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Vincent Comet Concentric Carb

youngjohn

Well Known and Active Forum Website User
Non-VOC Member
Hello all, this is my first post.
I've just acquired a Comet with a 928 concentric carb fitted and it seems to be running a bit on the rich side. Can anyone give me any advice on, or tell me base settings for main jet, needle jet, needle and slide? Main jet at the moment is 250 and needle jet is 106.
Thanks.
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Hello John, Sorry nobody seems to be talking to you, It's because it's been done a lot of late and no two Vins are the same,My comet is only a load of odds and bits and even has a rear cyl' head off of a twin with a lump of exhaust pipe for an inlet manifold !!. Settings depend on the state of tune, size of pistons, type of cams, type of exhaust, + lots of other things. thats what owning a Vin is all about!!, You will be playing with settings forever. The petrol you buy now has changed and some people, OK me, Have found it makes the bike run rich on the slide. Slides are cheap, I have took a file to make the cutaway bigger, ie weaker,Base settings,Pilot 30, Slide 3 1/2 to 4 , Needle 106, Main 220, Float height will affect it a lot as well !. There is a lot of info' on www.thevincent.com, Good luck Bill.
 

Albervin

Well Known and Active Forum Website User
VOC Member
In the top right corner of this page is "advanced search". Type in Comet Carb settings or 928 Concentric. You will get a few ideas from the results that it depends on a whole range of things from the type of silencer to cams & compression. Remember that if it is running rich at less than 3/4 throttle you should be playing with needle position & slides. Main jet is for full throttle & anyway, a little rich will save your piston.
 

derek

Well Known and Active Forum Website User
VOC Member
I had a lot of trouble with rich running on my overhauled Comet new 928 concentric, I found that the normal 11/2 turns open of the pilot jet was far too rich, mine runs nice at 3/4 turn open. I also filed the no3 slide to make 31/2 to 4. It is not yet run in, so as for the medium to full bore settings i will wait and see.
 

youngjohn

Well Known and Active Forum Website User
Non-VOC Member
Many thanks for all your help. I have stripped and cleaned the carb and found that the pilot jet was only about 1/4 turn open. Rebuilt, it seems to be running fine now.
 

derek

Well Known and Active Forum Website User
VOC Member
I realise that my previous answer may seem wrong, as the pilot adjuster controls pilot air and is weaker when screwed out, but as mine would not run evenly at 11/2 turns the throttle screw needed to be adjusted up and the richness was was because it was the coming onto cutaway control. by adjusting the pilot into 3/4 turn open the throttle adjuster could then be lowered and a very even slow tick over achieved. The slidewas the filed to 31/2 to 4 to achieve smooth transition from pilot to cutaway control.
I hope tha this makes sense.
 
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