Author Topic: 1930 S6 Carb  (Read 7356 times)

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Offline Michael Scott

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1930 S6 Carb
« on: 12 Mar 2009 at 11:27 »
Dear All
I considered extending the recent topic on the T6 carb but my problem is in the detail.
I have a 5/116/S which was refurbished my Martin Bratby.
I have found that the float needle is too long (it jammed between the bottom and the top.)and on his advice shortened the bottom so that at least I have petrol in the carb.  The tickler does not reach the float and on a rolling road fuel starvation seemed likely.
I took the clip off the float needle thus raising the float level and got more sustained running.  I then took a similar amount of the needle shoulder with a lathe and that gave much better running.  I have not rechecked whether the tickler works but I doubt it.
The question is how do I know when I have machined enough off the needle?
Are there alternative needles?
The float has concave ends.
Regards
Michael

Offline Doug

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Re: 1930 S6 Carb
« Reply #1 on: 13 Mar 2009 at 02:09 »
Michael,

I rummaged through my S6 bits and came up with two floats and needles. One float has a concave bottom and convex top. The other has a convex top and bottom. Both have needles of similar dimensions. The distance from the top of the groove to the tip of the one needle is 1.036" and the other 1.050". Overall lengths are 2.910" and 2.860" respectively.

However the fact your float has a concave top really throws the above dimensions right out of consideration.

-Doug

Offline Michael Scott

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Re: 1930 S6 Carb
« Reply #2 on: 13 Mar 2009 at 11:14 »
Doug
Thanks for that.
For clarity my float bulges out at each end.
Both Martin and Surrey Cycles insist that the only needle length is 2.85 and Martin has kindly sent me a new one. That length jams top and bottom in my float chamber.

I machined the length to 2.755 and the groove to 1.070. The bike runs with that but not well. I could go to your 1.050 and see what happens.  Probably at the weekend.

However the mystery remains as to why my float chamber is too small.  It looks ok and right and fooled Martin.

I would like to have the correct parts rather than my machined parts if possible
Regards
Michael

Offline Doug

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Re: 1930 S6 Carb
« Reply #3 on: 13 Mar 2009 at 11:30 »
Michael,

They might have been trying to use standard upright 5/ Amal components. Some of the components interchange and some do not. For example the jet block needle looks the same, but it is shorter than the needle used in the upright 5/.

-Doug

Offline Michael Scott

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Re: 1930 S6 Carb
« Reply #4 on: 10 Apr 2009 at 10:03 »
Dear all
Just to round off this topic.
It seems that I have the wrong diameter float chamber but no one can give me details so I will hunt around the jumblies.
After shortening the needle I had I machined the shoulder up by 10 thou increments until the carb continuously flooded then added a thin washer (don,t ask, I didn,t measure it!)
That got me rough running which I and friends thought was due to the mag but a quick trip the refurbisher showed that the mag was giving nice blue sparks.  While having a nice cup of tea in the sun the refurbisher told of problems he had heard of with S6's with sealing the intake flanges.
Sure enough a heave on the spanner in several areas had two cylinder firing and twiddling with carb bells and whistles has a steady beat.
The first ride up the village was successfully accomplished; general euphoria all round.
I will probably take the timing cover off and use thicker and softer gasket material one rainy day after I have shaken down and solved some other issues.
Many thanks one and all.  The moral of this and other hunts for technical solutions is join the club(s) and ensure a wide circle of friends and acqaintences.  Plus do not be afraid to ask silly questions.
Michael

Offline eddie

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Re: 1930 S6 Carb
« Reply #5 on: 10 Apr 2009 at 10:37 »
Michael,
             Be careful when refitting the timing cover - the studs/through bolts clamp several components, i.e. the primary chaincase, the crankcase halves, the timing gear outrigger plate and the timing cover. Make sure that you retighten them in the correct order - with all other nuts loose, tighten from the LH side to clamp the crankcase halves and chaincase, then tighten the nuts that hold the outrigger plate, then finally fit and tighten the timing cover. Any other sequence will leave the internals loose whilst from the outside all bolts appear to be tight. Before fitting the timing cover, put it in place without gaskets and check for gaps between it and the crankcase and between it and the inlet ports on the barrels - then shim up accordingly before final assembly with gaskets. The use of shims and thin gaskets is preferable to thick gaskets as tightening on thick gaskets can result in distorted and eventually cracked timing covers - a common problem on S6's.
       Going back to the carburettor - shortening the needle may not give you the correct mixture - not only is the needle shorter on the vertically mounted carb but the jet assembly is also shorter, thus requiring the taper to start higher up the needle. Also the fuel level is extra critical with this setup - especially as any flooding dumps neat petrol straight on to the hot exhaust pipe!
                                  Regards,
                                                Eddie.

Offline Doug

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Re: 1930 S6 Carb
« Reply #6 on: 10 Apr 2009 at 12:05 »
Michael,

I wrote to AMAL in the mid-eighties, and they supplied me with a copy of the drawing for the shorter needle for the jet block (not float) of the type 5/116/S; so there is still some documentation about.

-Doug

Offline Michael Scott

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Re: 1930 S6 Carb
« Reply #7 on: 14 Apr 2009 at 12:50 »
Eddie
Thanks for the comments
A previous owner had  probably not followed an approprate assembly procedure because there is evidence of a significant repair on the timing cover/inlet manifold. 

Was you referring to the throttle needle or the float needle or both?  I have shortened the float needle as described but I believe that I have the correct throttle needle, supplied by an expert. Throttle response is good for the limited running I have done so far.  I have assumed that I need the level in the carb to be just below the level at which it will flood. It works on a vertical throttle needle!

Doug
I am in email correspondence with AMAL but it takes a long time
Regards
Michael


Offline Michael Scott

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Re: 1930 S6 Carb
« Reply #8 on: 23 Apr 2009 at 15:11 »
Thanks for the various comments and help.

By dint of careful machining I believe I now have the right float needle height.

I have taken the advice re air leaks and regasketed the timing cover and inlet manifolds after careful use of feeler gauges.

The result has been remarkable!  Now putting some miles on - short trips and the back to base to tighten various errant nuts and screws and then slightly longer trips with a scuttle back to cure oil leaks.  I have not yet failed to return to base. (asking for trouble for making that statement!)

Happy riding
Michael