Mk1 Concentrics (26mm)

Howard

Well Known and Active Forum User
VOC Member
I'm sorting out a few minor problems on a "new to Vins" friend's Rapide.

It runs well enough, apart from very low down, but I think that's due to adjustment and cable sync. My question is, has anyone used 26mm carbs on a Rap, they seem very small, and I seem to remember Amal recommending Mk1s should be a size bigger than predessesors.

H
 

greg brillus

Well Known and Active Forum User
VOC Member
Hi there Howard, I don't see it being an issue, unless the pilot circuit is too small. It should have good torque off the line, but perhaps run out of steam as the revs get higher. Mind you the cost of new Mk 1's is cheap enough to go bigger if he wanted to. When I spoke to Burlen's recently they said that their sales of original type Mk 1's has dropped in favor of the more superior "Premier" range which now includes a model with an aluminium body over the normal Mazak bodied carb, and the cost difference was very little over the original type. May be of help, who knows.............:).......Cheers..........Greg.
 

Howard

Well Known and Active Forum User
VOC Member
Thanks Greg, I agree, it should make a nice torquey tourer. I'd never heard of that size carb on a Rap, and I was probably comparing with my twin's 32mm which is only 6mm on diameter, but 50% more area.

It's not going to be raced, so I'll leave well enough alone for now.

H
 

Bill Thomas

Well Known and Active Forum User
VOC Member
Just picked up a pair of 1" monoblocs with Vin 'Manifolds, I think they maybe a bit small !!, A new world for me !!. Cheers Bill.
 

Bill Thomas

Well Known and Active Forum User
VOC Member
I bored out a 15/16" Monobloc , To a bit over an Inch, How the OZ rap' took there's out to 30mm I don't know !!, For the Comet the other day.
It ran like a Pig !, Very rich, I weekened everthing , But in the end I had to cut a 6 slide, Went out and was not happy, I can't see how an 1. 1/16 Mono on a Rap, Runs 240 main jet, And yet an 1.1/8th Concentric runs 200 ?. I gave up in the end, The weather was too good to miss, So put my old E.I. back on.
I will try a 240 main etc when I get time. Cheers Bill.
 

Albervin

Well Known and Active Forum User
VOC Member
Absolutely no comparison with slides and main jets on Mk1, 276 and Monobloc. All totally different from the ground up. I remember a Victorian chap (now deceased) was getting over 65mpg (Imperial) on Monoblocs while riding like the wind and others on Mk1s were struggling to achieve 50mpg trying to keep up. I have 276s and was in between those figures BUT the jet sizes varied from 170 to 240 on all the bikes. I run 170s and that is a little bit rich. Then again our fuel is called Petrol but bears no relation to National Super Benzole of 1965!
 

Bill Thomas

Well Known and Active Forum User
VOC Member
I had another go Sunday, Better but still not right, If it lets me down in the Forest, It's a Long Walk !!.
I put the settings for a "D" Rap', Apart from a hand cut 6 slide, Went back to a 5 slide = Way Too Rich.
I used to be good at this, But I have lost my touch !!.
I might try a 25 pilot, If I can get one.
The engine is Flash spec', Has gone well in the past, But like me, It's past it's best !.
It might be the manifold I made to go with the Rear Head, It was a quick Lash Up, I made to get a Comet to a Special Rally about 18 years ago !!, And it's still on there !, Shame on me !, It might be Pooling ?.
Amal says this Rubbish they call Petrol, Makes the bike run weak, But all mine have gone too rich.
I am running a standard float, But somebody, 40 years ago !, It's been under my bench since then !, Cut the brass bit on the float, To bend it up to get the float down a bit, To make it weaker !, I tried that one, but no good, I wonder if that was why it was under the bench !!.
I need a rolling road !!, The people who live near me are giving me Bad Looks !!.
If they think the Comet makes too much noise, I will get the Twin out !!.
Cheers Bill.
 

Howard

Well Known and Active Forum User
VOC Member
Absolutely no comparison with slides and main jets on Mk1, 276 and Monobloc. All totally different from the ground up. I remember a Victorian chap (now deceased) was getting over 65mpg (Imperial) on Monoblocs while riding like the wind and others on Mk1s were struggling to achieve 50mpg trying to keep up. I have 276s and was in between those figures BUT the jet sizes varied from 170 to 240 on all the bikes. I run 170s and that is a little bit rich. Then again our fuel is called Petrol but bears no relation to National Super Benzole of 1965!

We went on a quick section run last year, a Rapide with pre Monoblocs got 50 mpg, my Egli (admittedly lighter) did 60 mpg on 32 mm Mk1s with 260 main jets, there's just no consistency in results.

H
 

Albervin

Well Known and Active Forum User
VOC Member
I had another go Sunday, Better but still not right, If it lets me down in the Forest, It's a Long Walk !!.
I put the settings for a "D" Rap', Apart from a hand cut 6 slide, Went back to a 5 slide = Way Too Rich.
I used to be good at this, But I have lost my touch !!.
I might try a 25 pilot, If I can get one.
The engine is Flash spec', Has gone well in the past, But like me, It's past it's best !.
It might be the manifold I made to go with the Rear Head, It was a quick Lash Up, I made to get a Comet to a Special Rally about 18 years ago !!, And it's still on there !, Shame on me !, It might be Pooling ?.
Amal says this Rubbish they call Petrol, Makes the bike run weak, But all mine have gone too rich.
I am running a standard float, But somebody, 40 years ago !, It's been under my bench since then !, Cut the brass bit on the float, To bend it up to get the float down a bit, To make it weaker !, I tried that one, but no good, I wonder if that was why it was under the bench !!.
I need a rolling road !!, The people who live near me are giving me Bad Looks !!.
If they think the Comet makes too much noise, I will get the Twin out !!.
Cheers Bill.
Bill, if your stuff is anything like our petrol then start by dropping jet size and/or needle. Most slides need "fettling" as a 3 3/4 seems about right for me. Just look at what Howard wrote; no sense in it at all.
 
Top