Advice on Amal settings for ‘74 850 please

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Back to the carbs: I must ask 'what sort of fuel are you using'? This may matter or it may not but I would consider it.
 
This is a very useful thread to me today. I've been having tuning troubles with an Atlas built with commando, 9:1 no-id head, Atlas cam with the early commando/Atlas silencers. It's been running rich on the right side to the point of fouling the BP7S plug. The conversation about welded-in baffles got me to thinking: which side was it that I bought a new silencer for? I still had the old one. Went out with a broom handle and found that the side that's been running rich has the baffle and the one that's lean/clean has had the baffle cut out. Dug through the boxes for the old silencer and found, as luck would have it, it was the correct side and had the baffle cut out. It's now shined up and on the bike and ready to test. Temp today is about 90F.
FWIW specs for this 750 motor are:

Carbs= 930 L & R
Slide=3-1/2
Needle jet =106
Needle= 2 ID rings
Pilot jet=20 (pre-68 carb)
Main jet = 220
Air cleaner= original Atlas with foam element
Silencers= Atlas/ early Commando (end of baffles cut out)
Pipes=1-5/8"
Altitude= 2500'
Attitude= good
 
not sure where we're at on this thread, but on my 74 Mk2 w/ 932's -- 260 main, 106 needle, 3-1/2 slide, (factory) pilot 25, middle position on the clip. OE air cleaner w/ standard element and original factory exhaust. easy starts and seems to run just fine, plug readings look good. we're pretty much at sea level here in palm coast florida.
 
Update on Atlas road test with de-baffled muffler in post #42: Over rich problem is gone! Both plugs look the same, i.e. too lean. So, mufflers can make a big difference.

My 850 MKIII has combat cam, Ham Can air filter, Pea Shooters, blaance tube, 932 carbs, 3 1/2 cutaway, 106 needle jets, cut-away spray tubes, 4-ring needles on center notch, 260 main jets, Boyer ign. and blue pipes.

Bluing occurred on last long trip (1000 miles) after new needle jets and needles. I believe I replaced both with the same as was there before. This was before the days of ethanol gas. Gas mileage was in the high 50s running 60-70 mph.
 
""Normally I just change all fuel and electronic changes from my phone. "

WOW, the time warp you accidentally entered has shafted you big time. :eek: If possible, find a way to go back before it's too late!!!o_O
 
""Normally I just change all fuel and electronic changes from my phone. "

WOW, the time warp you accidentally entered has shafted you big time. :eek: If possible, find a way to go back before it's too late!!!o_O
I was just stating that over the last 20 years riding I’ve always used Tune ecu whether by laptop or phone to make most adjustments on my bikes( they’ve all been Triumphs). You would just enter a new fuel map and go about your business. So I have little to no experience with carb tuning.
 
Has anybody tried #3 slides in a 850 carb running 4 ring needles, cut away spray tube, 106 needle jets etc i.e. were the 3 1/2 slides used just to meet emissions? and would #3 be an improvement?
 
Wot Wot wot , The Time Travel Aspect . Allways thought this showed the regard someone held them in . if not the general british press .

Advice on Amal settings for ‘74 850 please


Any Shop shouldve had all the Carb Componentry 'To Hand 'back then , as it was current tech . In fact they were useless if the hadnt .

One assumes this is a Tokyo or similar service center . A Tardis would be rather usefull for accessing New Norton Componentry .
Wonder if it used Lucas Electrics ? would explain the occasional sparks & smoke from the control boards . :)
 
Has anybody tried #3 slides in a 850 carb running 4 ring needles, cut away spray tube, 106 needle jets etc i.e. were the 3 1/2 slides used just to meet emissions? and would #3 be an improvement?
I have tried 3 slides with the set up you describe. Using NZ 95 gas and the 19 pilot, 260 mains. Peashooter mufflers. 1974 850. Premier carbs

I was trying to cure severe hesitation coming off idle in the 1100 to 2500 rpm range.

In the end I cured the problem by

- ultrasonic cleaning of carbs and blowing out of all passages
- correcting fuel level on one carb
- and very importantly polishing the rough edges of the stamped out tags on the premier carb floats. These tags can catch on the fuel needle and either flood or starve the carb. This problem has been reported by Norman White and independently identified by an engineer friend of mine.

After I did these 3 things I went back to a 3.5 slide and bike has run very well ever since.
 
- and very importantly polishing the rough edges of the stamped out tags on the premier carb floats. These tags can catch on the fuel needle and either flood or starve the carb. This problem has been reported by Norman White and independently identified by an engineer friend of mine.
Good point, I found the same and can easily imagine it causing very annoying and intermittent issues.
 
I find the original plastic float design to be superior to the foam premier floats. TBF, the premier foam floats allow much easier float level adjustment. OTOH, once the float level is set on the old style floats, I have never seen it change. Frankly, for several reasons I consider the foam floats of the premiers a 'downgrade' though overall the premiers are a substantial upgrade over the original Amals.
 
I had a problem with the new float sticking as soon as I tightened the bowl. Much frustration. Turned out to be the spindle the float sits on. It had a small nodule at one end of the shaft. It looked deliberate, couldn't see why it would be there. I filed it off and it's worked fine since. Amal replacement parts need checking over.
 
johnm, thanks for your reply I have always understood that 3 1/2 was the correct slide for an 850 [I am on my 4th a Mk3] I have just been on Andovers website and for 850's including the Mk3 they list #3 slides though a 3 1/2 is listed for a Mk2A im interested in your thoughts? what part of the country are you in? I'm in Christchurch.
 
I have just been on Andovers website and for 850's including the Mk3 they list #3 slides...

AN have it wrong then as 3 1/2 is the standard slide for all 850s including Mk3.

though a 3 1/2 is listed for a Mk2A

Mk2A and Mk3 have the same specification carbs (932/33 and 932/34) and that includes the slides.

"CARB PAIR - AMAL PREMIER 32MM (850 MK2A/Mk3) 220 JET"
 
johnm, thanks for your reply I have always understood that 3 1/2 was the correct slide for an 850 [I am on my 4th a Mk3] I have just been on Andovers website and for 850's including the Mk3 they list #3 slides though a 3 1/2 is listed for a Mk2A im interested in your thoughts? what part of the country are you in? I'm in Christchurch.
Yes. All my manuals say 3.5 standard.

I'm in the Wairarapa.
 
All I was asking was did the consensus feel, was the change to #3.5 due to emission consequents i.e. would performance increase excluding emissions be gained by going back to the #3 slide?
 
All I was asking was did the consensus feel, was the change to #3.5 due to emission consequents i.e. would performance increase excluding emissions be gained by going back to the #3 slide?

That will most likely vary from bike to bike, but IMHO a Commando that has been liberated somewhat with peashooters etc is probably gonna prefer #3s.
 
All I was asking was did the consensus feel, was the change to #3.5 due to emission consequents i.e. would performance increase excluding emissions be gained by going back to the #3 slide?
Johnm answered it in post 49.
Not so sure emissions were a concern at the time.

Interesting Q about the 3 vs 3.5 though.
Our fuel is not the same as when when our dinosauers were created.
With the all the additives, especially ethanol, whether it be 5% , 10%, 15% or whatever, it would seem the fuel is getting leaner and thus may require
some richer mods to our antiquated, carb power beasts.

johnm's works fine on his NZ 95, is it the same as our California gas? I'm reasonalby sure it isn't. Here, we have two blends, Summer and Winter.
Be interesting if others have tried it, and where.
I may at some point, right now got too many others items to deal with.
 
Johnm answered it in post 49.
Not so sure emissions were a concern at the time.

Interesting Q about the 3 vs 3.5 though.
Our fuel is not the same as when when our dinosauers were created.
With the all the additives, especially ethanol, whether it be 5% , 10%, 15% or whatever, it would seem the fuel is getting leaner and thus may require
some richer mods to our antiquated, carb power beasts.

johnm's works fine on his NZ 95, is it the same as our California gas? I'm reasonalby sure it isn't. Here, we have two blends, Summer and Winter.
Be interesting if others have tried it, and where.
I may at some point, right now got too many others items to deal with.
I understand our New Zealand 95 RON fuel is somewhat equivalent to the USA 91 anti knock scaled fuel. Our NZ 95 may or may not contain ethanol depending on the supplier.

We also have different blends in the North and South Island and in season. But you have to dig around to actually find that out. It is certainly not advertised by the retailers.

RON 91 is the standard fuel in NZ with 95 and 98 RON also available. I used 95 in my Commando.

From the NZ AA website.

“The specifications in New Zealand are generally close to those in the European Union, with some biofuel specifications similar to those adopted in the USA. In New Zealand, both petrol and diesel have their specifications seasonally adjusted in relation to climate variations. With petrol there are three geographical areas: Northland and Auckland, the rest of North Island and the South Island. For diesel, there are two ‘seasons’ – summer and winter.”

Now what all that means for tuning in the USA is a bit of a mystery to me. All I can say is the original 3.5 slide recommendation seems to work for me down here.

Maybe I should check on a dyno with mixture analysis sometime.
 
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