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Need help with Amal carbs #773049
05/08/19 6:58 pm
05/08/19 6:58 pm
Joined: Aug 2018
Posts: 37
Tualatin
J
johnpl Offline OP
BritBike Forum member
johnpl  Offline OP
BritBike Forum member
J

Joined: Aug 2018
Posts: 37
Tualatin
I am the owner of a 1966 T 120. I just recently got the old boy running again but I am having a problem with my lack of knowledge when it comes to tuning. I can only go about 50-100 miles and my new spark plugs are a dark sooty black. I remove and clean them only to have the same problem reoccur. I am currently using NGK B7ES. Seems to be running rich. Is this adjustment controlled by moving the needle on the slide? Any suggestions would be great,

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Re: Need help with Amal carbs [Re: johnpl] #773051
05/08/19 7:14 pm
05/08/19 7:14 pm
Joined: Dec 2013
Posts: 4,987
ohio, usa
kevin roberts Offline

DOPE
kevin roberts  Offline

DOPE

Joined: Dec 2013
Posts: 4,987
ohio, usa
B7ESs are a bit hot, in my experience. i use B8ES. but that shouldn't be the problem. put a timing light on the spark plug wires, doesn't matter about timing, just watch the flash to see if it's sparking more or less reliably. if it is, then look at the carbs to see whether it's too rich.

you can adjust the mixture in several place on the carb-- idle screw setting, needle position, needle jet, needle, and main jet.

the 63-70 workshop manual says this:

[Linked Image]

is this what you're running?

how old are the needle jets? if they're not new, throw them out. i'd get new needles too.



every day you do not take a chance is a day of your life that you will never get back.
Re: Need help with Amal carbs [Re: johnpl] #773094
05/09/19 1:04 am
05/09/19 1:04 am
Joined: Feb 2008
Posts: 4,866
New Jersey USA
Tridentman Offline

BritBike Forum member
Tridentman  Offline

BritBike Forum member

Joined: Feb 2008
Posts: 4,866
New Jersey USA
Do you have chokes fitted?
If so--after warming up---is the choke lever in a cable taut condition?

Re: Need help with Amal carbs [Re: johnpl] #773106
05/09/19 3:34 am
05/09/19 3:34 am
Joined: Aug 2001
Posts: 4,757
Owego, NY, USA
Mark Z Offline
BritBike Forum member
Mark Z  Offline
BritBike Forum member

Joined: Aug 2001
Posts: 4,757
Owego, NY, USA
Under normal riding, let's say, 1/4-3/4 throttle, your mixture is primarily controlled by the needle and needle jet, as you surmised. You should see what you have in there and which notch the needle clip is in, and compare with the factory settings.

If it's not something else, like ignition or choke setting, you could try dropping the needle a notch. Note also that needles and needle jets wear after many miles of use, causing an over-rich mixture, and may need to be replaced.

One way to isolate the idle mixture is to: 1. Start and warm up the engine, so that it can be restarted without choking or tickling. 2. Change out spark plugs for brand new ones. 3. Restart the engine and let it idle for a few minutes without touching the throttle. 4. Remove and look at the spark plugs. Idle mixture is controlled by the pilot jet size (if yours is removable) and air mixture screw.

Once having the idle mixture sorted, then look at plugs after a ride. If you have a place to do this, as you're cruising along, pull in the clutch, kill the ignition, and coast to a stop. If not, then just pull in as usual and don't let it idle long before killing the engine.




Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: Need help with Amal carbs [Re: Mark Z] #773200
05/10/19 12:25 am
05/10/19 12:25 am
Joined: Aug 2018
Posts: 37
Tualatin
J
johnpl Offline OP
BritBike Forum member
johnpl  Offline OP
BritBike Forum member
J

Joined: Aug 2018
Posts: 37
Tualatin
Sounds like a good plan. I do not have a choke on this bike. Any idea where the factory setting for the needle would be located (which notch), # 3 as listed above on this post?
As a follow up, I have not changed or replaced any parts except gaskets on these old amals. If I pull them off what parts would you recommend I replace?

Re: Need help with Amal carbs [Re: johnpl] #773204
05/10/19 3:00 am
05/10/19 3:00 am
Joined: Aug 2001
Posts: 4,757
Owego, NY, USA
Mark Z Offline
BritBike Forum member
Mark Z  Offline
BritBike Forum member

Joined: Aug 2001
Posts: 4,757
Owego, NY, USA
Originally Posted by johnpl
Sounds like a good plan. I do not have a choke on this bike. Any idea where the factory setting for the needle would be located (which notch), # 3 as listed above on this post?
As a follow up, I have not changed or replaced any parts except gaskets on these old amals. If I pull them off what parts would you recommend I replace?


The factory settings are as listed above by Kevin. Do you have Monoblocs or Concentrics? If Concentrics, the needle position is "2".

In general, carburetor parts other than gaskets and O-rings are not replaced unless there's a problem. Needle and needle jet wear depends on mileage. You can replace them out of hand if you like, but they might not need it.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: Need help with Amal carbs [Re: johnpl] #773219
05/10/19 8:14 am
05/10/19 8:14 am
Joined: May 2007
Posts: 2,244
Christchurch NZ
R Moulding Online content
BritBike Forum member
R Moulding  Online Content
BritBike Forum member

Joined: May 2007
Posts: 2,244
Christchurch NZ

Somethings to bare in mind. For starters your bike should be equipped with Monoblocs. If it has Concentrics fitted the factory setting will be different. Also if your bike is actually a 66 T120 it will be fitted with 389-203 carbs, these are inch and an eighth. If however it is a T120R supplied to JOMO it will be fitted with 389-95 carbs, these are inch and three sixteenths.

The only jet that tends to show signs of wear is the needle jet, this is recommended to be replaced every 12000 miles. Start with the needle jet.

Rod


So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth;
And pray that there's intelligent life somewhere out in space,
'Cause there's bugger all down here on Earth!
Re: Need help with Amal carbs [Re: johnpl] #773221
05/10/19 8:46 am
05/10/19 8:46 am
Joined: Aug 2001
Posts: 4,599
argyll. scotland, uk
gavin eisler Offline
BritBike Forum member
gavin eisler  Offline
BritBike Forum member

Joined: Aug 2001
Posts: 4,599
argyll. scotland, uk
Sooty plugs and old AMAL Monoblocs.

Check in the float bowls.
Three good possibilities.
Punctured floats, remove and check .
Missing float spindle spacers, floats are held in position by a short brass collar which fits over the shafts.
Easy to leave out.
Poorly seated float needle valves, remove needle valves and replace with Al viton tipped type.

look at the fuel feed banjo unions, these should NOT have a fiber washer between union and carb body, ( modern repops do have this , but if fitted to old bodies causes over rich high fuel level), an easy mistake to make.

If all this checks out ok start looking at pilot air screw settings and needle clip heights.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Need help with Amal carbs [Re: johnpl] #773235
05/10/19 11:20 am
05/10/19 11:20 am
Joined: Aug 2012
Posts: 730
West Virginia, United States
Beach Offline

BritBike Forum member
Beach  Offline

BritBike Forum member

Joined: Aug 2012
Posts: 730
West Virginia, United States
Needle jet and needle as stated before. The jet can wear to a larger size causing a rich condition.


Bill
1974 Norton Commando
1966 Lightning
1965 Lightning Rocket
1966 Norton Atlas
1967 Norton Atlas
1948 Panhead

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