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WM20 has wrong type of Amal carb - refurb or replace?

My newly arrived 1941 WM20 has an Amal 276BP/1J fitted but I understand it should be a 276C/1B.

It won't idle properly and wants to run with the choke on and still dies unless revved so I was about to embark on a strip down and rebuild, possibly sending it off to Draganfly for resleeving but now I have discovered it is the "wrong" carb I am not so sure.

What would others do?

1 - Live with it whilst sourcing the correct WM20 276C/1B carb, which could then be sent off and rebuilt if needed.

2 - Spend the money on the "wrong" carb and get this set up working.

The rest of the WM20 is fairly original, but I'm not going a 100% rivet-counter look. I am more interested in an authentic period feel but usability and reliability are more important.

Any advice would be welcome, as would someone sourcing a serviceable 276C/1B !

Cheers - Simon

email (option): simon@leanmachine.co.uk

Re: WM20 has wrong type of Amal carb - refurb or replace?

Hi Simon

I ran my bike for far too long on a worn carb (worn body, worn slide, warped flange). It didn't do it any good.

I bit the bullet and bought a brand new carb. It completely transformed the bike.

I think there are mixed reviews out there and I am not sure Amal are selling them anymore.

However, mine has done a good few thousand miles now and is still a first kick starter (hot or cold).

Last thing you want for an old side valve is a lean machine!

Regards

Pat

email (option): sacombsashtrees@hotmail.com

Re: WM20 has wrong type of Amal carb - refurb or replace?

Simon a 276 carb is a 276 carb. The other numbers are only to do with specifications which can easily be altered. I'm sure a 1J float chamber is vertical the same as a 1B , maybe the fuel pipe attachment is different?

As far as the rest of it is concerned. As long as you have a 1" bore - 170 main jet - 106 needle jet - 524 slide - needle in position 2. The only difference will be the number on the flange.

To strip and clean it properly, you will need to warm the body and gently tap out the jet block, after which you can clear this tiny drilling and it's corresponding drilling in the jet block with a piece of fine wire. Blow everything else out with an air line and check the flange is flat with wet and dry paper on flat service. Of course it will never work properly if the slide is rattling around in the body like a dick in a bucket. Ron
PS I find it better to buy Amal carbs and spares from "Hitchcococks Motorcycles"

M20_295

email (option): ronpier@talk21.com

Re: WM20 has wrong type of Amal carb - refurb or replace?

Well there are two opposing views!

I will strip the existing carb at the weekend and check it over, including jet sizes and the seemingly notorious idle airways. It appears to be 1" from an Ariel VB.

I have just had a price through from Draganfly for a resleeve and service and this is £175 (I think it is plus VAT so £210 plus postage. Not too bad if it delivers a reliable solution, and I imagine a similar price to a new carb.

The downside of the recon route is having the bike off the road for around 6 weeks.....

Hmmmm.


Edit - update after checking the Hitchcocks and Amal websites.

A new 276 (generic) is £324 inc VAT.

A new 276C/1B from Amal is £289 inc VAT - but they are showing no stock and the item on back order so I have contacted them for a lead time. If it's not too bad I will go this way.



email (option): simon@leanmachine.co.uk

Re: WM20 has wrong type of Amal carb - refurb or replace?

I don't think there's anything opposing about what me and Pat said? I would agree that a new or refurbed carb is the ultimate option. But there might not be anything wrong with your own carb that a bit of your own time might put right.

Worth a try and an education in itself.......If it still doesn't work properly.....Go the expensive route.

I'm surprised that Hitchcocks are dearer than Amal? It was always my understanding that Hitchcocks and Surrey Cycles were selling genuine Amal parts at the retail price indicated by Amal......Obviously not! And something for me to be aware of in the future. However! Amal are notorious for being out of stock and keeping you waiting for months.....Sometimes a year or more.

Hitchcocks idea of keeping carb bodies in stock and building to your requirements, makes more sense. Ron

email (option): ronpier@talk21.com

Re: WM20 has wrong type of Amal carb - refurb or replace?

Thanks again Ron.

I will try to get it stripped and cleaned this weekend and how it goes from there. I know from my Land Rover experience that faffing about with old and worn out carbs (and dizzys in LRs) can be a waste of time.

email (option): Simon@leanmachine.co.uk

Re: WM20 has wrong type of Amal carb - refurb or replace?

I had the wrong carb on my matchless got a new one from hitchcocks which they jetted and set up from there book 1 day for delivery and it runs like a new bike .

Re: WM20 has wrong type of Amal carb - refurb or replace?

276s on old motorcycles are a bit like Bren Guns. You need to be able to strip and clear them in the dark, so best to practice at home.

If the body and / or slide are worn then you have to make a decision about re-conditioning. If it isn't worn then blocked pilot drillings are the likely cause of rough running. They are easy enough to clean but you have to be methodical and thorough. Simply having a poke around and blowing down the likely orifices is not enough.

They are simple instruments and easy to tune and a decent working knowledge of them is really essential to achieving a reliable rideable machine. Even a new one could have problems after a winter standing with old fuel in it.

Re: WM20 has wrong type of Amal carb - refurb or replace?

Regarding worn slides and bodies, what is the best method of inspecting them to determine the extent of any wear? I’m sure anything this old will have some signs of wear but how do you know when it is too much, what wears first the body or the slide? I have seen new slides listed for sale but note there are different grades.

email (option): Simon@leanmachine.co.uk

Re: WM20 has wrong type of Amal carb - refurb or replace?

It's the body that wears most but a new slide can often help. you shouldn't be able to feel any discernible wobble in the slide. However a worn body won't make a lot of difference to the actual running of the engine! But it's getting it to idle nicely that is the usual problem.

I think you have nothing to loose in stripping your carb for a look see. Send some pictures! Maybe spend a few quid on some new parts if it all looks reasonable. Ron

email (option): ronpier@talk21.com

Re: WM20 has wrong type of Amal carb - refurb or replace?

I have looked at the slide and it has 6/3 stamped on the top. It looks worn to me, noticeable wear / a gouge on one side of the lower skirt.

Also, the needle is hanging on the highest setting.

If I was looking at a new slide, how do I tell if this the correct part for a 276bp/1J ? I believe the correct 276c/1b carb has a number 4 slide so do I look for the correct slide for the bike or the carb that’s fitted? I am thinking it should be no.4 to suit the bike.

Thanks once again.

Simon

Re: WM20 has wrong type of Amal carb - refurb or replace?

Yes a 6/4 for an M20. The cutaway at the air intake edge determines the vacuum on the spray tube and each increment of cutaway =1/16" ie a 4 cutaway is 4x 1/16" (1/4"). Ron

email (option): ronpier@talk21.com

Re: WM20 has wrong type of Amal carb - refurb or replace?

Well I have stripped, cleaned and reassembled the carb but given up for the evening as I also had my CBT today and need a rest!

I managed to get the brass jet block out and it looks all clear, as was the tiny idle airway in the main body. I did notice one odd thing in that the hole drilled through the body which the mixture screw goes into is open at the far side. I have a slightly different spare Amal carb body and this hole is plugged with a brass dowel in the spare, but the one fitted to the bike is open at the back. I will see if I can post a picture, but I have temporarily plugged it by screwing in a plastic number plate screw to see what happens.

I have the carb back on the bike but fuel flooded out of the base of the carb when I turned on one of the fuel taps. I will investigate further in the morning and see if I can get it running.


026C6FF0-6D34-4673-B0FA-F66F2FF34EF2

email (option): Simon@leanmachine.co.uk

Re: WM20 has wrong type of Amal carb - refurb or replace?

That's not good. It should be either right-handed or left-handed but not both ! The pilot air mixture cannot be regulated at all if it's open.

Re: WM20 has wrong type of Amal carb - refurb or replace?

I’m wondering how it got like that. Did it fall out, was it pushed out accidentally by someone overtightening the mixture screw or did someone take it out for a reason?

I don’t suppose it matters too much but I guess I have found out why it won’t idle.

I will see how the temporary plug works and then I may need to put grub screw in with some ptfe tape around the thread.

The flange was also distorted from previous overtightennig so I have flattened it out In case it wasn’t sealing properly.

If I can sort out the flooding I hope to be able to set it to tick over tomorrow.

email (option): Simon@leanmachine.co.uk

Re: WM20 has wrong type of Amal carb - refurb or replace?

The hole at the rear of the pilot screw should be open on an M20 at least.

Re: WM20 has wrong type of Amal carb - refurb or replace?

Matty Leahy
The hole at the rear of the pilot screw should be open on an M20 at least.
What?? There should be a plug on the opposite side to the adjusting screw! Unless you mean the tiny drilling? Which I discussed earlier in this thread.

This is a brand new carb I bought from Amal some years ago, and I had problems with the slide sticking from day one. I bolted it to a block of steel and honed it out and it now sits on the shelve as a spare. I'm running with an original carb that Martyn Bratby refurbed for me. Ron
M20_238

email (option): ronpier@talk21.com

Re: WM20 has wrong type of Amal carb - refurb or replace?

I stand (sit) corrected, it's the earlier carb with the four holes around the body that has that open hole.

Re: WM20 has wrong type of Amal carb - refurb or replace?

To see a 276 with the hole opposite the mixture screw tells me that the carby was not running right and someone has compared it to their mates pre war or later post war AJS and certain Norton carbs with the four holes around the base and noticed the hole at the end. So drilled it out thinking it was wrong. If body is marked 76 it is 4 hole type with the open hole opposite the mixture screw. If 276 it has 1/4 inch hole instead at the bottom inside the bell mouth and has the hole opposite the mixture screw blocked. To have needle on top notch means it is running very rich. A new 6/4 slide may help but generally the body is worn egg shaped from over tightening so the new slide is not a smooth fit. Best to get someone like Martyn Bratby to bore out the body and fit oversize slide.

email (option): ukcarbs@hotmail.com

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