Cold Idle Question

Mart UK · Aug 15, 2021

Hi, I'm still very new to my 1975 850 mk3. Just looking for some reassurance... I have a single Amal 34 carb, with choke. Even in the warm weather, I need the choke on to start (always first touch of the button now). Then I turn the choke off straight away and keep it running using the throttle. After about 30secs it ticks over on it's own, but below 1000rpm. The red ignition light comes on unless I blip the throttle. If I'm still putting my helmet/gloves on, I intermittently blip the throttle to 2,000rpm. If I hold it steady at 2000rpm I can detect an occasional miss (hiccup). By the time I've ridden to the end of my lane (800yds), it ticks over at 1200rpm, no red ignition light and no miss. I then turn the ignition the next step, to light the headlight. The bike rides great this last 1,000 miles, since you all helped me with the primary side issues I had, plus new plugs and carb cleaned and refurbed. When fully warm, no hiccups or ignition warning light. Pulls smoothly and ticks over regularly, at 1200revs.

Im pretty sure all is OK, but just thought I'd check: Is this cold behaviour all normal? Thanks.

dero · Aug 15, 2021

Mart UK said:
Hi, I'm still very new to my 1975 850 mk3. Just looking for some reassurance... I have a single Amal 34 carb, with choke. Even in the warm weather, I need the choke on to start (always first touch of the button now). Then I turn the choke off straight away and keep it running using the throttle. After about 30secs it ticks over on it's own, but below 1000rpm. The red ignition light comes on unless I blip the throttle. If I'm still putting my helmet/gloves on, I intermittently blip the throttle to 2,000rpm. If I hold it steady at 2000rpm I can detect an occasional miss (hiccup). By the time I've ridden to the end of my lane (800yds), it ticks over at 1200rpm, no red ignition light and no miss. I then turn the ignition the next step, to light the headlight. The bike rides great this last 1,000 miles, since you all helped me with the primary side issues I had, plus new plugs and carb cleaned and refurbed. When fully warm, no hiccups or ignition warning light. Pulls smoothly and ticks over regularly, at 1200revs.

Im pretty sure all is OK, but just thought I'd check: Is this cold behaviour all normal? Thanks.

Sounds OK to me .

kommando · Aug 15, 2021

You tune the pilot circuit for best running on a warn engine, this means it runs rubbish cold as other than the mixture being rich there is nothing to keep the revs up. On a single concentric MK1 carb you have the option of an extended throttle stop screw which I use on all my singles, before a cold start you screw it in 1 to 1.5 turns for a higher tickover, the extension means you can turn the tickover down as the engine warms with a gloved hand.

jbruney · Aug 15, 2021

Mine is very cantankerous until it warms a little.

Mart UK · Aug 15, 2021

Looks like all normal then. I'm perfectly happy with the cold start routine, so long as that's how it works. It's a mk2 concentric Amal, it has the idle speed screw, but I don't fancy messing with it each ride, took me a few runs to dial it in right for warm running, as the best position for the pilot air screw (once I'd worked out the best size) seems sensitive to the idle setting. Thanks. I'll leave alone and continue to enjoy riding it...

daveparry · Aug 15, 2021

Mart UK said:
Hi, I'm still very new to my 1975 850 mk3. Just looking for some reassurance... I have a single Amal 34 carb, with choke. Even in the warm weather, I need the choke on to start (always first touch of the button now). Then I turn the choke off straight away and keep it running using the throttle. After about 30secs it ticks over on it's own, but below 1000rpm. The red ignition light comes on unless I blip the throttle. If I'm still putting my helmet/gloves on, I intermittently blip the throttle to 2,000rpm. If I hold it steady at 2000rpm I can detect an occasional miss (hiccup). By the time I've ridden to the end of my lane (800yds), it ticks over at 1200rpm, no red ignition light and no miss. I then turn the ignition the next step, to light the headlight. The bike rides great this last 1,000 miles, since you all helped me with the primary side issues I had, plus new plugs and carb cleaned and refurbed. When fully warm, no hiccups or ignition warning light. Pulls smoothly and ticks over regularly, at 1200revs.

Im pretty sure all is OK, but just thought I'd check: Is this cold behaviour all normal? Thanks.

All sounds completely normal!

baz · Aug 16, 2021

Sounds spot on
If it idled straight away from cold it's too rich

cash · Aug 16, 2021

The Mk2 has an enrichment circuit not a choke and it only has an effect over small throttle openings. It has the advantage of giving a higher tick over when in use. You might find it better if you try changing the standard jet from #50 to say #30.
But would it be worth the bother?
Dave

Cold Idle Question

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