general (amal) carb question

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joe czech

joe czech

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just askin' - running a #3 throttle slide vs, a #3.5 will richen the mixture mid-range - correct??? if so, can that be offset by moving the needle clip up by one notch? which component would have a greater effect on mixture? second question - with everything being equal, what differences would one see between a .106 vs .107 needle jet??? I'M GUESSING a .107 would also richen the mixture mid range - ????
 
No, slide cutaway changes the mixture off idle on the slides initial lift ie first 1/4 of throttle travel.

Moving needle changes mixture 1/4 to 3/4 of travel.

Bigger needle jet will enrichen the 1/4 to 3/4 of throttle travel but by larger amount than moving needle.

106 v 107 is identified by stamping and the hole is bigger ie .106" vs .107"
 
If 106 is right for your bike, then 107 will be noticeably too rich. So will a worn 106.

Needle in the right notch gives you good response accelerating between 1/3 and 3/4 throttle when overtaking. If it’s running well, don’t move the needle.
 
Triton Thrasher said:
If 106 is right for your bike, then 107 will be noticeably too rich. So will a worn 106.

Needle in the right notch gives you good response accelerating between 1/3 and 3/4 throttle when overtaking. If it’s running well, don’t move the needle.
Click to expand...
really wasn't changing anything. my 74's running just fine, although i don't have anything to compare it to. running a 260 main, .106 needle jet, 3.5 throttle slide, needle p/n 928/104 w/ clip on center notch. just curious what's the impact if i went to a #3 slide.
 
The slide cutaway makes a difference to how the bike comes off idle, when you open the throttle fairly slowly, like when you’re riding in slow traffic.
 
The difference between a 0,106 and a 0,107 needle jet when using petrol as fuel, might be too large to get best acceleration up through the gears by moving the needles However if you get it better, you might find the performance of your bike becomes more dependent on the weather. Even with methanol fuel, the difference in jetting which stops a motor from being sluggish and makes it perform very well, is very small With race bikes, you can cope with that. I would run a road bike slightly rich if I used petrol. You do not really need that extra boost you get when you get the jetting really right.
 
Joe has raised a point that I have been "pondering" about for sometime- all my books & manuals state that an 850 has a 3.5 slide yet when I go to Andovers online site the 3 sections for 850's list the slide as a 3 and the only reference for a 3.5 is for a MK2A, is this a change for modern fuels? your thoughts?
 
possm said:
all my books & manuals state that an 850 has a 3.5 slide yet when I go to Andovers online site the 3 sections for 850's list the slide as a 3 and the only reference for a 3.5 is for a MK2A, is this a change for modern fuels? your thoughts?
Click to expand...

More likely another AN parts error as the 850 Amal carb kits come with 3.5 slides.

www.rgmnorton.co.uk

32MM AMAL PREMIER MK1 CONCENTRIC CARBS (MATCHED PAIR)

PACK136 RGM NORTON
www.rgmnorton.co.uk

pack136-amal-mk1-carb-set-850-commando-1973-74 - British Motorcycle Parts Ltd - Auckland NZ

www.britishmotorcycleparts.co.nz www.britishmotorcycleparts.co.nz
 
The main difference is the shape of the spray tube. The 928/104 ( 4 ID ring needle) uses the stepped spray tube # 928/107 and a 3-1/2 slide

the earlier 32mm carbs used used a 622/124 ( 2 ID ring needle) . and a tall spray tube # 622/074 and a #3 slide .

All carbs for Commandos should have material removed from the inner throttle stop boss, so they don't touch in the middle.

Normally the carbs with the stepped spray tubes need the needle clip in the top ( leanest groove) as they run a little richer as the 106 needle jet wears a little .

Stock MK3 with the oil vapor feeding into the eqilizer tube changed carb settings quite a bit.
 
new question - does compression ratio have an impact on overall carb jetting. say you have two identical engines, except for CR - one has a 9:1 and the other, a 10.5:1. my WAG is jetting, across the full throttle range would have to go more rich. right, wrong, no impact - ?????
 
joe czech said:
new question - does compression ratio have an impact on overall carb jetting. say you have two identical engines, except for CR - one has a 9:1 and the other, a 10.5:1. my WAG is jetting, across the full throttle range would have to go more rich. right, wrong, no impact - ?????
Click to expand...
....this should be good
 
Carl H said:
snipped
All carbs for Commandos should have material removed from the inner throttle stop boss, so they don't touch in the middle.
snipped
Click to expand...
Carl, do you have a photo of this mod? I'm having a hard time trying to visualize what you suggest doing.
 
I think Carl is referring to the unused casting on the carb body ( the bit below the circle). If that is not machined or filed flat the carbs won't fit. The correct carbs come with this mod already done.

Handy tip -

I have completely removed the unused tickler boss (circled) on my carbs as it makes getting at the inner nuts a lot easier.


general (amal) carb question
 
chaztuna said:
Carl, do you have a photo of this mod? I'm having a hard time trying to visualize what you suggest doing.
Click to expand...
IN the older days, when I sold carbs, My supplier listed them as 932 std and 932 Norton. Now It seems like big sellers can order them with the features ( jetting) they want. The spray tubes are either the Tall cylinders like on an old 930 or 932 carb or the stepped ones like a Mikuni or the carbs with the 4 ring ID needles, Like a MK3 has.
My Combat had the tall spray tube and the 2 ring ID needle. which I call the old style 932 type .
To tune a bike you have to do it on a warm motor and learn how to do spark plug chops with new spark plugs. To make Nortons play sweet music you have to know how to tune them.
 
cliffa said:
I think Carl is referring to the unused casting on the carb body ( the bit below the circle). If that is not machined or filed flat the carbs won't fit. The correct carbs come with this mod already done.

Handy tip -

I have completely removed the unused tickler boss (circled) on my carbs as it makes getting at the inner nuts a lot easier.


View attachment 78823

it is the It is unused Throttle stop boss, That is the part that hits, It is the boss below your circle , that protrudes out the from the bowl, You only need to remove about 1/2 of it (3/32" in the Amal carb book)
Click to expand...
 
chaztuna said:
Carl, do you have a photo of this mod? I'm having a hard time trying to visualize what you suggest doing.
Click to expand...
Look at a Norton carb any of the Commando ones, you have and look at the one in the picture that Cliffa sent. The Norton carbs have some of the Throttle stop boss removed , so the carbs don't touch in the center when they are installed.
 
cliffa said:
I think Carl is referring to the unused casting on the carb body ( the bit below the circle). If that is not machined or filed flat the carbs won't fit. The correct carbs come with this mod already done.

Handy tip -

I have completely removed the unused tickler boss (circled) on my carbs as it makes getting at the inner nuts a lot easier.


View attachment 78823
Click to expand...
Excellent idea. How much of that tickler boss do you remove? Any photos?
 
Here you go Charlie. You can also see circled where I notched the manifold so you can get a straight run on the socket screws.

general (amal) carb question
general (amal) carb question



Actually looking at them now I don't know why I didn't just cut it all off with a saw. It is all solid. Mmm, I may revisit that :eek:


Cheers,

cliffa.
 
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