Amal needle jet size

lazyeye6

lazyeye6

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I have a 1970 Triumph Tiger (TR6R). I haven't been into the carburetor for
10 years, so I pulled it apart to clean, inspect and clear the idle circuit.
I had this a new chrome slide installed 10 years ago. It has performed
faultlessly since then. I found that it had a 106 needle jet installed and on
reviewing the service manual found that the specified needle jet is 107.
As I said, it starts easily and runs nicely with no coughing or stumbling.
The spark plugs are a darker brown than the tan color I would want, suggesting
a dry carbon buildup. So I'm thinking it may be running a bit rich. I could
adjust that with the air screw. The needle clip is on the center (2nd) notch.
I would think that the 107 jet would make it run even richer. Anyone have
any thoughts on how this carb is or should be set up?
 
lazyeye6 said:
1970 Triumph Tiger (TR6R).


I found that it had a 106 needle jet installed and on reviewing the service manual found that the specified needle jet is 107.
Click to expand...

.106 from 1970 according to the parts books.
 
Sadly not uncommon!

Factory manual for T140E models is all over the place with regards to carb settings!
 
Fast Eddie said:
Sadly not uncommon!

Factory manual for T140E models is all over the place with regards to carb settings!
Click to expand...

OK, all back together with the 106 needle jet and bike runs flawlessly. I shouldn't
need to pull the carb apart again for another 10 years when I undoubtedly will ask
the same question. :confused:
 
OK, it isn't 10 years later, but I began having trouble with the slide on my carb sticking open. So I opted to buy
my Tiger a new Mark 1 Amal. A 930. It came set up as per the specs as follows: 230 main, 106 needle jet, Std needle,
needle position: 2 (middle notch), slide: 3 1/2.

Got it dialed in and went for a test ride. It is snappy, no coughing and everything I could ask for. EXCEPT that it bogs down
on WOT and then accelerates when I let off the gas. The plugs have perfect light tan/gray color, the air filter is OEM and
clean. I had disassembled and cleaned all of the swarf out of this new-in-the-box carb before reassembly and mounting.

Common wisdom suggests I should put in a smaller sized main jet. But what size? Buy a bunch of sizes until I get it right?
Anything else I should look at?
 
I am thinking that you might be running out of gas at WOT. Possible cause could be clogged screens in fuel tap or needle seat banjo, or too small a main jet.

Slick
 
I hadn't thought that a possibility. Certainly with the precious carb with identical set up, same taps and same banjo there was no bog down at WOT.
Will try with both taps open to see if that has any effect.
 
Why not try a .107 just to see what happens. It is cheap and easy to do. A few years ago I did a top end on a single carb T140. It ran well but didn't seem to have any zip to it. A .107 made a noticeable improvement and it is running happily to this day. My theory is that fuels have changed quite a bit since 1970 and perhaps the specs should change also. It's well worth the $15 to find out.
With your bike there is the question of in town or open road. In town riding will foul spark plugs a lot sooner than open road riding so it's not a good indicator of anything.
 
seattle##gs said:
Why not try a .107 just to see what happens. It is cheap and easy to do. A few years ago I did a top end on a single carb T140. It ran well but didn't seem to have any zip to it. A .107 made a noticeable improvement and it is running happily to this day. My theory is that fuels have changed quite a bit since 1970 and perhaps the specs should change also. It's well worth the $15 to find out.
With your bike there is the question of in town or open road. In town riding will foul spark plugs a lot sooner than open road riding so it's not a good indicator of anything.
Click to expand...


Needle jet size has no effect on mixture at full throttle.
 
seattle##gs said:
Why not try a .107 just to see what happens. It is cheap and easy to do. A few years ago I did a top end on a single carb T140. It ran well but didn't seem to have any zip to it. A .107 made a noticeable improvement and it is running happily to this day. My theory is that fuels have changed quite a bit since 1970 and perhaps the specs should change also. It's well worth the $15 to find out.
With your bike there is the question of in town or open road. In town riding will foul spark plugs a lot sooner than open road riding so it's not a good indicator of anything.
Click to expand...

If your plugs foul, are you sure you’re using the right ones?

Most Bonnies (T120s and T140V) use Champion N3 or NGK 8 (or equivalent).

BUT the T140E needs hotter plugs to avoid fouling, Champion N5 or NGK 6 (or equivalent). I know from recent experience that T140V plugs will foul in my T140E and cause all sorts of running issues!

And beware, some suppliers are not even aware of this...
 
Triton Thrasher said:
Needle jet size has no effect on mixture at full throttle.
Click to expand...
The title of this thread is "Amal Needle Jet Size"

My theory is that very few people know what the main jet size should be because no one is up that high in the RPM range. 7000RPM is the limit for these motors, if you left the throttle full on and let the motor catch up to it I think it would be up in the 12000 range. No one is ever there.
 
Which jet is in play is actually dictated by the slide position.

Main jet comes in at WOT. Whether you’re doing 6,000, 7,000 or 12,000 rpm... it’s still on the main jet.
 

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