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.
I used a 24mm PWK Flatslide Power Jet Carb for one of my C15 builds which worked much better than the standard Amal.
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.
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........
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.
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
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,
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.
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
Quote from: DAVE BRADY on 09 Jan, 2022, 10:24
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.
Quote from: BEESY on 09 Jan, 2022, 10:20
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
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
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
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.
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.
Allen's Performance do Mikuni kit direct replacement for C15 carb
https://www.allensperformance.co.uk/carb-kit/carb-kit-listings/
If you buy a wassel it will probably come set up for a different bike and you may need to reset. Don't forget about cable differences.
I've got a Wassell concentric on my D14 Bantam. Works fine.
Try also Hitchcock for a monobloc. They have good stock and will jet accordingly. I bought one for my B40, bolted it on and there was an instant improvement ( not as much as having the lollipop distributor rebuilt though).
I bought a brand new carb for my B44 from Amal direct and it's beautifully engineered. Amal are in Spitfire House, Castle Road, Salisbury, Wiltshire SP1 3SB (Tel 01722 334221). The Amal part number is the same as the original 1967 carb but has Amal's own seat modification for lead free petrol. The other thing I was pleased with was the first class service I received from them and their expert advice at the other end of the phone. A rare thing these days!
Buy British and go to Amal.
that said, I bought an Amal from Salisbury and had to go back to India (its where they are cast and machined now) as when Salisbury tried to build it they couldnt, incorrectly bored, took extra month to get.
I bought a concentric carb to fit to my C15 only to find it wouldn't fit with the original air/battery box.
Just to throw other thoughts into the equation (on the same basis as the £35 battery vs the £65). I have had lots of fun (not!) over the years sorting out carburrettors on lod machines (I amigain like many here). I make some points about Amals (as I tend to stick with those on bikes) but have SUs and Webers on my 4 wheeled vehicles (both have good and bad points.
What I have discovered and hope you find it helpful:
Old original Amal concentrics are made of Mazak (aka Zamak) and because the throttle slides were originally of very similar material they wore badly and if you were not careful when fitting them to the inlet manifold they also often distorted the flange leading to air leaks and sticking slides. For this reason you should be careful buying second hand concentrics.
Monoblocks fared better and the ones I have had were brass slides (which also wear) so if you have a good one (however it sounds like you do not) I would work with that.
At present I have a modified (for 4-stroke) 1038 concentric on my ABSAF 600 GS using solid brass slide, adjustable stay up float, aluminium Viton tipped needle and nylon coated throttle cable. The flange is straight and body not worn, jetting is correct. It is hard to imagine a carburettor that works any better.
Float needle:
(https://amalcarb.co.uk/media/catalog/product/cache/d712142dd130cc1ec7cd4f3e0857497e/image/8362ae89/light-weight-aluminium-needle-valve-with-viton-tip.jpg)
Adjustable float (see the brass tang for fuel level adjustment):
(https://i.ebayimg.com/images/g/K8MAAOSw6rhdRB2d/s-l1600.webp)
On my ZB34GS I also have a pretty new 930 concentric with a new Amal coated slide and the same adjustable float and aluminium float needle and Viton tip.
Pic of the coated slides:(https://i.ebayimg.com/images/g/acUAAOSww51lJA4T/s-l400.jpg)
Newer Amal concentrics are made of cast aluminium (not Mazak) have coated slides as standard, the light weight Viton tipped float needles.
All these things add up to a carburettor that works well on an old motorcycle (there is loads of info on settings - as mentioned if you go to Surrey Cycles or similar and tell them what it is for, whether you have an air filter, different compression etc (all things that affect the settings) they will supply you with the correct instrument.
The Wassell carbs are just like the original Concentrics (AFAIK) and will almost certainly develop the same problems, given time and use and personally I would go with a concentric carb (Amal or Wassell) with the goodies I have pics of.
My next task is to get the ZB running properly with its correct 10TT9 once I have rebuilt it.
Remember to use petrol pipes suitable for Ethanol petrol and ideally if the bike is standing to any time empty your carb and petroltank as it will rot the inside of your tank and fur up your pilot jet making starting and low speed running almost impossible when you come to use it again (scan the fora for people having these issues.............)