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Mikuni carb vs Combat engine 72 commando

 
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NortonPete



Joined: 27 Jul 2004
Posts: 3
Location: Northern New Jersey

PostPosted: Sat Aug 07, 2004 11:42 am    Post subject: Mikuni carb vs Combat engine 72 commando Reply with quote

What a great forum. This is my first post.
I've owned a 72 Norton for 15 years but 10 of those years the
bike sat in a garage. I owned a '72 in '74 but this bike I bought
one day in 89' from a Vietnam Vet who couldn't start it anymore.
I know he was a performance freak.
While reading this forum I have learned more than I did in 20 years
of owning a Norton.
When this bike ran it was unreliable and finally in '92 it cracked the
cylinder walls. I took it to a shop that I thought knew about them.
I got a call during the repair that the pistons were oversize for the
new standard barrels. I ordered new standard sized pistons.
From reading I now realize that this engine is a Combat engine and
I probably put a standard barrel and piston on it.
I just now figured out that the Mikunis are 34 mm.
What should I do? I'm not changing the cylinders or pistons.
What will happen with a Combat head on standard sized cylinders?
What should I do with these Carbs? Replace them? With what?
Thanks in advance
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eyeguy
Guest





PostPosted: Sun Aug 08, 2004 4:54 am    Post subject: Reply with quote

Hello and welcome
I run a 72 Combat here in the UK with a 34mm SINGLE Mikuni carb. It's easy to start , idles perfectly, and enjoys great torque, and is only a smidge down on top end when compared to a twin carb setup. IMHO if you want to enjoy it as opposed to fiddling with it, I would get hold of a single carb manifold and set it up.

Have fun( and fit electronic ignition!)

Paul
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PostPosted: Sun Aug 08, 2004 5:23 am    Post subject: Reply with quote

Paul,
Thanks for the reply.
I understand about the torque vs highend and the
need for a different manifold for the single setup.
Is the single 34mm Mikuni different than one of the two
I now have? Could I use one of my carbs or would it be
smarter to just buy all new?
What about having standard cylinders and pistions with a
Combat head? Is this now just a detuned engine.

And a bit of humor:
Norton's where always considered the
pinnacle of the motorcycle world in the 70's. We used to
laugh at anyone with a Harley.
( Good exercise bike while pushing it down a road. )
The fellow who sold me the bike had just refused the last
2 or 3 people's offer because they didn't know enough about Norton's.
I just had an offer from a fellow but he didn't know anything about
Nortons so I decided to keep it and restore it.
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illf8ed



Joined: 30 Dec 2003
Posts: 475

PostPosted: Sun Aug 08, 2004 6:43 am    Post subject: Combat Reply with quote

The combat engine didn't have special pistons or cylinder although the cylinder was painted black rather than silver. The differences from the standard engine were the combat head with .040" milled off for higher compression and 32mm intake ports. It also has the double S camshaft and 32mm Amal concentric carbs instead of 30mm. The engine cases were altered with stronger internal webbing and the "combat" engine breather, dropping the oil sump filter.

You can run a single 34mm Mikuni with little performance loss until you get into the highest rpms. The twin 32mm carbs are better at the high range.
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NortonPete



Joined: 27 Jul 2004
Posts: 3
Location: Northern New Jersey

PostPosted: Sun Aug 08, 2004 8:29 am    Post subject: Reply with quote

David, Thanks for the reply.

I guessed than that the original owner had bored out the cylinders
and put oversized pistons in. I suspected that but got confused
when looking at the Norton parts manual.
It shows two different part numbers for the "standard" vs "Combat"
pistons. I guessed that they must have been bigger.
But you are correct the parts manual shows two different part
numbers for the cylinders but than says "silver" or "black"
no mention of size difference.

This info has helped me greatly as to where to go with the bike.
I do have Boyer Bransden ignition.
I took it out for a spin the other day after draining the gas and
changing all oils. Ran real good. Just the chrome is pitted.

Thanks again. Good riding to all.
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eyeguy
Guest





PostPosted: Mon Aug 09, 2004 1:07 am    Post subject: Reply with quote

Hello again
I believe that one of your Mikunis should be fine, you could try Allens here in the UK as they are Mikuni specialists. Then, sell the other one on E bay!

You can also reduce compression by using a thicker head gasket, which brings it back to standard spec, and, if you're still runiing the original pushrods, gives those an easier time too, as well as your knees.

Have fun

paul
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The Unapproachable Norton Commando

At the end of 1967 the Norton Commando was announced.

The Norton Commando was greeted with a certain amount of scepticism because on first sight the commando appeared to comprise of the old Norton Dominator twin cylinder engine mounted at an inclined angle in a set of new cylinder parts.

It was not realized that the new Norton Commando Isolastic method of engine suspension damped out all engine vibration and produced a machine which had uncanny smoothness for a vertical twin. In due course the critics were silenced and the Norton Commando had the distinction of being regarded as the first of todays so called superbikes. There can be little doubt that the original design concept of the Norton Commando has proved correct, since comparatively few modifications of any real consequence have been made since production commenced during 1968.

Now nearly 40 years later Norton Commando riders like us are a breed of our own, and as far as we are concerned its still more fun to go for a blat on the old Norton Commando, and fast. As a Norton Commando owner and enthusiast, my goal here is to promote and give credit to those who keep the Norton name going.

It is more deserving to give credit to the Commando itself, for after all these years it continues to be respected. The original Commando designers like John Favill are those who deserve the credit for developing this incredible motorcycle.

The Norton Commando Roadster and Interstate of the late seventies, never died. Although the Norton Villiers factory dispersed the tradition lived on. Today Kenny Dreer in the USA is developing the new 952 CC Norton. What a great looking bike this is, and its engineering is still based on the original layout. It will be interesting to see how the new 952CC Norton does in todays tough motorcycle market. One thing is for sure, I would own one if I could afford it.