Carb for Comet

[redbloke1956]

I am a big one for NOT re-inventing the wheel, so rather than acquiring several carbs and comparing them, I thought I should throw it out there and see what you are all using.
My 52 Comet will soon have 8:1 cr, B-TH mag, new Mk3 Cams.
I want to be able to cruise comfortably at 65 MPH and still have some left for playing .
What carb are you guys running on a Comet, or what do you think would be suitable to get a few more ponies

Kevin

 

[davidd]

The carb alone will not get you much when compared to what cam and the exhaust mods will yeild in terms of HP. I would use something new whether it is an old one or a modern one. The tuning and performance will be much better. I have had good success with the 30 mm MK 2 Amals on my Rapide and I have run 34 mm on the racer. Without other preparation, I would not go higher than 32 mm on a Comet.

David

 

[nobby]

I use an Amal Mk1 932 on the 500 engine and an Amal Mk2 Concentric 32 mm on the 600.
Both have 'hot' cams, the 500 is a nervous engine in city-traffic, the 600 is a 40bhp engine and is fantastic in every speed.
If you need an adapter, Jim Moser is the man. Link is here.

 

[Black Flash]

if you are not crazy about originality, go for a Mikuni VM series. Really high quality stuff and easy to tune with jets and needles really cheap. these things will last a very long time before they clap out.

Bernd

 

[chankly bore]

I have a standard Comet with an overhauled Type 29 carburettor, Mk3 cams and an unrestricted exhaust (nearly straght through) and I have a 21" front wheel, therefore the speedo IS accurate.My thing is happy at 60 m.p.h.The piston is about 8:1.In your place I would go for a straight through pipe or "silencer" and a 30 mm.or 32 mm. Mikuni. The Vincent head was designed for 72 octane and about 6.8:1 compression,so without a different head you are pushing a snowball uphill with pointy-toed shoes as far as extracting performance.I think a lot of 70 m.p.h. Comets have 19" wheels on the front-if you take my meaning.Sure any good Comet, mine included,will sit on 65, but get off the major roads,slow down, stop worrying about the interstate truck sitting on your clacker and enjoy what the 'bike was designed for.Just remember,a lot of it is 60 years old.By the way,some owners locally say that premium fuel will reduce your chances of a nip-up.Ignition advance 35 degrees BTDC maximum!!Cheers,F5AB/2A/7945 since 1970.

 

[soloman4040]

Have you tried upping the gearing? On long hauls I have a 46 sprocket on and take it up to 70 in 3rd and snick into top, to cruise. Sound harsh? for normal pottering I admit the 48, is better and more comfortable but a 46 works for me obviously only one up. I am able to manually control ignition.
John

 

[jim burgess]

On the Shadow I have 8:1, straight through exhausts, MK1 cams, MK2 Carbs at 30mm, and it really goes well. No probs with the carbs except they tend to stick open in damp weather, (teflon on the slides is the cause). On the Norvin, 7.3ish:1, straight through pipes, MK2 cams, MK1 Amals at 30mm and I have no complaints, but I have to wind it up a bit more I assume that is the cam.
Cheers
Jim

 

[nkt267]

What carb are you guys running on a Comet, or what do you think would be suitable to get a few more ponies

Still no definitive answer to this question though.
What carb? what slide?? jets etc
By the way Kevin, the twin brigade didn't get in early with the 'Buy a twin' quip. John

 

[davidd]

I do not think there is a definitive answer to the question. Small choke carbs work better at lower RPM and larger choke do well at higher RPM. The Mk II cams work well at 4000 to 6000 rpm and less well below, but so many owners use them on the street that their street performance must be acceptable. They also work better with no silencer. If a silecer is used a 105 cam is probably a better choice. A Comet would gain an advantage by spinning up higher than a twin due to its design, but many prefer lower RPM riding.

The jetting and the cut-away would seem to me to be very machine specific items. They depend in great part on the bike's silencer, pipe, and cam. I think many of the Comet riders can supply general information that will be very close, which is a good place to start. Nobby has a great deal of experience with singles and I believe he is generous with any specific information. Once Kevin decides on his preferences and the equipment I think that he will have plenty of help.

David

 

[nobby]

I already have sent the following information in a PM, and added a few things.
The cam in the 600 is an ex-race cam from Australia (or a Terry Prince one, do not have confirmation about this), the cam in the 500 was a Robinson 105, but also modified by an 'expert' for racing. I did race the 500 engine for a couple of years, so many parts were modified. Hence the nervous character. If you only go for the 30 or 32 with a Mk2 cam I think the performance will improve and it can stay smooth with the correct silencer.
If you go for a bigger carb, check out your tank, some petrol tanks wont allow a bigger carb. If so, I have somewhere a longer and straight 32mm inlet, leftover from racing. That way a 932 carb will stick out a bit, see picture.

I use the long megaphone-like SS Supertrapp, the sound is marvelous and the performance also. 39.8 bhp on the dyno is not bad for a street-Comet, is it?
Until the sidecar disaster during the Annual at IoM, all engine work was done by a professional. After that event my wife did not leave me, but the pro was kicked out! I did the 500 engine myself, totally rebuild it with new and some second hand spares. It took me probably 10 times the amount of time because I am not a mechanic. But I did it, and when it was back on the street it started right over and was running almost 100%. I bought the 600 engine in Australia with the great help of Neil Videan from an ex-racer (do not know for being allowed to enclose his name) and kept it running perfectly and fast so far. It was build with great expertise so I did not have to do a lot actually.
Therefore it makes me proud to be called 'having a great deal experience' by an expert like David Dunfey.