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E: Engine What Carburettor are you using on your racing Comet?


davidd

Well Known and Active Website User
VOC Member
In AHRMA, Carleton and I ran the Amal Mk2 34mm (smoothbore if possible). At the time the rules allowed it, but the Indian guys protested us even though we were not in the same class and AHRMA changed the rule to allow a Mk1 Concentric (R1034). I found one of these 34mm carbs, but I never used it as I went back to the 32 mm 10TT9. I sold the 34mm Concentric to David Tompkins, who says it is running great (37 BHP with Mk2 cam). He is on the cover of MPH this month.

I have run the 36mm (R2036) smoothbore on the dyno, but it is not legal. It made over 41 BHP. If you can run a Mk2 carb I would run the smoothbore (no idle screw). I think the street version would do very well, also. Then the Mk1 concentric.

These carbs seem to provide good performance and they are easy to get and everyone tends to know them and the issues they have.

David
 

vibrac

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VOC Member
We have been stuck with 1-3 /16 TT for years on the comet as that's the 1948 rule and apart from gardener which we did not get on with that's all there is. but i think on the twin we will go for the next sixties date line so the GP will be available my thoughts are 1-3/8 partly because I already have one just need another
 

Nulli Secundus

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VOC Forum Moderator
We have been stuck with 1-3 /16 TT for years on the comet as that's the 1948 rule and apart from gardener which we did not get on with that's all there is. but i think on the twin we will go for the next sixties date line so the GP will be available my thoughts are 1-3/8 partly because I already have one just need another
I think Ian Bain's Norton, Mike Farrell's Rudge and Tony Perkin's Rudge (the methanol one not mine) have much larger TT 'Amals' that are homemade. They rarely enter BHR events and if/when they do I am not sure if they get championship points.
 

vibrac

Well Known and Active Website User
VOC Member
I think Ian Bain's Norton, Mike Farrell's Rudge and Tony Perkin's Rudge (the methanol one not mine) have much larger TT 'Amals' that are homemade. They rarely enter BHR events and if/when they do I am not sure if they get championship points.
Yes I think they may come from Roger Moss I think he needed one for his Scott but since they seem allowed and I think GP's came out in 50-51 it does seem a bitof an onerous suggestion
Anyway the day they outlawed bump starts was the day big carbs and silly compression ratios started to change the sport. I still say that was the safest and most interesting way to start a race. (said he remembering how many steps it took to bump a twin up the grid at Snetterton)
 

timetraveller

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VOC Member
Without wanting to muddy the waters here there are some other things that need to be considered. One is how experienced a racer are you? If you are just starting off then mid range torque and reliability come into it. If both you and the bike are really on top of the situation then there is at least one person using an inch and half GP and revving to 8,000. Is the bike otherwise sorted, for example have you fitted a John Emmanuel steering head, with a modern damper, and have you got the rear suspension sorted out with better springs and damper? I know that I get made and sell the JE steering heads but I sell them at cost so I am not trying to get you to spend money with me but almost all the UK based racers still using the stock chassis have bought the JE steering system.
 

Nulli Secundus

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VOC Forum Moderator
It wasn't really a suggestion Tim. I was just pointing out what others have done and seem to get away with. My Rudge has the 1 3/16" TT.

I think Ian Bain made at least his and Tony's carbs, or got them made. Ian would know Roger, so it could be that they are all involved, but only they will know for sure.

I did only one race meeting at Brands Hatch in 1983 on my 500 AJS and enjoyed the bump starts. Being a lot older and less fit I would not relish the prospect of bumping my Rudge that has more get up and go combined with a quick action throttle.

We are getting away from the original topic for Ben's Comet.
 

davidd

Well Known and Active Website User
VOC Member
The Flash came with an 1-1/2" GP for the big port head. Coburn kept the carb from the BSA Goldstar that he traded to Sid Dickson when he swapped the Goldstar for the Flash. He installed a smaller carb on the BSA. It worked exceptionally well. I do not know what rules Ben is trying to meet, so I stuck with 34mm and smaller.

The TT carbs work well. They are easy to set up and very simple to tune. The GP and Dellorto take some skill to tune. There is a learning curve. Even if you tune them on a dyno, the dyno guy needs to know what he is doing. Not so with the more ubiquitous Amals.

You have to replace the slides, needles and jets every year if you are really racing. That can get expensive with hard to find parts. You also want have extra parts and different combinations available to use. This means it is nice if the parts are widely available.

I got very high BHP out of this 1-7/16" the first time on the dyno. But, without a large selection of slides, needles and jets I could not tune it to run well on the track.
100_0275.jpg
I went back to the 32mm 10TT9 and did well enough for podium finishes in the national championships. With everything else going on I did not have the time and money to devote to developing the carb, manifold and exhaust to get the maximum power and tractability. On the other hand, I was getting everything out of the other carbs I was using because they were so well known and easy to get parts for.

The 32mm TT:
32mm Flash 1.jpg
The 34mm Concentric:
34mm Tompkins 1.jpg
The Mk2 smoothbore:
100_0011.jpg
The 1-1/2 GP on the big port head ( I have the wrong angle float bowl on it):
DSCN3377.jpg
The manifolds are fabricated on all of these except the 32mm 10TT9, which is stock Grey Flash.

I did run an 1-1/4" clip fit GP for a while. I can't remember the issues I had with it, but the 10TT9 seemed to work better. When I sold my racer to Randy Hoffman I loaned him the 10TT9. When I got it back he ran the GP, but told me the 10TT9 was better.

David
 
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ericg

Well Known and Active Website User
VOC Member
David, I'll use the same 1034 concentric on my road going 600 Comet project.
Can you help with jetting datas if you can remember the details?
Thanks.
 

davidd

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VOC Member
Eric,

I would be happy to. I will have to look it up and check with David to see what he changed during the dyno runs.

David
 

Grey One

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Non-VOC Member
Which is Egli Type !. Cheers Bill.

The Egli Comet is a development where money is not a problem. Current machines are using the Gardener carburettor at a severely down draft angle, in keeping with the general angle of the port. I do not know the exact size, but Patrick Godet used a similar instrument of 40 mm diameter for his Grey Flash racer.
The picture is of the Egli Comet at the 2019 Classic TT View attachment 28899
 

Bill Thomas

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VOC Member
Which is Egli Type !. Cheers Bill.

The Egli Comet is a development where money is not a problem. Current machines are using the Gardener carburettor at a severely down draft angle, in keeping with the general angle of the port. I do not know the exact size, but Patrick Godet used a similar instrument of 40 mm diameter for his Grey Flash racer.
The picture is of the Egli Comet at the 2019 Classic TT View attachment 28899
Sorry, I should have used more words, Mine was a reply to TimeTrav',
But Nulli got in a reply before me, So mine did not make much sense.
Ben's Bike is an Egli type, I don't think he wants to spend too much,
He had a problem with the running last year.
I think he just wants to do small stuff , Like Hill Climbs etc,
And I think he is still looking for a Chopped Twin Engine. Cheers Bill.
 

Ben Langton

Active Website User
VOC Member
Thanks for the information and pictures (davidd).
I barely touched the bike for several months except for the odd start up. About a month ago I pulled the cover off and thought I’m going to give it another go. It started well but did the same jumpy lurching at 1/8-1/4 throttle but seemingly fine everywhere else. I dropped the size of the needle jet and it seemed slightly better but still jerky. I decided it was time to file the slide to try and lean it a little more (now running below standard specs speaking with eurocarb for a similar sized engine?) So I took it down about .5mm and assembled with great anticipation. Well it ran terribly again. I must have had it apart with different set ups 10 times.
I telephone the rolling road tuner and yet again no call back as promised. I was really hoping to get it sorted.
So I’ve actually got a Amal R2036 I’m hoping you have some setup info davidd please?
It’s pretty good shape with a 280 main and 120A needle jet but I’m missing a needle.
I’m going to get this thing going better, hopefully.
Thanks again all.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Sorry Ben, It's hard to use the right words sometimes.
I think you are going for Mk1, Which is fine, I have found the settings on the site I sent you very good to start with, But I like, And am playing with Mk2s now.
The only thing is, With the Mk2, If you are a size too weak on the slide, It's like an OFF switch !.
And the pilot jet and screw , Has a bigger effect for higher up the rev's, So if it's a bit rich, You can trim back a bit on the pilot.
2 other people have put in print the same as I have found.
If you use the Mk1, Be sure it already has the slot in the float bowl by the float needle,
So soon as the float needle lifts, The petrol comes out the side,
There is a bit about doing that mod', In the web site I sent you.
Good luck, Bill.
 

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