Amal chrome slides

Just renewed my carbs bodies and fitted chrome slides on my 850MKII.

Difficult to start from cold and will not pick up from idle unless choke is used. Never had to use the choke before just flood the carbs and the first kick starting.

Carb bodies are 932, new slides 3 1/2, main jet 260. needle jet 106 and needle position centre notch, all exactly as before new bodies and slides fitted.

Can any one point me in the right direction as to fixing this problem? :?

Clean out the primary circuit including probing the pilot jet with a 16 thou drill or similar, new bodies do come with optional extra swarf as quality control is naff, hence why I always use old carbs and resleeve them instead of buying new.

Thanks for your reply, I'll try that next.

I'd blown out all the carb drillings with an air line before assembly, but swarf perhaps would not be dislodged with airline pressure.

Got it taking the throttle a bit better when hot, had to run the pilot jet screws at 3/4 out. Set up the idle and synchronised with morgan carb tune.

Will let it cool off and try cold start again before stripping and poking out the primary drillings.

many thanks for your input

Skoti

Skoti
Don’t assume the needle and needle jet are not worn also. Out of six Amals that I resleeved, I found four out of round. I had access to a shadowgraph scope, which will magnify small parts to show dimensions accurately. If your needles have a frosted look axially then I would replace both. The needle for your 850 should have four grooves. Viton tipped float Needles should be used and set the float to a height of 0.80” thou from the top surface of the float bowl. Roy Bacon Norton Twin Restoration has a number of jet sizes and needle positions. These are good starting points depending on year and Mark of the 850. Exhaust variations dictated the jet sizes and positions of your needle. If you can’t find a 16 thou drill I use an acoustic guitar E string to probe the idle jet. This site has good information on Amal tuning at top. Have a good read.
Cheers.
CNN

CanukNortonNut said:

Skoti
... The needle for your 850 should have four grooves ...

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My '73 850 has chrome slides and they work fine.

The point about the four-groove needle brings up a question for me that someone can probably answer. I think that the four-groove needle (p/n 928/104 - and these are identifying grooves, not needle position grooves) must be used with the notched spray tube (p/n 928/107). Am I right in thinking that this spray tube and needle combo was introduced with the black-cap silencers and the restricted airbox? My 1973 850 has peashooters. It's an early 850 and I have Amals with the regular spray tube and three-identifying-groove needle, and the bike runs well, with no flat spots. The carbs are not original, though, so I don't know what it came with when new.

Skoti: If you replaced your carb bodies you might check whether the spray tube is the correct one for your bike. That shouldn't affect starting, though. I think the pilot circuit is the only part of tha carb that really affects starting. It might have something to do with the bike faltering when you open the throttle, though. I'm not sure.

I've owned my '74 850 MKII from new, it has peashooters and mesh air filter box as standard.

The original carbs have flat top spray tubes fitted as do the replacement carb bodies and the needles have three notches (above the circlip grooves).

The needles are set in the standard centre groove position, the main jet (260) and needle jet (106) are standard.

With the old carbs I run my pilot screws about 1 3/4 turns out. I tried this with the new carbs and encountered starting problems and poor throttle pick up.

I have adjusted new carbs to 3/4 turns out and this seems to have cured the problems.

Shall wait until the morning and try another cold start test.

BTW I once made the error of fitting carb bodies with angled cut away spray tube and that caused lumpy running 2500-3000rpm on light throttle.

Corona
You are correct...I should have clarified Identifier markings and the needle position grooves better… bad choice of words. 750s have 2 id marks and the 850s have 4.
Regards
CCN

CanukNortonNut said:

750s have 2 id marks and the 850s have 4.
Regards
CCN

Click to expand...

CCN: I agree that the late 850s have four ID marks. But my 1973 850's carbs have ordinary, flat top spray tubes and needles with 3 ID marks. So does Skoti's, apparently:

Skoti said:

The original carbs have flat top spray tubes fitted as do the replacement carb bodies and the needles have three notches (above the circlip grooves).

Click to expand...

So, am I correct in thinking that the notched spray tube and 4-mark needle came in 1974 or later with the black-cap silencers and tighter emission requirements?

Corona
My main bodies are
R932/29 and L933/30: with the split spray tubes, 3 ½ slides, 106 needle jet, 260 mains, bike is 1973, 850. I purchased the bike Used so if the carbs are original I can’t be 100% sure. I had them resleeved last year.
CNN

Here is something on split spray tubes... http://www.inoanorton.com/docs/TheNortonCarburetor.pdf

Regards
CNN