Fitting New Carb

[Howard]

I brought an Amal Concentric Carb for my `51 A7. The carb came with an "O" ring that fits in the carb flange however  originally the bike had a gasket between the head and carb. Should I use the o ring set up or a gasket ? 

[MG]

I'm using a 930 Conc. on the Flash with a 3mm thick Tufnol spacer as a heat barrier AND the O-ring on the carb. No leaks at all with this setup.

Cheers, Markus

[Goldy]

If it,s got an O ring then you don,t need a gasket, but as MG says the tufnol gasket is very good for preventing heat transfer to the carb which prevents all sorts of odd running faults.

[BSA_54A10]

I toss the O rings as well but I use a thick soft gasket which will compress and partially fill the hole where the O ring went.
Most important is how tight you do it up.
When done up correctly you should just be able to twist it a bit on the mounts ( allows for expansion )

[iansoady]

That's right, many people do them up far too tight. I always use single coil spring washers and do them up so the washer is just compressed.

I also use the thin gaskets between tufnol spacer / drip shield and drip shield / head joint, with a light smear of grease.

[Howard]

Thanks all....regards Howard

[Colsbeeza]

This is an old thread, but interesting all the same.
The Monobloc on my 1960 A10 iron head was running perfectly until the then-new slide stuck in the up position. Fortunately the mag cutout worked perfectly. That was back in May before I had my knee replaced, and I spent the last few months fitting the electric starter. In using emery paper on the slide and body ( as gently as possible) to just ease the tightness, I have created running issues with rough hot idling, minor backfiring, stalling when hot etc, possibly exacerbated by the more retarded ATD modified for the starter.
It seems that I have been over-tightening the mounting bolts ( not studs in my case) in fear of air leaks and have distorted the body. I have been spoiled rotten by the perfect performance of the old carb, so temporarily gave up and ordered a new carb - accompanied by another black look from the missus. . ( I want to keep the old carb and see if I can find someone to resleeve it ).
Amal's advice ( or my interpretation) is to do up the bolts /studs / screws with a spring washer so that the spring - quote "just flattens and the nuts ( bolts also presumably) should be tightened until the clearance between the carburettor flange and the manifold surface is no less than 0.025 inches at all points". Surely this would also depend on a new O-ring? It doesn't sit well with me that you have to be so gentle bolting up a flamin' carby. I'll bet the average rider back in the 60's was far more hamfisted.!
I have a 3mm insulating washer against the head and use gaskets either side of the drip tray with a smear of grease and hope the O-ring seals against the outer gasket.
I am contemplating chucking the outer gasket and rely on the O-ring against the metal of the drip tray.
Just like to hear others thoughts on fitting the carb and guarantee no air leaks.??
Col

[muskrat]

G'day Col.
Yes ditch the outer gasket.
With my new 932 I do it up (new O ring) till the carb just touches the manifold. The problem with having a drip tray and gasket is not having enough tension to seal them.
Cheers

[Rex]

I use the new O ring and the various gaskets. I also use lock washers on the fasteners and nip them up tight "enough".
That is, not swinging on the end of a 6" spanner, but not leaving the carb on finger-tight fasteners either. I reckon anyone would need to be severely challenged in the skills department to do up the fixings sufficiently to distort the carb body enough for the slide to stick.

[trevinoz]

Col,
There is a bloke in Douglas Park who does a good job, I have had a few done by him.
Don't be tempted to go to the local bloke, I have seen some of his efforts and none of them were any good.

[Colsbeeza]

Hi Rex,
Then I must be "severely challenged in the skills department". 
Trev, I will PM you for that contact. Thanks
Col

[groily]

I thought (maybe wrongly?) that the 'tight flange sticky slide' thing was more a concentric problem than a Monobloc one?
I've not had problems with Monoblocs myself,  but have had some hassle with concentrics.
I've heard it said 'finger-tight plus a flat' with a spring washer - but having had a concentric almost fall off on one of mine, I don't reckon that is quite enough absent gorilla hands. It's awkward to lose a flange nut miles from home  . . .

[Rex]

Hi Rex,
Then I must be "severely challenged in the skills department". 

As Groily says, it's apparently a thing with Concentrics, but the more chunky design of Mono's must make it a rarer occurrence.
I thought you were saying a previous owner had done it?
I recently had "sticky slide syndrome" on a 389 fitted to a Venom, and it wasn't a distorted body.
 It wouldn't drop the last 10mm and even when pushed down it needed freeing up again with a screw driver it was that tight. Witness marks showed it was the inside of the slide holding up on the "jet block". Five minutes with a removed jet block, the slide and with some polish soon sorted it though.

[Colsbeeza]

Hi Rex,
Your Venom experience rings a bell. When my new slide stuck in May, I could not get it to drop without dismantling it at the time. Up on the lift and months later after knee op, I removed the carb and pushed the slide up and down. I found what you found - slide sometimes catching on the jet block. The jet block was tight, so I gently filed the inside edges of the slide, but also found that the slide was quite tight from about halfway upwards so that the spring would not push the slide down easily. Carb is original 1960-fitted and the new slide had slight tightness but it must have got worse since I re-fitted it recently after the electric start exercise, so suspected that I may have contributed to that by overtightening (according to AMAL guidelines but not my guidelines).
I gently emeried the slide with 1200 wet & dry and a tiny bit from the inside diameter of the chamber until it was free enough, although not entirely free. Interested to know what polish you used? I might give that a go. Maybe polish is a better approach, as it would better target the tight bit.
Col

[Rex]

The polish is some wonder-stuff the mrs bought from a shopping channel, and I nicked it..
Pretty generic stuff I would think, Col. It looked and smelt like Autosol too.