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Discussion Starter · #1 ·
Got the bike running better now, thanks to everyone’s help.. so been out on it tonight and have another small issue.

When it’s hot (after about 2 miles), it can miss on opening the throttle (just of closed position). Does not do it when under load.. you let off and wind back on again, it’s okay... It does it when you’re going downhill on over-run, then you slightly open up... just one miss then off... Or if you’re at tick over.., just one miss and off.... or over-run on the flat... just a miss then off....?

Any thoughts?... got a Boyer fitter... could it be the bits getting warm... pulls like a train otherwise and Amal MK2’s... could it be air screw (1.5 turns out).. or some other jetting issue?
cheers :smile2:
 

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1.5 turns is not a recommended setting: it is a starting point.

Your mixture is either too rich or too weak at a small throttle opening. If you can't tune out the hesitation by altering the pilot screw position, you may need a different slide cutaway.
 

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If all else is well, on twin carb bikes that is a classic symptom of carb slides not synchronised.
 

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Discussion Starter · #4 ·
thanks all... I'd guess its too weak then?... will try pull em out a tad...
will also remove, clean, take off tickover and ensure they both work together... see what happens :) cheers
 

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Discussion Starter · #6 ·
Yes it could be bad synch of twin carbs, or even the ignition.

Screwing the mixture screw in is enriching.

If richer makes it worse, you know what to try next...
Runs a lot better at 2 turns out... so running rich... so took the carbs in bits and the needle was on the second notch up... so raising the needle... Should it be on 3 or even 4? (US spec so 200 mains)

also, the main jet tube into the intake track are differant heights?.. look like the original carb (lower one) and a newer carb (high one)... about 2mm and 4-5mm... do you think this will make any odds?
 

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Needle position should be set for healthy pulling, with no lumpy running or plug fouling, at 1/3-2/3 throttle. Your problem is not likely to be needle position.

As for your odd mixture of parts, I think photos are required.

On Mk 1 Amals, the needle jet wears fast, causing richness at small throttle openings and must be renewed. I don't know if it's the same on Mk 2 carbs.
 

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Discussion Starter · #8 ·
Needle position should be set for healthy pulling, with no lumpy running or plug fouling, at 1/3-2/3 throttle. Your problem is not likely to be needle position.

As for your odd mixture of parts, I think photos are required.

On Mk 1 Amals, the needle jet wears fast, causing richness at small throttle openings and must be renewed. I don't know if it's the same on Mk 2 carbs.
For some reason it wont let my add a pic?... Anyway.. problem solved with the tube... 2 hours with a swiss file last night and they are both exactly the same size now... got to help....
The needle if counting from the top is in position 4.. so pulling the needle up... from the Haynes it says it should be in position 2... so will move it to position 3 see how we go... Also the air screw should be 2 1/2 turns out and not 1 1/2 as I was told before.. .so even more to go... will bob it all back together when my new float chamber gaskett arrives with new filters and a seal to the box.. and see what happens... :)
 

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Discussion Starter · #9 ·
Here we go... if you look, you can see the LHS tube is a good 2.5mm taller than the RHS one... (RHS being the original carb)... otherwise everything is the same :)
 

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Discussion Starter · #11 ·
Make sure the needles and needle jets are identical too.

Are both spray tubes (also called emulsion tubes, the thing you filed) pressed fully up into the casting?
Yes.. pushed fully home... there is a cross drilling comes in from the front.. on one tube it goes through the skirt of the tube. on the other the tube is above the cross drilling.. so totaly differant parts (internaly measures the same as it necks down at a given point).... Also the needles.. same number 2A1.. and both have 5 steps.. but the spacing between the groves is bigger on one than the other...
And there's more.... Measuring the slider seat where the neddle clip sits (and therefore the needle position) relative to the top of the needle jet... one slider needs 0.5mm off the seat to get them both the same....
Same carb... but with slight differances...
Not sure 0.5mm would make that much differance in the real world but may as well get them knob on.

It's a US spec... jets are:-
cold start 25
main 200
neddle jet 105
needle 2A1

any idea if that correct?
 

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You do need identical carbs.

Any difference at all between needles, needle jets, drillings, clip notches, or any such thing is bound to make the bike untuneable.
 

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The original jetting used by Triumph to pass the EPA testing was:

124/026 #25 pilot jet
124/026 #50 choke jet
2928/031 105 stainless cross drilled (.035" hole) needle jet
2928/060 #3 slide
2928/030 2C3 needle (3 clip grooves)

The stainless needle jet was used because the brass would wear out of specification before the EPA test was finished.

The none EPA jetting is typically:
124/026 #15 pilot jet (some people go to #20)
124/026 #35 choke jet
2928/122 106 brass crossed drilled (.035" hole) needle jet
2928/060 # 3 1/2 slide
2622/124 2A1 needle (5 clip grooves - as pictured in your photo on the left)

The 2A1 needle should be used with the 2928/122 106 needle jet.
The 2C3 needle should be used with the 2928/031 105 stainless needle jet.
 

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Discussion Starter · #19 ·
The original jetting used by Triumph to pass the EPA testing was:

124/026 #25 pilot jet
124/026 #50 choke jet
2928/031 105 stainless cross drilled (.035" hole) needle jet
2928/060 #3 slide
2928/030 2C3 needle (3 clip grooves)

The stainless needle jet was used because the brass would wear out of specification before the EPA test was finished.

The none EPA jetting is typically:
124/026 #15 pilot jet (some people go to #20)
124/026 #35 choke jet
2928/122 106 brass crossed drilled (.035" hole) needle jet
2928/060 # 3 1/2 slide
2622/124 2A1 needle (5 clip grooves - as pictured in your photo on the left)

The 2A1 needle should be used with the 2928/122 106 needle jet.
The 2C3 needle should be used with the 2928/031 105 stainless needle jet.
Thanks for that... wonder if a worn out 105 becomes a 106 to go with my 2A1 pins :wink2: will see how it runs now before changing anything else... Cheers....
 
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