AMAL PREMIERS STICKING

[Guido]

I have the new premiers fitted. When I first got them one was sticking when the throttle was opened. I sent it back and they said the bore was out of round. They fixed it and it was fine for awhile but then it started sticking again. So today I took them off but the slides wouldn't come out. They just jammed near the top. I finally got them out and with my bore gauge they both measured 0.10 thou out of round.
I didn't over tighten the tops or the manifolds at all as I was warned about that when I first got them.

My question is, how do I get them back round again?
I should also mention I have the Madass gantry set-up installed.
I am thinking the holes in the gantry may be misaligned and causing it to bind

 

[RoadScholar]

loosen the gantry and ancillaries or remove the mechanical link(s) to the slides and see if they move freely.

Based on what you wrote I would think the out of round bore you mentioned might make my suggestion above null and void, but possibly worth a try.

Best.

 

[swooshdave]

When you say that you don’t overtighten the carb to manifold what is your criteria for tight?

When you got the carb back from Amal we assume tested it before installing?

Are you saying both slides are sticking now?

 

[RoadScholar]

When you say that you don’t overtighten the carb to manifold what is your criteria for tight?

Good question.

You may have used equal torque, but too much equal torque leads to the same destination. I'd be inclined to check the flanges and the manifolds for flatness. You can do this, initially, by removing the "O" ring and seeing if the two surfaces for mating correctness. The down side is that if both surfaces have the same set they will appear to mate correctly, so try the with the correct orientation then try a 180 fit if this isn't diagnostic then put them on a flat surface and see if (and what size) feeler gauge slides under.

The way to check the torque is to bring the nuts down until the carb just stops being able to be moved by hand then backing the self locking nuts of about a 16th of a turn. Final check is to put the slide in and insure that it moves freely through it's full stroke.

Best.

 

[Torontonian]

I use 2 lb. test torque on the carb. to manifold nylock nuts . That's next to nothing. Nylocks only for this light tightening. The more you tighten the more you risk carb body warpings. Go easy.

 

[Guido]

What is out of round is near the tops of the bores. The slides when in the bores slid fine at the bottom, it's just near the top. I can pull the slides up to just 1/2" below the matting surface of the top of the carb before they bind up. I am thinking it's not the manifold connection but the gantry holes where the screws go through and thread into the top of the carb. I am going to drill out the holes in the gantry to allow for expansion. Those holes are too tight and doesn't allow them to expand when the engine is hot.
As far as how tight are the manifold? Just snugged up tight, not ham fisted tight.
Beside there is no way that makes sense because that is on a whole different part of the carb and should affect the top of the bore.

My question is, how do I get them round again.
So kind of tubing expander?

 

[swooshdave]

When you overtighten it distorts the tops.

I would not drill out the gantry.

I recall seeing a rig to straighten the carbs. Probably on this forum. Search and if you don’t find it I can try to look tomorrow.

 

[Time Warp]

It might not be the case here, but one of the first things you do is remove the manifold studs and lap the face so you know it is flat.
Countersink the threaded holes before refitting the studs.
Having an O-ring for a seal generates a potential problem in itself which can be part of the distortion problem to the carburetor flange.

 

[jan nelder]

What is out of round is near the tops of the bores. The slides when in the bores slid fine at the bottom, it's just near the top. I can pull the slides up to just 1/2" below the matting surface of the top of the carb before they bind up. I am thinking it's not the manifold connection but the gantry holes where the screws go through and thread into the top of the carb. I am going to drill out the holes in the gantry to allow for expansion. Those holes are too tight and doesn't allow them to expand when the engine is hot.
As far as how tight are the manifold? Just snugged up tight, not ham fisted tight.
Beside there is no way that makes sense because that is on a whole different part of the carb and should affect the top of the bore.

My question is, how do I get them round again.
So kind of tubing expander?

How near to the top do slides actually go with all components in place?... that’s all the clearance needed.

 

[Esmerela]

"My question is, how do I get them back round again?
I should also mention I have the Madass gantry set-up installed.
I am thinking the holes in the gantry may be misaligned and causing it to bind"

I would mount the carb my lathe and use a boring bar to clean out the ovality.

I expect the holes in the gantry are in perfect alignment CNC precision and all, however in all honesty the carburettors would only be eyeball close at best. Bolt up flange joints against the head manifolds and carburettors compressed gaskets insulators and o-rings it's a big ask for perfect alignment at the carburettor tops. IMHO the Madass set up would really benefit from a rubber inlet stub to take the stress away from the carb tops.

 

[Fast Eddie]

I also recall seeing pictures posted on here of a straightening ‘jig’ used to strighten the mounting faces and, if that was the cause of bore distortion, correct that as well.

In the absence of such a device, or a lathe and boring bar like the posh lads (and lasses Esme), the last sticking carb I sorted for a mate I did simply by hand, on the mounting face and bore, using wet and dry to remove metal from the tight spots in the bore, then polished the bore. It solved the problem. I believe a heavy chrome brass slide helps too.

I also had to lap in in the slides in some brand new mk2 Amal’s recently, in this case the slide was sticking towards the bottom, a much less serious issue, but still not right.

Guido, carbs that stick open are very dangerous, so you need to sort this out one way or t’other...

 

[ludwig]

Rubber mount the carbs.
Ditch the O ring.

 

[Deets55]

The carb manifold to head bolts should be loose when tightening the gantry screws to the carb body. Don recommended to leave at least one side loose, I left them both slightly loose. There is a slight rotational play that needs to be accounted for to make sure the carb tops are flat to the gantry. After the gantry is snugged up go back and tighten the manifold to head bolts.

 

[oldschool]

I tried the Madass gantry on my Mk3 and could not get it to work smoothly. No amount of loosening, realigning and tightening would allow free movement of both slides. The only time when both slides moved freely was when the carb mounting bolts were actually loose.......
I emailed Don and he suggested that the carb inlet tubes may not be identical, or the face of the inlet mountings on the head may be out of alignment.
Too much trouble for me, so I sold the kit.
This is not intended to drift off-topic; I am just suggesting that the gantry kit may be indicating a problem somewhere else in the carb set-up.

 

[MexicoMike]

If they stick now but didn't when first installed, it is likely that, as other have said, that excessive torque SOMEWHERE in the carb(s) fittings has warped the body. If the gantry assembly is putting any strain on the tops, that would seem to be the first place to look. I am not personally familiar with the gantry, at least operationally. I wanted to be and ordered one but it would not fit under my Fastback tank.

 

[maylar]

If the gantry relies on the carbs being an exact distance apart, be aware that all Norton intake manifolds were not created equal. I put a pair of NOS in-the-Amal-box manifolds on my Norton last summer and my crimped stainless braided fuel line would NOT fit. The carbs are about 1/16 inch closer together than they should be. I suspect that the flange of one or the other was ground off center.

 

[Seeley920]

Take the carbs off the bike, set them up with the gantry on the bench and test then

 

[MexicoMike]

Yep! You could also leave the carbs attached and take the gantry off the carbs and see if the slides will move up/down freely. If either method results in the slides moving freely, do some work to enlarge the gantry holes slightly and then attach/snug the bolts holding the carbs to the manifold. Then install the gantry/tighten the gantry-to-carb screws, ensuring that there is some side-play between the gantry /carb screws just prior to the point where the screws are snugged down. IOW, you want the screws to freely drop from the gantry into the fittings at the top of the carbs without any side-interference that would cause warpage when the screws are tightened.

OF course, as noted, you can warp the bodies by over-tightening ANY of the screws/bolts associated with the carbs, even if all the mating surfaces are true/aligned!

Also, it is possible that if the carb bodies are warped, releasing the screw/bolt pressure on them may not return them to the non-warped state.

 

[RoadScholar]

I suggest that you get the carbs off the bike and off the manifolds, remove the cables, springs and the needles. The slides should simply drop in and not stick at any point of their stroke. If the sticking is still evident then go from there. The point is to reduce the number of variables as much as possible so you get as close to the root cause as possible.

Best.

 

[Guido]

Yep! You could also leave the carbs attached and take the gantry off the carbs and see if the slides will move up/down freely. If either method results in the slides moving freely, do some work to enlarge the gantry holes slightly and then attach/snug the bolts holding the carbs to the manifold. Then install the gantry/tighten the gantry-to-carb screws, ensuring that there is some side-play between the gantry /carb screws just prior to the point where the screws are snugged down. IOW, you want the screws to freely drop from the gantry into the fittings at the top of the carbs without any side-interference that would cause warpage when the screws are tightened.

OF course, as noted, you can warp the bodies by over-tightening ANY of the screws/bolts associated with the carbs, even if all the mating surfaces are true/aligned!

Also, it is possible that if the carb bodies are warped, releasing the screw/bolt pressure on them may not return them to the non-warped state.

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.