Getting the mixing chamber off a pre monoblock carburetor

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Invicta
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Getting the mixing chamber off a pre monoblock carburetor

Post by Invicta »

Hi Gents. I am trying to remove the mixing chamber from the carburetor of my 1949 model 18. Looking at the vice grip marks already on the nut it looks as though someone has either done it up very tight to stop it leaking , or has tried to undo it in the past. I have gripped the body in the vice with soft jaws and tried a very large spanner on the nut but it will not shift. I have soaked it in WD40 for several days but to no avail. Has anyone got any ideas how to undo this . I am afraid to try too much force for fear of damaging the aluminium alloy body. The nut is brass. I am not sure of the different coefficients of expansion of brass and the carb alloy so don't know if heat will work. I will give it a try though.
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Rob Harknett
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Re: Getting the mixing chamber off a pre monoblock carbureto

Post by Rob Harknett »

http://archives.jampot.dk/technical/Car ... 5-1956.pdf
Here's a parts list. The fitting you refer to is 14/060 It should have a fibre washer on the bottom end against the flange. I would not try too much heat myself. Dump the carb in a pot of diesel and get on with something else for a week or so. Also, if you have the top off, make sure the bowl is also full of diesel.
SPRIDDLER
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Re: Getting the mixing chamber off a pre monoblock carbureto

Post by SPRIDDLER »

It may be stating the obvious but I've found that rather than applying steady and increasing pressure with the spanner a sharp hammer tap on a well fitting spanner often breaks the joint with surprisingly little force.
You do have to make a sympathetic judgement with regard to how hard to hit the spanner. I've made a rough 'n ready holder which saves clamping the carb directly in the vice but you still risk distorting the flange/body. Ideally there would be a steel plate 'twixt the wooden holder and carb as the soft wood will crush a bit and add to the risk of distorting the body but I only use the holder because I have to fettle one-handed.
Carb holder.jpeg
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Last edited by SPRIDDLER on Wed Mar 27, 2019 1:23 pm, edited 3 times in total.
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Rob Harknett
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Re: Getting the mixing chamber off a pre monoblock carbureto

Post by Rob Harknett »

Yes a sharp tap often works Nevvile, bit like the old villiers flywheel that had a special hammer tight spanner, holding the flywheel and using a normal spanner almost impossibly, The spanner had a lump on the end to hit, one tap shocked the nut loose easy, to then undo by hand. Same should help on the carb, but I would first try soaking it for a few days in the hope of it working on oxidisation.
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clive
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Re: Getting the mixing chamber off a pre monoblock carbureto

Post by clive »

If at all possible reattach the carb to the engine as this will give it something to hold it steady. Use a ring spanner and as suggested a sharp tap may free it. I never manged to fre one off the bike.
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Mick D
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Re: Getting the mixing chamber off a pre monoblock carbureto

Post by Mick D »

Hi

I'm assuming you're referring to a 276 Amal pre Monobloc carb:
276 Carb.png
WD 40 is not a penetrating fluid, (despite what people say), the best penetrating fluid I have used and my 'go to' option is a 50/50 mix of ATF and acetone - used in conjunction with heat, (from a propane torch in my case), there's little it won't resolve.

Not sure if it's item 36 or 47 in question but if 36 I'd try gently tapping around the thread whilst hot and soaked in penetrating mix - tapping can help to break the 'crud' bond and permit the penetrating mix to do it's job.

If it is item 47 and penetrating mix / heat / shocking the spanner doesn't work I'd look to drilling off the head, removing the float chamber and then tackling the thread, (which will now not be under tension.

Regards Mick
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Invicta
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Re: Getting the mixing chamber off a pre monoblock carbureto

Post by Invicta »

Hi Mick , It is item 36 as shown in your diagram that I am trying to shift. The carb body flange was badly distorted and I have filed and faced it flat, it looks as though someone in the past had used a lot of force on it. I will try the diesel soak for several days and see how I get on.. The choke slide was missing and the threaded hole in the top of the carb where the cable fits has been blocked with something. Is it essential to have a choke to cold start these machines. My 1950 model 18 has one fitted and apparently the 1949 model started life with one according to the parts book. I have a BSA C12 that was never fitted with a choke and that always started fine from cold without one. The rest of my bikes have a choke of some description or other.
Regards
David
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