concentric, problem solved, she starts easy, pulls like a train and ticks over when you stop... what’s not to like... a bike is to be ridden after all

.....was a Monobloc with an Atlas manifold bored to match. This gets the carb in the same relationship to the head and tank. Also enables use of a tidy air filter.