Pre-Monoblock Carburetor

[Geoff Leake]

Hello guys,

My early B33 (1947) which I'm in the process of restoring is in need of a carburetor. As I understand it, the O.E. fitment was an Amal type 289G. I suppose I could repair the one I have if I could source the parts but that might work out more expensive than getting a replacement. Does anybody have a decent used one of this type, or any good spares for sale? Alternatively, what's the view on moving to a more-readily available and seemingly cheaper Monoblock? Any tips/advice would be greatly appreciated. Cheers.

[scifi]

Well if you can repair your original, you would save over £400 on buying a new one.   The only thing which might be worn is the slide, which again can cost £65 or more.    https://amalcarb.co.uk/pre-monobloc.html   stock some of the parts.
   
If all else fails, just measure the carb's diameter, and fit a cheaper newer carb, which has been jetted correctly.   I think the flange bolt spacing is pretty much standard for those inlet diameters.

[Geoff Leake]

Hello Scifi, thanks for advice.

Having measured it with the vernier I'm fairly confident a new slide will do the trick. However, my restoration, whilst not concours, is pretty extensive and the body of the existing carb is completely worn through to the brass and would look right out of place with the rest of the bike. I'm not too fussy about replacing the carb with the same as the original (as you say, very expensive) and I'm not concerned about criticism from the tyre kickers either! So I'm feeling the best route would be a different, less expensive carb. Monoblocks appear to be much more readily available, would you advise going for one of those?

[scifi]

A few of my older bikes have the Concentric Carb replacements, which are cheaper than the monobloc.   Also my 350 RE Bullet has a Mikuni, which is most modern and cheaper still, also it has a great cold starting device, which gives first kick starting.   The Mikunis do have a different main jet numbering scheme, so best of luck with that..!

[Geoff Leake]

Thanks again Scifi, looks like I could be going for a concentric. Cheers.

[cdsdorset]

If going for a new concentric the wass⁰el equivalent is good value. I might have a good used amal concentric.

[Geoff Leake]

Hi cds, thanks for the note.

I looked at the Wassel and was considering it. Having said that, if your used concentric is good and useable without any issues, I could be interested in that. Also, to say I'm not particularly technical is an understatement! So assuming the flange measurements marry up, if I used a concentric or Wassel in place of the O.E. type, is it simply a case of ensuring the jet sizes in the replacement correspond to the to originals?

[Mike40M]

As far as I know, jetting will be different on pre monobloc, Monobloc and Concentric. Guess partially due to different fuel level.
Only problem I've had with old pre monoblocs is leaking float valves. Leaking carbs can cause fires. So why not try the old one you have first?

[Geoff Leake]

Morning Mike, thanks for your advice, I wholeheartedly agree a fire is to be avoided at all costs! And I appreciate I can easily use the original carb effectively simply be buying a new slide. The reason I'm hesitant to do so is that the body of the old carb is in a very poor state and in my opinion, will significantly detract from the overall appearance of the finished restoration. That's why I'm leaning towards an Amal concentric. Member, Cdsdorset implied in a post earlier this week that he might have a decent concentric for sale, but I've not heard anymore from him since 28th February.

[cdsdorset]

Hi. Sorry been a bit manic here. Afraid i only have a spare monobloc.

[Geoff Leake]

Morning cds, Thanks for letting me know; and no need to apologise, we all get busy from time to time. I think I'd prefer to use a concentric. However, if I can't find a suitable one, I might have to consider a monobloc. If that turns out to be the case, can you confirm your monobloc is in good useable condition? And if so, how much would you want for it? I hope to hear from you soon. Thanks.

[Stevegayler]

Geoff. An old carb is worn. Don't mess about with old carbs. Buy a new one.

[Geoff Leake]

Hi Stevegayler, On reflection, I think you're right. On the subject of Wassell carburetors, I've heard conflicting reports on the quality of these. But bearing in mind it'll be fitted to a very early B33 (1947 rigid), so we're not looking for high-spec/super-duper performance, just something that functions properly. Do you have an opinion?

[rhyatt]

have you tried ringing BURLEN in Salisbury ??
very helpful carb people

https://amalcarb.co.uk/catalogsearch/result/index?p=4&q=289

[Stubaker58]

From what I've read part of your reason for changing the carb rather than repairing the old one is the look of the thing.  I reckon if that's the case then a (new) Monobloc would look better (more in keeping) than a Concentric, the Concentric might look just a tad too modern?
Just a thought.