Funny ole world… Amals vs Mikunis…

Fast Eddie

Fast Eddie

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Funny how we are all in a mad rush to fit Mikunis etc to our Commandos these days…

Here’s a pic of a big bore Honda 400/4 Spondon race bike from the 80s… zoom and and you’ll see the bank of mk1 Amal concentrics fitted as an ‘upgrade’ to the Japanese carbs…!

Funny ole world… Amals vs Mikunis…
 
Now that is in the barn find catagory, probably put together with whatever was at hand. Look at the dogleg in the lefthand inlet. The rightmost one will be the same. I wonder how it ran....
 
Fitting Amals to Japanese bikes was fairly common in 1970s, when someone intended to go racing.

Never seen it on a road bike.

It makes you think there may have been a performance advantage at full throttle/peak rpm and that may have been at the expense of everything else we want from a carburettor.
 
Back in the 70s a local bloke to me had a much modified Honda cb750 road bike
It had 4 MK1 concentrics fitted
He was always flat out on it with a howling 4-1 exhaust
I don't suppose he was worried about a good idle or carb wear or balance
 
kommando said:
That plus CV vs throttle slide directly connected to the right hand.
Click to expand...
Funny you should say that
I've often wondered if a CV would work as a slide carb
IE drill/tap the carb top fit a cable to the slide
Remove the butterfly
You'd probably have to block the transfer port that works the diaphragm 🤔
You should then have a carb that flows a 1/3 more air
What am I missing?
 
Amals set up right are a very good carb, yes they have their little quirks and pilot jet blockages if let sit but they are a simple carb and if jetted right will give good high performance even with worn out slides they still run good, I have tried other carbs in my time on my Norton, but I have found my Norton runs so much better with my old Amals, jetted right for the work that is done to my motor and with the big fat spark from my Joe Hunt both work so well together and no matter how long it sits always fire up first kick.
So a set of Amals on a jap race bike back in the days might have been a good high performance improvement, who knows as I never mucked around with Honda 4s as all my mates brought them new when I went the Norton way.
My mate Ken had a 1970 GT 750 Ducati that came from the factory with Amal carbs, when we dragged each other flat out he couldn't pull away from me and the same I couldn't pull away from him on my 850 Commando, but we had fun trying it was always a race to see who got the jump to the first corner up in the ranges, both of us in our late teens, RIP Ken I miss you old mate.
 

baz said:
Funny you should say that
I've often wondered if a CV would work as a slide carb
IE drill/tap the carb top fit a cable to the slide
Remove the butterfly
You'd probably have to block the transfer port that works the diaphragm 🤔
You should then have a carb that flows a 1/3 more air
What am I missing?
Click to expand...
The WHOLE IDEA of a CV carb is to only open as much as the engine can digest at a given RPM.

What you propose, would be an exercise in time wasting. Bolt on a VM44 Mik instead and have a ball


www.ebay.co.uk

Genuine Real Mikuni 44mm Round Slide High Performance Carburetor Carb VM44-3 | eBay UK

Mikuni's VM Series, round slide carburetors have proven themselves as the performance standard for use on single and multi-cylinder, motorcycle and ATV vehicles. These carbs are designed to work on both 2-stroke and 4-stroke engines.
www.ebay.co.uk
 
concours said:
The WHOLE IDEA of a CV carb is to only open as much as the engine can digest at a given RPM.

What you propose, would be an exercise in time wasting. Bolt on a VM44 Mik instead and have a ball


www.ebay.co.uk

Genuine Real Mikuni 44mm Round Slide High Performance Carburetor Carb VM44-3 | eBay UK

Mikuni's VM Series, round slide carburetors have proven themselves as the performance standard for use on single and multi-cylinder, motorcycle and ATV vehicles. These carbs are designed to work on both 2-stroke and 4-stroke engines.
www.ebay.co.uk
Click to expand...
Yep I realise how a CV carbs works and the reason behind them
But I suffer from an overly active imagination 🤣🤣🤣🤣 and I already have VM 42 sitting on the shelf plus a complete drouin kit
 
Fast Eddie said:
Funny how we are all in a mad rush to fit Mikunis etc to our Commandos these days…

Here’s a pic of a big bore Honda 400/4 Spondon race bike from the 80s… zoom and and you’ll see the bank of mk1 Amal concentrics fitted as an ‘upgrade’ to the Japanese carbs…!

View attachment 121079
Click to expand...

Raced a 500 with 4 Mk2s back ni the day, used the 400 bottom end for the 6 speed box, everything else was Yoshi, full Formula2 spec
 
baz said:
Back in the 70s a local bloke to me had a much modified Honda cb750 road bike
It had 4 MK1 concentrics fitted
He was always flat out on it with a howling 4-1 exhaust
I don't suppose he was worried about a good idle or carb wear or balance
Click to expand...
Actually, in the 70, they cost so little that there was no real reason to worry about wear!

In 1970 my single carb Triumph 500 was stolen (my only transportation). So, I got a $50 basket that came with a bad head. The local Triumph shop only had Daytona heads in stock so I needed two carbs and the associated cables and throttle. As poor as I was, I considered them almost free (the head on the other hand took many weeks of lunch money and sweeping the floors and other drudgery in that Triumph shop.)
 
Fast Eddie said:
Then why isn’t it fitted to Commando ?

And why aren’t we being shown pictures ?

And why aren’t we privy to detailed write ups about ?

Must try harder…
Click to expand...
It has around 6 projects in front of it
I did start to fit it many years ago
But my 750 runs so well I'm loathed to mess with it
It's not the best type it's an early twin belt one
The later single belt kit is a lot better but was still a nightmare for most people
I've been looking at extending the impeller shaft to convert it to a single belt plus fitting deep groove ceramic bearings etc etc
The plus side is next week I start working part time instead of full
This will hopefully give me some more workshop time and maybe some of my ideas will reach fruition 🤔🤔🤔🤔
 
A well-tuned carburetor will always improve performance. It probably does not matter what it is. In Australia, many of us raced using methanol. The improved performance probably came from less criticality in jetting. Amal carbs are a British invention - like cricket. They require a lot of patience. Japanese motorcycles of the 1960s and 1970s were more about commuting than racing. A 650SS Norton is a very different motorcycle than a CH750 Honda - on a race track, it would make any CB759 look stupid. The CB750 Hondas which were competitive, usually had CB450 pistons in them. There has only been one CR750 Honda in Victoria - Tony Cacciotti rode it - it had race cams with 4 megaphones - a thrill a minute.
When you use methanol with Amal carbs, you can drill the needle jets. The needle jets in Mikuni carbs are much more complex - they affect throttle response - so on a CB750 Amal carbs would be cheaper, even when using petrol.
 
When TD Yamahas first came to Australia, we were not used to tuning motorcycles so lean. Many people do not seem to realise that aspect is just as important with a four-stroke.
 

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