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ET: Engine (Twin) Pilot jet


vibrac

Well Known and Active Website User
VOC Member
I have just seen a concentric installation where after cleaning in detail and the pilot screw set as rich as possible all air leaks in tract checked and slides sycronised (or not ) The rear cylinder only runs at tickover with a hand covering the bell mouth otherwise the front cylinder lugs the rear round. The way the rear picks up even after a prolonged lugging when the hand covers the carb suggests it's not ignition. When the throttle is opened it still is reluctant to chime in. They are difficult carbs.
 

greg brillus

Well Known and Active Website User
VOC Member
Yep, Just had the same on a Shadow where the floats would not let any fuel in........At low engine speed it would only run on one cylinder.........These were the Mk 1 1/2 concentric's with the choke lever on the sides........I had to do some odd alterations to get the levels right, when the floats were hanging down they were not lifting the needles off their seats and the fuel could not lift the needle of it's own weight........These were the large diameter alloy needles.
 

Chris Launders

Well Known and Active Website User
VOC Member
I had one where the float was fouling the chamber body before lifting the needle, it was a brass needle as well so would not lift with fuel pressure, after speaking to AMAL fitted a new stay up float and alloy needle and reset float level, they now recommend the float be level with the top of the float chamber, previously it was recommended .080 below.
 

Bill Thomas

Well Known and Active Website User
VOC Member
I have found It's tricky bending the new stay up float, You can do it and you don't get enough drop on the float To allow enough fuel in.
 

Nigel Spaxman

Well Known and Active Website User
VOC Member
I have just seen a concentric installation where after cleaning in detail and the pilot screw set as rich as possible all air leaks in tract checked and slides sycronised (or not ) The rear cylinder only runs at tickover with a hand covering the bell mouth otherwise the front cylinder lugs the rear round. The way the rear picks up even after a prolonged lugging when the hand covers the carb suggests it's not ignition. When the throttle is opened it still is reluctant to chime in. They are difficult carbs.
My Ducati did that until I figured out that the cam timing on the rear cylinder was out by 8 degrees. The rear cylinder wouldn't suck well until about 2000 RPMs. The cams are very long duration race cams (Imola) so if it is wrong it really doesn't work. I think the duration is about 340 degrees on those cams.
 

oexing

Well Known and Active Website User
VOC Member
A few months ago I had a very interesting design carb from Aliexpress, extremely low price and a kind of flat slide with round sector around the needle jet. We have not tried it yet , but you cannot be very wrong at € 30.- brand new. A set of jets is a tenner. Well, being an old fart I would not fit it onto a classic but my friend is into SR 500 racing so we got a 38 mm plus twist grip set at € 50.- . . . . .

Vic

flat slide carb

flat side carb Ali

flat slide internals
 

Bill Thomas

Well Known and Active Website User
VOC Member
It will be interesting to hear how you get on, I have seen the advert and always wondered, For that money,
How could they make it.
We made these in 1970, Didn't have enough money for Carb's !.
Just a bit of alloy tube, A rotary jet and a butterfly.
They got me to the IOM and back !.
Cheers Bill.
 

Attachments

Vincent Brake

Well Known and Active Website User
VOC Member
Now this is all better than just a mere pilotjet.....

Wonderfull thoughts all

And waiting for a mockup, mockup like them new Triumphs
.....
 

erik

Well Known and Active Website User
VOC Member
To alter the Level in the float chamber of a concentric mk1 is best done by altering the height of the valve seat in the bowl.You can press it out and Fitting different rings und it or milling the small flange more narrow.I hope you know what I mean.Erik
 

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