Carb settings.......

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JOHNO23

JOHNO23

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Gents, I’ve just started up my rebuilt mk3. It has a pW3 cam ham can air filter and straight through peashooter pipes with no balance pipe. It has new Amal premiers . Starting point for the premiers is 19 pilot ,106 needle and 260 main with a 3 1/2 slide. Not sure what setting the needle is on .Bike won’t run without the choke on. (air slides down). Suggestions please........... I thought perhaps change slide to 3, raise needle and adjust pilot in 1/4 turn or more. What settings do you guys have with a similar setup to me?
 
Mines the same with the same set up, been advised to raise the needle from the top setting to the middle. Not done it yet as away on holiday till next week.
If you beat me to itlet me know how you get on.
Mine was lacking in mid range till I opened the choke and away it went.
 
Pilot 1 and a bit turns out, synchronised by removing float bowls and jet and watching needles raise together, carb slides on the stops. You will need to set it up again I'm sure.
 
JOHNO23 said:
Gents, I’ve just started up my rebuilt mk3. It has a pW3 cam ham can air filter and straight through peashooter pipes with no balance pipe. It has new Amal premiers . Starting point for the premiers is 19 pilot ,106 needle and 260 main with a 3 1/2 slide. Not sure what setting the needle is on .Bike won’t run without the choke on. (air slides down). Suggestions please........... I thought perhaps change slide to 3, raise needle and adjust pilot in 1/4 turn or more. What settings do you guys have with a similar setup to me?
Click to expand...
I assume you mean it won't run without the choke even when it is warmed up.

You have got exactly my setup on my 850 Mk11. Peashooters hamcan air filter and the same carb set up.

And my bike is rough on startup but fine once warm.

I'd have a look at float height first. Did you clean the air passages on the new carbs. Swarf blocking the passages is unfortunately pretty common
 
Yes lowered the slides, in it's initial stage I had good pick up to around 20mph then nothing just a flat spot, full throttle and it was away. Somebody told me to apply the choke while riding it and that did the trick.
So the needle needs to be set 1 notch lower so I am told.
 
Ratboiler said:
Yes lowered the slides, in it's initial stage I had good pick up to around 20mph then nothing just a flat spot, full throttle and it was away. Somebody told me to apply the choke while riding it and that did the trick.
So the needle needs to be set 1 notch lower so I am told.
Click to expand...
Do the cheap easy things first. Lift the needles, richen the air screws a tad, to help out weak slides, check the float heights, though I don't think that is the issue as the motor runs well on full throttle.
Dave
 
johnm said:
I assume you mean it won't run without the choke even when it is warmed up.

You have got exactly my setup on my 850 Mk11. Peashooters hamcan air filter and the same carb set up.

And my bike is rough on startup but fine once warm.

I'd have a look at float height first. Did you clean the air passages on the new carbs. Swarf blocking the passages is unfortunately pretty common
Click to expand...
Even when warm it struggles to keep going without choke.....
Float height was fine I did blow out passages before fitting them......
 
Hi John,
I went through a lot of grief putting new Premiers on my MKIII. Checked everything three times. One carb just would not stop fouling the plug in 30 seconds. Cold pipe on that side. Finally took an old bowl and float and put it on the new Premier. Voila! The weird thing was that on my fuel level jig, the new Prem bowl and float measured OK. I also had to run the needles in the middle clip positon to get midrange back to normal . So if you get stumped, and have an old set of Amals --try different bowls. BTW , "amal" in Arabic means hope. We live in hopeful anticipation that someday our Amals will actually run right.
Cheers,
Kara
PS, did you put your balance tube back on ?
 
Talked to an engineering friend. He fitted new Premiers to a Trident.

Two worked fine and one was hopeless. Would either starve or totally flood.

He finally discovered the tags on thecstayup float were not sliding smoothly around the needle. The ones circles in the attached photo. He gently opened up the slot and got the float needle moving smoothly. He was also very careful with the bowl gasket fit because that can also catch the float.

He said the tags looked just fine but did not work smoothly. After gently filing the slot the carb finally worked.

This experience might explain the cure that Kara found when substituting a different bowl and float.
My friend has found the Premier carbs can definitely need a bit of fettling sometimes.
 

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I did the same in the end, and changed over the old float for the new that sorted the float height, but not the mid range, so the needle position is next on the list.
The problem I had was the float shutting off early, so bent the tang to correct the height. All was fine for about a minute then it started to flood. Checked the gasket, and float and all was ok, started the bike and the float was sticking for some reason.
 
Johnm's brilliant comment might be the explanation ! My troubled Premier actually measured fine on my bench test fuel level jig, but ran extremely rich on the bike to the point of non functioning. Sooted the plug in 30 seconds. Perhaps after riding season, I will do some experiments with the Premier bowl and float again... I recently found out the "amal" means hope in Arabic. We offer money on the altar of the Carburetter Gods and hope that someday our Amals will function correctly.
 
Yes my friend is not a huge fan of the stay up floats. The idea is good but sometimes they give problems for no obvious reason. They look perfectly fine but jam either up or down in practice.

He gently opens up the slot with a file and polishes the surface and then they can be made to work

Incidently he was the same guy who told me about the problems with the Mk1 carb bodies. When he worked for British spares in Wellington they sold literally hundreds of carbs. And had a box of about 5 or 10 returns that could not be tuned. When he sawed them in half most showed porosity around the internal passages.

He is originally a post office tech by training so is good with circuits but for the past 20 plus years he has basically repaired and rebuilt engines, gearboxes suspension etc. Vincent's, Velos, Triumphs, Harleys, BMW, Norton's, BSAs. Lots of very old stuff back into the 1920s.

These days he is trying to retire and only does work for old customers keeping a low profile
 
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An update......... It wasn’t the carbs! I called Norman White today to check what he would recommend as the settings for my carbs. I bought premire’s for an 850mk3 with the only difference from std being they had 260 mains. I set the Boyer as per instructions statically and got the bike started but it wouldn’t run without the choke on .
Norman told me those carbs would be fine as they were,and not to change anything,plus the only issues he ever gets with the new premiers is sometimes the float height caused by something to do with the float needle and how it fits with the float........( not sure exactly) but easily sorted.He said don’t touch the carbs until you have the timing set.
I then switched my attention back to the timing.................to cut a long story short setting the magnetic rotor plate in line with the “Norton” logo on the timing case whilst engine is at 31 degrees btdc did not even get close to where it should be! The bike started but as I have said wouldn’t run without choke.I managed to improve it slightly at the extreme of the adjustment available on the stater plate, so then had to reset the rotor to compensate.I did this a couple of times.I set the rotor from the instructed 9 o’clock/ 3 o’clock position to 8.00 o’clock/ 2 o’clock position then strobed it. The bike ran much better but the timing mark was still not in sight!! I could just see it to the left. I reset the rotor again and was then able to strobe and set to 31 degrees btdc. Bike ran great and ticked over and picked up beautifully.I still need to tweak the tick over with the pilot screws but nothing more. I was amazed how far I had to move the rotor to get the static timing to a point where the engine would run reasonably well or at least well enough to strobe it. I was also amazed how the engine ran when the timing was so far out! The Boyer instructions are a mystery to me.........:oops:
 
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JOHNO23 said:
An update......... It wasn’t the carbs! I called Norman White today to check what he would recommend as the settings for my carbs. I bought premire’s for an 850mk3 with the only difference from std being they had 260 mains. I set the Boyer as per instructions statically and got the bike started but it wouldn’t run without the choke on .
Norman told me those carbs would be fine as they were,and not to change anything,plus the only issues he ever gets with the new premiers is sometimes the float height caused by something to do with the float needle and how it fits with the float........( not sure exactly) but easily sorted.He said don’t touch the carbs until you have the timing set.
I then switched my attention back to the timing.................to cut a long story short setting the magnetic rotor plate in line with the “Norton” logo on the timing case whilst engine is at 31 degrees btdc did not even get close to where it should be! The bike started but as I have said wouldn’t run without choke.I managed to improve it slightly at the extreme of the adjustment available on the stater plate, so then had to reset the rotor to compensate.I did this a couple of times.I set the rotor from the instructed 9 o’clock/ 3 o’clock position to 8.00 o’clock/ 2 o’clock position then strobed it. The bike ran much better but the timing mark was still not in sight!! I could just see it to the left. I reset the rotor again and was then able to strobe and set to 31 degrees btdc. Bike ran great and ticked over and picked up beautifully.I still need to tweak the tick over with the pilot screws but nothing more. I was amazed how far I had to move the rotor to get the static timing to a point where the engine would run reasonably well or at least well enough to strobe it. I was also amazed how the engine ran when the timing was so far out! The Boyer instructions are a mystery to me.........:oops:
Click to expand...

Have you verified the scale in the cover with a timing disc?

If not, do so before proceeding any further.
 
JOHNO23 said:
The Boyer instructions are a mystery to me........
Click to expand...

But did you follow the Boyer instructions?


JOHNO23 said:
to cut a long story short setting the magnetic rotor plate in line with the “Norton” logo on the timing case whilst engine is at 31 degrees btdc did not even get close to where it should be!
Click to expand...

After positioning the rotor (best not fully tightened) did you then check the magnet was visible in the upper timing hole with the stator plate set halfway along its slots as it says in the instructions that the rotor may have to be repositioned to achieve it?

"8) The magnet on one side of the rotor should now be in the centre of the top timing hole in the stator plate; this should also set it half way along its adjustment slots. If not, move the rotor until this is achieved without turning the engine from 31deg. B.T.D.C."


It would seem the instructions to...

"23) Start engine and time with a stroboscope to 31 B.T.D.C (28 DEG. with standard ignition) with the engine running up to 5000 r.p.m. This is done by moving the ignition stator plate. If the timing is not obtainable before the end of the adjustment, the magnetic rotor will have to be slackened off and moved a small amount until the correct timing can be obtained."

...perhaps wasn't followed until later (due to the perceived carb problem) where it again states the rotor may have to be repositioned in which case the timing error would have been identified that much sooner.
 
Interesting. What Norman White said matches what my friend in Wellington NZ found

"" Norman told me those carbs would be fine as they were,and not to change anything,plus the only issues he ever gets with the new premiers is sometimes the float height caused by something to do with the float needle and how it fits with the float........( not sure exactly) but easily sorted. ""

You should check the timing scale in the primary cover as suggested above.

But with respect if you find the Boyer instructions confusing it might be a good idea to contact the local NOC and see if you can find someone to guide you through the process.

Doing on line is probably going to confuse things more.
 
johnm said:
Yes my friend is not a huge fan of the stay up floats. The idea is good but sometimes they give problems for no obvious reason. They look perfectly fine but jam either up or down in practice.

He gently opens up the slot with a file and polishes the surface and then they can be made to work

Incidently he was the same guy who told me about the problems with the Mk1 carb bodies. When he worked for British spares in Wellington they sold literally hundreds of carbs. And had a box of about 5 or 10 returns that could not be tuned. When he sawed them in half most showed porosity around the internal passages.

He is originally a post office tech by training so is good with circuits but for the past 20 plus years he has basically repaired and rebuilt engines, gearboxes suspension etc. Vincent's, Velos, Triumphs, Harleys, BMW, Norton's, BSAs. Lots of very old stuff back into the 1920s.

These days he is trying to retire and only does work for old customers keeping a low profile
Click to expand...

They look like the metal tab is a stamped piece. On the upper lip opening you can see the white line on the edged which is classic rounding of the punch press sheared edge.
The while line is the concentrated reflection from rounded edge and on the other side is a ragged ass edge like a microscopic razor blade/hack saw blade. It can then grab the round step of the needle and not allow sliding. I use a 12 ton punch press making a part for my starter out of 16g stainless. so for over ten years I have to examine the results.
I can easily see why the dressing deburring can stop the problem.
JohnM
you have a good guy there!
and Thanx for the pix
Sounds like a AMAL- AH HA moment....... probably see this again until they start batch/tumble deburr these things
 
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