C15 - replacement carburettor?

[Tris]

Hi - I've inherited a 1961/1962 BSA C15 which I've stripped and rebuilt (my first time working on classic bikes).

Sadly the carb - Amal Monobloc 375/34 - has seen better days and there are many things wrong with it. To replace the parts/repair it I may as well buy a new carb as the cost would probably be equivalent.

I've found I can buy the exact same Amal 375 but am wondering if there is a better alternative I could/should go for?

I'm not looking to restore it 100% accurately I just want it to run reliabily, I've already switched out the original 6v ignition/distributor for 12v digital/electronic.

Any advice greatly received, thanks.

[B Murphy]

I used a 24mm PWK Flatslide Power Jet Carb for one of my C15 builds which worked much better than the standard Amal.

[Tris]

Thanks for the reply, I'm kind of looking for as much as a drop in replacement as possible.

That looks like it would need some modification and/or tuning? Unfortunately I know nothing about carbs.

[AdrianS]

Buy the one originally fitted. They worked then and they work now.
The Amal's are quite expensive and it is tempting to try cheaper offerings. I have previously tried but reverted back to the original fitment as they were better. If it was a race bike, then that's a different story........

[Tris]

Hi - I agree the old Amal's are very expensive. The original Amal Monobloc is £250+ to replace.

According to the Rupert Ratio book, the newer concentric which was fitted to later C15 models is "of better internal design than the Monobloc".

I can get a Concentric for a fraction of the price of the Monobloc, I'm just unsure how much tuning is required?
I honestly don't care about fuel economy/performance. My bike currently doesn't start properly due to the original Monobloc carb which is falling to pieces.

[chaz]

bit of a contradiction, you want a straight forward drop in , not interested in extra performance/economy and no extra tuning. buy the original, anything else will be trial and error.
Ive got a Mikuni on my A50, different manifold fixing and rubber couplings, cables, hoses,feed pipes.
you dont want to pay for a new one, only one (or two) real answers. rebuild yours or buy a used one from ebay.
with todays sources, ultrasonic clean, rebore the body, fit new plated slide, new jets and gaskets kits all available.
Ive recently sold around 8 or 10 Amal's on ebay (still got 2 on there) all useable none went for over £100.
the other option let someone else have a look at yours.


or buy a new one at a classic autojumble ,sometimes easier to negootiate a deal

[Beesy]

I'm sure I read that the Amal concentrics can be used as a replacement for the Mono blocs.

If you don't want Amal, how about a Wassel carb. I don't have any experience of them, but they are plentiful and cheaper

[DAVE BRADY]

Hi,

I would suggest a new carb. and if a saving is to be made then get a concentric.  No amount of cleaning or fitting of new parts will be as good as new carb.  Ultrasonic cleaning may remove all the crud in the minute air/fuel passage ways but it will not put back the material that has worn away over the years.
If you go down the road of a new concentric then ask the supplier to jet it for your bike.  The likes of Surrey Cycles will do this.  Also, there are many C15 riders out there with concentric carbs fitted to their bikes and I am sure that they will share the jetting info. with you.  This forum exists for this purpose.

Dave.

[Tris]

Hi Chaz - apologies I didn't mean anything to come across as contradictory. I really appreciate the advice/help.

As I said in my second post, I don't know a lot about carbs. I have however learnt from experience that the original part is not always the best.

I would be happy to pay for an original new one if it was absolutely worth spending double the money to get the original part.
Amal don't have any stock of this carb and I can only find one place in the UK which says in stock. However, having dealt with them quite recently just because their website says in stock it doesn't always mean that it is. I will be calling them tomorrow to double check this anyway.

My current one has the following wrong with it that I can see:

• Mixing chamber top - thread is ruined, new body?
• Throttle slide heavily worn/ridged
• Jet needle worn
• Float bushing missing
• Float cover and screws need replacing

To clarify, by drop in I mean I don't need to fabricate any parts/brackets for it to fit the bike. If it needs some basic tuning as in turning screws to get the right mixture/idle etc then that is perfectly fine. I just don't want to start drilling jets/milling pieces.

Cheers

[Tris]

Hi,

I would suggest a new carb. and if a saving is to be made then get a concentric.  No amount of cleaning or fitting of new parts will be as good as new carb.  Ultrasonic cleaning may remove all the crud in the minute air/fuel passage ways but it will not put back the material that has worn away over the years.
If you go down the road of a new concentric then ask the supplier to jet it for your bike.  The likes of Surrey Cycles will do this.  Also, there are many C15 riders out there with concentric carbs fitted to their bikes and I am sure that they will share the jetting info. with you.  This forum exists for this purpose.

Dave.

Thanks Dave - this is super useful thank you so much.

I did put it through my ultrasonic cleaner, however I believe the carb is too badly damaged for it to be worthwhile repairing.

[Tris]

I'm sure I read that the Amal concentrics can be used as a replacement for the Mono blocs.

If you don't want Amal, how about a Wassel carb. I don't have any experience of them, but they are plentiful and cheaper

Hi Beesy - yeah I've seen these in my hours of trawling the web this weekend. They claim to be identical to Amal?

I believe my options so far are this:

Try and source original 375 Monobloc - £250-£270
Replace with Amal concentric - £120-£140
Replace with Wassell - £75-£95

[Beesy]

Just re-ead my Amal catalogue. It says the concentric carb is a superior replacement to all previous Amal Carbs.

So if the Wassell us comparable to the Amal you can see a few quid.

Like I said I've no experience of Wassell but they look tempting. Especially if it's only for a few thousand miles a year

[chaz]

I fitted a pair of Wassells to my T100 Triumph, had no probems with them and as they are a passivated finish, shouldnt have any ethanol problems.
not being funny but customers want a £35 battery as its cheaper than a £65one, the difference one lasts a year or two the other 5.



Ive sent a pm to you

[cdsdorset]

A wassel carb would be OK (fitted one on the wife's Enfield) . A lot depends on how much you intend using the bike, if it's only occasionally Sunday jaunts the wassel will be fine.
If you want to use it a bit more frequently go for the concentric and ask Surrey Cycles to jet it for you. Dint forget you will also probably alter the throttle/choke cable.

[Tris]

Yeah it's definitely just going to be a Sunday bike - nipping out for a local coffee etc, probably not going to do many miles at all.

I think I'm just going to take a punt on the Wassell.

Thanks to everyone who responded, much appreciated.