new carbs questions

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alan hodge

alan hodge

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well, boys, i bought two new amule carbs.....932 /42 and 932/43....jetted 106 needle jet....260 main .....3.5 slides....pilot unknown....four rings....moved needle clip from 1st groove as supplied to middle groove..this on '73 850 motor....conical 'pod' air 'cleaners' non-balanced piped peeshooters with louvers inside.........ok so after the usual fettling/cursing got them on ....turned air screws out 1 1/2 turns....bike started first kick after moderate amount o ticklin' hhhmm.....spitting back and backfiring in exhaust upon first 12 mile jaunt......took little screwdriver with me and stopped every cuppla miles and screwed air screw in a bit til got smooth idle......bike ran great no flat spots ,,,,,overall was much smoother than single mikuni and pulled and pulled...........when i got home i let cool off...plugs dark ..AIR JET WAS ONLY TURNED OUT 1/2 TURN far from textbook 1 1/2 turn whaddy think? seat o pants o textbook?
 
My original 932's run perfect with the air screw about 3/4 with an occasional spit and plugs stay good there. Any more or less = bad things, so no jacking with it. I think I run top ring but carbs are ancient too.
 
alan hodge said:
i bought two new amule carbs.....932 /42 and 932/43.
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Did you specifically order 932/42 and /43 or were they just what you were sent as I wouldn't expect 932/42 & /43 to have 260 main jets?
The standard carbs for an 850 Mk1 would be 932/29 and /30.

alan hodge said:
pilot unknown.
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Assuming they are standard Amals and not Premiers then the pilot bush is a 'fixed' (0.016") jet.

alan hodge said:
AIR JET WAS ONLY TURNED OUT 1/2 TURN far from textbook 1 1/2 turn whaddy think?
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1 1/2 turns is the basic starting point although you could check if the fuel (not float) levels are set correctly.
amalcarb.co.uk

Optimising Amal Mark 1 Concentric Fuel Levels | AMAL Carburetters

The Optimising Amal Mark 1 Concentric Fuel Levels page for the AMAL Carburetters website.
amalcarb.co.uk amalcarb.co.uk
 
they were what was sent float levels ok main jets as marked on box were 220 i asked for 260s as i read that is what is for that year i have a pair of 220s in shed
 
alan hodge said:
they were what was sent float levels ok main jets as marked on box were 220 i asked for 260s as i read that is what is for that year i have a pair of 220s in shed
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That's ok then.
 
260s OK? or 220s? just curious about why only 1/2 turn out plugs (champion N4G) as dark as single mikuni was but bike runs very well/smooth
 
perhaps you still have #17 pilots in place. Almost impossible to get to know that they're on.
 
not premeers but have adjustable stay up floats and viton tipped float needles and removeable plug on opposite side of carb from air screw label on box sez...L932N 32mm Norton 850 bush pilot jet NJet 106 ....valve 3.5
 
If you are going to leave it at 1/2 turn out, run a hotter plug if you want to see a lighter plug color.

The fact that a pair of 32mm Amals worked better than a single 34mm Mikuni is to be expected. A pair of 34mm Mikuni carburetors would work better than 1 as well. But they look aesthetically wrong on a Commando sticking out past the side of the tank. Amals are a good compromise. 1/2 a turn and dark plugs is worth more investigation in my book, but I'm not rocking the boat.

If'n it were me, I'd drop the needle clip down a notch and raise the needle, or use a needle shim under the current position to see if it helps. That might get you in the 3/4 turn range. Everything makes a difference. And it sort of sounds like you are tuning the off idle to 1/4 throttle with the air screw, which can be tuned with clip position. But I don't know the secret handshake, so ignore as appropriate.
 
they came out of box with clip in top groove i put it in middle one am chasing that tan color on plugs am running 90 octane non ethanol as i said bike is a lot smoother running/sounding almost turbine-like
 
The black plug colour, was that from doing a throttle chop after running at speed, large throttle opening or just from idling or less than 1/4 throttle opening run?

I've always heard that only a proper throttle chop type run can tell you much meaningful info from plug colour, esp with modern fuels.
 
running 50mph two miles then pulling into driveway and cutting off bike asap....the search for the Waffle House waffle golden brown holy grail sparkling plug color
 
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Why are you running N4s? Should be N7s shouldn’t they?

Sounds to me like they just might not be getting hot enough to burn clean?

When checking plugs like you are, the speed is irrelevant, it’s the throttle position which is the key, as that dictates which parts of the carb are in play. I’d guess that at 50mph you’re only on a quarter throttle, at which its the slide cutaway and needle jet doing most of the metering.

A good tip is to mark the twistgrip at: closed, 1/4, 1/2, 3/4, WOT. You can then tell at a glance which part of the carb circuitry you’re using.
 
i ride low and slow at 50mph throttle is barely cracked i dont think N4G (Gold palladium) and N7 are in same category
 
alan hodge said:
i ride low and slow at 50mph throttle is barely cracked i dont think N4G (Gold palladium) and N7 are in same category
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In that case you’re on the pilot and slide cutaway. I’d venture that you might have the air screw wound in so far to richen it up and compensate for the slide cutaway. 3.5 sounds a bit weak to me for an 850 with pod filters etc.

Don‘t know nowt about palladium. But as you ain’t loading the engine hard etc, I would suggest putting in standard plugs whilst you fine tune the carbs, get a solid baseline, and then experiment with posh plugs.
 
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