AMAL PREMIERS STICKING

Guido said:

Maybe if I hone the first 1/2"from the top. Would that cause a air leak? I'd really like to find a way to fix the out of round a better way than honing.

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Don't hone the bores. They will remain out of round, get sloppy, and more than likely become more problematic than they already are.

Anything else I have to say about Amal carburetors would just cause a ruckus.

Are you running heat insulators on the carb to mani flange? Ive had slide stick wide open at a fuel stop, prior to restarting I noticed my quick pre twist didn't return to home position. Touched carb boil to find it too hot to keep a finger on it more than a second. This was a single amal carb setup and the 2in1 mani is a lot less able to shed heat compared to two single manifolds. After a short wait, the slide released and never rejammed while underway. I put it down to heat soak while stopped.
In your case, perhaps upper bores distorted from excess heat. Insulators can be had in two thicknesses. I now run the thicker type, at both ends of each manifold for peace of mind. Bowl no longer get hot.

Guido said:

Really truly the only way to set them up is on the bench. Too crowded while on the bike. I did notice that the right carb was a tight fit getting the screws in the tops and that bolting the setup to the head after all screws were tight may have distorted them.
I'll mess with them some more today.
Maybe if I hone the first 1/2"from the top. Would that cause a air leak? I'd really like to find a way to fix the out of round a better way than honing.

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Confirm that you are tightening the gantry to carb tops first and that the carbs to manifold and the manifold to head have some play and are not tight?

Another look at the straightening jig.

I'm not a fan of that medieval stuff.
What is the point of bending the flange back then refitting a cantilever O-ring so it repeats somewhere in the future.
#
With the gantry it would be much safer to mount the (new) carburetors to the manifolds on the head and without O-rings so they can seat to check things for any form of binding or loading.
The four gantry fixing holes need to have some clearance on the fasteners at that point otherwise any drama across the manifold faces will transfer to the gantry mounting (and they can be a firm fit on the bench) which is not a problem in stock fitment and dual cable.

How the top of the slide bore could become out of shape enough to bind the slide is odd, the casting is not that fragile.
It could be doctored with a suitable jacking bolt but would have some risk.
I personally would not remove any material from the body.

Time Warp said:

I'm not a fan of that medieval stuff.
What is the point of bending the flange back then refitting a cantilever O-ring so it repeats somewhere in the future.
#
With the gantry it would be much safer to mount the (new) carburetors to the manifolds on the head and without O-rings so they can seat to check things for any form of binding or loading.
The four gantry fixing holes need to have some clearance on the fasteners at that point otherwise any drama across the manifold faces will transfer to the gantry mounting (and they can be a firm fit on the bench) which is not a problem in stock fitment and dual cable.

How the top of the slide bore could become out of shape enough to bind the slide is odd, the casting is not that fragile.
It could be doctored with a suitable jacking bolt but would have some risk.
I personally would not remove any material from the body.

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I don’t think this is right. The one point you need it rigid is at the top of the carbs. That’s the only plane you can trust. Tighten there first then manifold and carb body because those don’t need to be crazy tight.

Amals have been distorting at the top forever.

If someone was going to the expense of the DP single cable gantry and new Premiers ( $600/$650 here) you would want to make sure there is no stress passed on as in the horizontal plane the gantry plate is going nowhere.
If you are refitting carburetors or new carburetors the line across the two manifold faces come into play also.
#
The set up in general can be improved.
An insulator is used at the Norton head but the cap screws allow heat soak from the head to the manifold. (Moto Guzzi of the same period used Bakelite inserts and washers to stop that transfer at the studs. (Also on the Amal equipped Loop engines > iirc)

Triumph used a similar set up at the manifold to carburetor but that was changed in the early 1970's (iirc)
The small section O-ring (like the Norton) was superseded to a larger section, stepped studs and a rubber and cap under the retaining nuts as an extra barrier to heat soak and to some degree to change the harmonic to the carburetor itself (vibration)

All things can be maximised with a little time and effort, I have never had a Amal problem going back to 1978 though, luck maybe.
I did machine the 4 gantry fixing holes larger so they had some movement before tightening on new Premiers.

MichaelB said:

Amal de-warping jig

Found this tool posted on the BB forum while searching for info on my A65, I believe the bike has the original carbs (no drain plug in the float bowl), and they are in OK shape aside from the stuck slides, so I fabbed this up and it does the trick. I warmed the carb bodies up a bit, and used...

www.accessnorton.com

Warped Amal Concentrics - is there really no cure?

As many of you will know, the Amal Concentrics (mine are 930s) are very sensitive to over-tightening of the flange bolts, which causes the body to def...

www.britbike.com

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This is the proper way to straighten them, avoid removing material from the flange or slide bore

Its a design problem. - the Amals are too thin and they warp. Best solution is to go to a better carb. There are twin carbs available that don't have problems.

I got it all sorted. Turns out if I pinched with my fingers at the top of the bore I was able to get the slides to move freely. Just that much pressure and I was able to get them to slide.
So I took a jubilee clamp and placed it around the top and gave it a tighten up. Now they are both moving freely.
I did not leave the clamp on.
Turns out when the gantry was bolted to the right carb the left carb did not sit flush against the bottom of the gantry.
There was a 0.10 gap at the rear of the bore but touching the front of the bore.
Took some doing but I got it to function smoothly.
I used everyones suggestions so collectively everyone was right on the money.
I have had this bike since '76 and I am still learning new things.

I started it up and let it run till hot and still running smooth.
Now my head gasket is leaking as I saw a puff shoot out from between the head on start up.
Can win for losing.
Thank to all

Guido said:

Turns out when the gantry was bolted to the right carb the left carb did not sit flush against the bottom of the gantry.
There was a 0.10 gap at the rear of the bore but touching the front of the bore.

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How is this possible?

swooshdave said:

How is this possible?

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Carb body machining tolerances?

Can‘t really blame Amal though, tolerances twixt mounting flange and carb top angles just don’t matter as standard, but do with the gantry set up.

More likely Manifold machining of angles is off.

Mismatched or deformed insulators.

kommando said:

More likely Manifold machining of angles is off.

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Or that. Still wouldn’t matter at all with the stock configuration.

As already mentioned by a few posters, rubber mounting the carbs would also ‘solve’ the ‘issue’ of minor miss alignment of the carb tops caused by such.

Glad you got it worked out Guido. I recently acquired the gantry , apparently to fix a problem I don't have.
I do like the idea of the single cable run, single idle adjust, syncro etc.
I needed new cables anyway, so why not.
I had mocked it up on a spare set in a vise to get a head start on what can go wrong when you posted up.
Thank you for your past as I will pay close attention to these details on the install.
I want to play around with the jetting a little before final install.

Fast Eddie said:

Carb body machining tolerances?

Can‘t really blame Amal though, tolerances twixt mounting flange and carb top angels just don’t matter as standard, but do with the gantry set up.

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Yep, I think often there is a tendency to "blame" Norton (or AMAL) when some aftermarket part that the bike was not designed to use either doesn't fit properly or causes some other issue. This situation is a good example. I had to enlarge the holes in the gantry to ensure no binding/misalignment/warping of the carbs when I installed it. THEN I discovered the fastback tank (Burton Bike Bits) would not fit down over the gantry! So I got the opportunity to un-install it!

With the gantry there are a couple of tweaks I would have done first.
That thumb screw for the idle probably should of had either a hex head or a socket head for a allen wrench as the one it is shipped with is too hard to turn.
The hole for the vac balance tube could have been a slot so as not to kink the hose.
Other than that it is what the carbs needed to keep in sync.
I also enlarged the hole in the gantry too.

I have the same setup as being discussed here. New (last year) Premiers and recently installed Gantry - I needed to replace the throttle cable, so why not try Don's Gantry.
During setup, I found the same issue as Guido, carb tops not in the same plane. There is enough clearance in the manifold hardware to cause this - a little twist one direction or the other can cause the carb tops to not be co-planar. Loosen manifold screws and give them a bit of a twist... working with the 2 angular surfaces can create a lot of movement.
Just fiddle with it till you get it right, the Gantry is an excellent piece. Idle is much more stable than with the old (and probably worn out) two into one cable.