Amal Settings

I've got a single Mk1 Carb on my 73 750 with a 250 main, 106 Pilot, No 3 slide and needle as low down as it will go(Top Groove) I'm running BP7ES plugs and it's running rich and fouling after 50-60 miles.

1st move was just to fit a 3.5 slide and see how that looked, Plugs looked like it was weak (Porcelain pretty white).

2nd was to bring the needle up just one notch, that made the plugs look rich again just like it was with the No 3 slide in.

3rd and current setting that I've not been able to test yet due to a crack in the oil tank bottom mount is to change the main jet for a 260 and put the needle back down again.

Can anyone see any fault in my logic if so I'd be very happy to listen to some advice with anyone who's been there and done that.

Willy, your specs and settings look pretty reasonable for a single Concentric on a 750. The richness is then most likey to come from a excessively high float level. If you drop the bowl and press down gently on the float needle tangs - not the needle itself, the top edge of the float should stop under the rim of the bowl by 0.060" - 0.080" (1.5mm to 2.0mm). To adjust the level, you need to press in or out the needle feed bush in the bowl. Look at the Bushman's article on Amal Concentric set up on the site.

Mick

Maybe 105 Needle jet? It might bring some adjustability into the picture.

Single MK1? Hmmm! I just don't thing you can get enough air to satisfy. Too fine of a line to tune.

I ran a 34 mk2 but really lacked in performance. A detuned Norton is sort of sacrilegious.

That being said, I run a single carb.
40mm Pumper

pvisseriii said:

Maybe 105 Needle jet? It might bring some adjustability into the picture.

Single MK1? Hmmm! I just don't thing you can get enough air to satisfy. Too fine of a line to tune.

I ran a 34 mk2 but really lacked in performance. A detuned Norton is sort of sacrilegious.

That being said, I run a single carb.
40mm Pumper

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The bike runs fine with the single carb and it's performance is not an issue if I could just sort the fouling problem I'd be happy.

ML said:

Willy, your specs and settings look pretty reasonable for a single Concentric on a 750. The richness is then most likey to come from a excessively high float level. If you drop the bowl and press down gently on the float needle tangs - not the needle itself, the top edge of the float should stop under the rim of the bowl by 0.060" - 0.080" (1.5mm to 2.0mm). To adjust the level, you need to press in or out the needle feed bush in the bowl. Look at the Bushman's article on Amal Concentric set up on the site.

Mick

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Hi Mick

I've just read the Bushman article and the float height is something that I've overlooked, I'll have a wee look at that tomorrow.

Mac.

I am a little confused. Is this a new situation with a new carb and setup or a problem that has suddenly surfaced with the MK1 that had been previously running fine?

pvisseriii said:

I am a little confused. Is this a new situation with a new carb and setup or a problem that has suddenly surfaced with the MK1 that had been previously running fine?

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No it's an all new set up, still in the process of running in and trying to get the mix right!

Check that the carb needle and spray tube match.

A flat spray tube needs the 2 ring needle and a notched spray tube uses a 4 ring needle.

I had a fuel fouling problem, but the bike ran good at all revs, but the needle/spray tube were not correctly matched.
After changing the fouling ended.

You could also try the hotter number 6 spark plug.

Bob Z. said:

Check that the carb needle and spray tube match.

A flat spray tube needs the 2 ring needle and a notched spray tube uses a 4 ring needle.

I had a fuel fouling problem, but the bike ran good at all revs, but the needle/spray tube were not correctly matched.
After changing the fouling ended.

You could also try the hotter number 6 spark plug.

Click to expand...

Hi Bob
Yes, my carb has a flat spray tube and a 2 ring needle, I've also just checked my float level as per the Bushmans guide and it's bang on 2 mm from the float bowl edge, so I guess it's down to the jet and needle setting, I've ordered a 240 main and a 105 needle jet to experiment a wee bit more.

Ok I think I've been chasing the wrong demon here, another rider suggested that it might be the Boyer saga with the dodgy connections, I checked that out and replaced the crimps which did look a bit suspect as did the solder on the back of the trigger plate.
That's one element out of the equation but as it's a wasted spark system why would just one side show rich? Although it's a wasted spark system it still fires the plugs via separate coils, both coils were checked on the bench and the resistances were as per the manual however I have heard of these Lucas coils misbehaving when they get a wee bit warm. I decided to replace them with a dual output coil from RGM , I've been out on the bike and it looks like one of the coils had been the culprit .
However despite it ticking over nice and even when it's warmed up it will occasionally cut out, usually as I'm just coming to a stop at lights or a junction, it fires up again after a kick or two ok. I checked this out again while I was riding along at normal speed by pulling in the clutch and coasting(naughty) with the throttle closed, the engine would die but fire up again after I bumped it.

I can't understand why it'll tick over ok but then every now and again just die when coming to a stop. I hate sitting blipping the throttle It makes me look a right boy racer, Suggestions?

Maybe the fuse and holder are oxidized.

Check battery and charging system. Weak Spark?

Blipping the throttle to keep from stalling may cause the fowling issue, contributed by either the weak spark or a clogged pilot. Don't get mad, you might have something floating around in there that causes an intermittent idle issue while cruising.

You mention a 106 pilot in your original post. I think you meant 106 needle jet. Just to cover the bases, check you pilot jet.

Battery
Put a load test to the battery.

Stator
Check the volts at the terminals while running the rpm's up to get some numbers.

Torontonian said:

Maybe the fuse and holder are oxidized.

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How would this allow the bike to tick over at rest but cause it to cut out when coming to a stop?

pvisseriii said:

Check battery and charging system. Weak Spark?

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Battery is getting a good charge on the move, I've got a mounted Voltmeter that shows around 14-15v (actually 13.5-14 at the battery terminals)

pvisseriii said:

Blipping the throttle to keep from stalling may cause the fowling issue, contributed by either the weak spark or a clogged pilot. Don't get mad, you might have something floating around in there that causes an intermittent idle issue while cruising.

Click to expand...

I've not got an inline fuel filter on the bike at the moment except the screens on the fuel taps so that might be a possibility!

pvisseriii said:

You mention a 106 pilot in your original post. I think you meant 106 needle jet. Just to cover the bases, check you pilot jet.

Click to expand...

Yes it is a 106 needle Jet

pvisseriii said:

Battery
Put a load test to the battery.

Click to expand...

Battery is a brand new item

However despite it ticking over nice and even when it's warmed up it will occasionally cut out, usually as I'm just coming to a stop at lights or a junction,

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Willy, despite two sets of new Amals over the years (new bodies from new tooling last time) I have rarely been able to have both a lowish tickover (750-800 rpm) and the ability to stay alight when rolling to a stop. Of course having super clean idle circuit(s) helps but even with the pilot clear I need 1000 rpm minimum. I hear those who claim 600 rpm or less and I don't disbelieve them but I've never been able to achieve that and a reliable tickover when shutting the throttle. Mine is horrible in traffic and once it starts to get hot the carburation goes to pot. There seems to be a sweet temp as you'd expect and then the tickover deteriorates fast as she heats up and tickover revs rise. I've suspected fuel vapourisation in summer but I'd doubt that's your problem given present temps. So the point of this post is......is your tickover now too low? Not sure what's happening inside these carbs when shutting the throttle from speed? maybe someone knows? Do they go overrich because of the increased vacuum when the throttle closes? Does that temporarily rich mixture mess up the tickover settings?

[/quote]
Willy, despite two sets of new Amals over the years (new bodies from new tooling last time) I have rarely been able to have both a lowish tickover (750-800 rpm) and the ability to stay alight when rolling to a stop.[/quote]

I have found that electronic ignition with idle stabilization makes a big difference, assuming the carb is clean and well adjusted. I have a solid 650 rpm idle (MKV 750 with 30mm carbs) with Trispark.

Maybe carb size is relevent with MK 1 Amals.

Keith1069 said:

However despite it ticking over nice and even when it's warmed up it will occasionally cut out, usually as I'm just coming to a stop at lights or a junction,

Click to expand...

Willy, despite two sets of new Amals over the years (new bodies from new tooling last time) I have rarely been able to have both a lowish tickover (750-800 rpm) and the ability to stay alight when rolling to a stop. Of course having super clean idle circuit(s) helps but even with the pilot clear I need 1000 rpm minimum. I hear those who claim 600 rpm or less and I don't disbelieve them but I've never been able to achieve that and a reliable tickover when shutting the throttle. Mine is horrible in traffic and once it starts to get hot the carburation goes to pot. There seems to be a sweet temp as you'd expect and then the tickover deteriorates fast as she heats up and tickover revs rise. I've suspected fuel vapourisation in summer but I'd doubt that's your problem given present temps. So the point of this post is......is your tickover now too low? Not sure what's happening inside these carbs when shutting the throttle from speed? maybe someone knows? Do they go overrich because of the increased vacuum when the throttle closes? Does that temporarily rich mixture mess up the tickover settings?

Click to expand...

My steady tickover is around 900-1000, but I can't really put a finger on, when it'll cut out when rolling to a stop, or when testing it on the move(Coasting), as sometimes it will and other times it won't.
As I have the 2-1 inlet manifold the heat insulating blocks that are normally there with the individual manifolds can't be used so I'm wondering if this might have something to do with it as the heat transfers through to the carb?
The studs on the manifold used to secure the carb are not long enough to have a thick insulating washer in place but this might be a necessary modification if it turns out to be a heat transfer issue.

Willy, despite two sets of new Amals over the years (new bodies from new tooling last time) I have rarely been able to have both a lowish tickover (750-800 rpm) and the ability to stay alight when rolling to a stop.[/quote]

I have found that electronic ignition with idle stabilization makes a big difference, assuming the carb is clean and well adjusted. I have a solid 650 rpm idle (MKV 750 with 30mm carbs) with Trispark.

Maybe carb size is relevent with MK 1 Amals.[/quote]

With the Trispark fitted are you now saying that you don't have an issue with it cutting out when rolling to a stop?
I've got a Boyer system on mine whether or not it has idle stabilization is beyond me, I've read lots of reports about it going Tits up with low voltage, but my voltmeter rarely indicates anything less than 12.5 volts so I'm thinking I can rule that out.
Me thinks I might have to have a wee looky through the pilot orifice and see if there's any gunge in there, but that'll have to wait for 3 weeks till I get back home!

Just remembered another symptom that might possibly be heat related, it feels like the slide is being held up every now and again as the revs fail to come down during a gear change or slowing down (One extreme to the other here) a few blips seem to unstick it, I'm pretty sure it's not cable routing and it has just been lubed.

Hey Willy Mac:

I stripped my Amals down at the beginning of this year and cleaned all the 'wee' holes out with carb cleaner and wire, made a big difference.

However ..... I still find I'm tweaking the carbs (pilot / mixture screws) dependent on climate. It gets warm in Northern California during the summer requiring one set of tweaks and has now cooled to require a different set. I think over time, and my bike has 24,xxx on it, the slides and bores become worn and getting a reliable tune becomes more challenging - I'm thinking of the anodized slides as the next change.

I have not been able to get the bike to a reliable tickover below 1,000 revs and if I can get it to a point where it doesn't cut out when I come to a stop, I'm (relatively) happy. Oh, and I'm running Boyer ingintion.

As I say, I think the main issue is air slipping by the slide / bore surfaces, leaning out the mixture. I'm running with the needles one step down, so a relatively rich mixture.

Just my experience, from a novice spanner-juggler.

BTW - I'm from the UK and the grandparents grew up in Mofat, Dumfriesshire - I'd love to ride around the west coast some day, truly God's country.

- Nellie