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ET: Engine (Twin) Pilot jet


erik

Well Known and Active Website User
VOC Member
My rapide is running very well with the amal concentric mk 1 carbs fitted.But tick over is very poor becaus e the mixture is to weak which means the build in Pilot Jet is to small.Luckily it is possible to fit bigger Pilot jets in the place where they lived decades before.even the thread for the Jet is there.How can i remove the pressed in Pilot Jet behind the airscrew? Regards Erik
 

Marcus Bowden

Well Known and Active Website User
VOC Member
Either drill it out or use a very small BA tap, 8 or 10, screw it in, hold tap end in vice and knock the body firmly & square so not to snap or break the tap, being hardened steel.
Also check that the passage from the screw in jet to the pilot air screw is sealing, I had pilot screws not shutting off the fuel !!
bananaman
 

erik

Well Known and Active Website User
VOC Member
Thank you Marcus,a good idea! I hope I can remove all the debris after Drilling because there is a small chamber with very narrow holes towards the manifold.Erik
 

vibrac

Well Known and Active Website User
VOC Member
I had a concentric and attempting to drill out the jet it fell out and joined the 206 valve circlips in the 5th dimension of my workshop. In the end I gave up looking and on a whim stuck the pilot screw back in, amazingly the bike ran perfectly!
I just dont think these carbs are made to the level of accuracy that say Mikunis (or original Amals were) originality may cover the use of pre monoblock originals or monoblocks but otherwise I use Mikunis now
 

Magnetoman

Well Known and Active Website User
VOC Member
tick over is very poor becaus e the mixture is to weak which means the build in Pilot Jet is to small.
Several questions come to mind. Instead, worn slides can cause poor tick over so how do you know it's too lean, and how do you know the problem isn't caused by worn slides? Is the air screw all the way in? Have you cleaned the jet with a ~0.014" drill bit to remove any possible obstruction?

The pressed-in jet is a #25, but even if a #30 were "best" it still will be fine with a #25 although the required position of the air screw will make it more sensitive to adjustment than one might like.
 

Vincent Brake

Well Known and Active Website User
VOC Member
These Amals came with the bike in nearly brand new condition.On the other Hand Fitting mikunis on a Vincent is to my mind a Little bit like eating a wiener Schnitzel with chinese sticks.You can eat it but it doesn`t look good.Erik
Well its rides perfect Erik.
 

Little Honda

Well Known and Active Website User
VOC Member
These MK1 Concentrics have one advantage: They are the smallest carbs, re venturi diameter. Especially for
Norvins, where you cannot fit any other carb without cutting parts of the frame or rear head fins, if you want
to have your front carb sitting vertically and not touching anywhere else.
Only a week ago, I had a Mikuni flat slide carb on loan from TOPHAM Mikuni with a 32mm dia., to suit my inlets. - No chance. There are pics of a very nice NORVIN somewhere in this forum which will be offered in
an auction somewhen next year. This one does have the Mikuni TM carbs, even with air filters.
Regrettably, it cannot be seen, how the builder got them in place.
Also my experience: Very difficult to adjust MK1 Concentrics. It helps, to have vacuum dials for adjustment.
I found out, that the smoothest tick-over was achieved with a different slide position of front and rear carb,
which is probably caused by the angled centreline of the front inlet channel, if yr carb sits correctly with
unaltered frame and uncut head fins.
Moreover, they use to loosen their adjustment during a ride. They say, that the old ones with pilot jets are
better, than the later ones without.
It must be said, however, that Vince Lonsdale´s "D" runs absolutely perfect on these carbs. It can be done!
 

Attachments

Shane998

Active Website User
VOC Member
These MK1 Concentrics have one advantage: They are the smallest carbs, re venturi diameter. Especially for
Norvins, where you cannot fit any other carb without cutting parts of the frame or rear head fins, if you want
to have your front carb sitting vertically and not touching anywhere else.
Only a week ago, I had a Mikuni flat slide carb on loan from TOPHAM Mikuni with a 32mm dia., to suit my inlets. - No chance. There are pics of a very nice NORVIN somewhere in this forum which will be offered in
an auction somewhen next year. This one does have the Mikuni TM carbs, even with air filters.
Regrettably, it cannot be seen, how the builder got them in place.
Also my experience: Very difficult to adjust MK1 Concentrics. It helps, to have vacuum dials for adjustment.
I found out, that the smoothest tick-over was achieved with a different slide position of front and rear carb,
which is probably caused by the angled centreline of the front inlet channel, if yr carb sits correctly with
unaltered frame and uncut head fins.
Moreover, they use to loosen their adjustment during a ride. They say, that the old ones with pilot jets are
better, than the later ones without.
It must be said, however, that Vince Lonsdale´s "D" runs absolutely perfect on these carbs. It can be done!
Or make custom manifold like these IMG_2449.jpg
 

vibrac

Well Known and Active Website User
VOC Member
All depends on the underside of the tank 28mm mikuni fits my comet easily 34 is a bit of a problem but who wants a road bike with that orafice on today's monitored roads?
 

erik

Well Known and Active Website User
VOC Member
The mk1 are like new with new heavy brass slides from surrey cycles.The airscrew I have to Close nearly full to have a better tickover.On my comet this carb works perfect ,the engine is running like a swiss clockwork.this carb is with separate Pilot Jet!
 

Little Honda

Well Known and Active Website User
VOC Member
All depends on the underside of the tank 28mm mikuni fits my comet easily 34 is a bit of a problem but who wants a road bike with that orafice on today's monitored roads?
So true. But, on a Comet, you could also fit a supercharger without changing frame geometry...;)
 

Bill Thomas

Well Known and Active Website User
VOC Member
I was always told , That type of bell mouth, Was not good ?.
Note the racing ones only go to the big hole, The small holes are kept away from main air flow !.
Cheers Bill.
 

erik

Well Known and Active Website User
VOC Member
the bellmouthes aure not for Performance on the bike they are flame traps.
 

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