Misc: Ignition ATD Hangup

[van drenth]

As a number of you will know recently I have been looking at and working on the Lucas ATD fitted as standard to our Vincent bikes.

After a full refurb of my ATD that included new and stronger springs I find that more often than not it performs perfectly for around the first 200 miles immediately after the refurb but after that, when the motor is cool it still works well but once the motor reaches operating temperature the motor is very reluctant to return to idle. With the bike in gear I can slip the clutch to get the motor to idle, but then it returns to much higher revs when the clutch is pulled in or the bike put into neutral.

I suspect that for whatever reason the ATD is not returning to its fully retarded position. I have rechecked the ATD springs and they are pre-loaded in the retarded position.

Anyone else had/having this issue? Any suggestions?

not enough play at the moving parts when hot.
van Drenth JC

 

[Martyn Goodwin]

not enough play at the moving parts when hot.
van Drenth JC

Than you - I checked and there is around 0.012 inch end float in the ATD so I think it is not an issue with its moving parts.

Have checked my existing Amal today and there are signs of much wear, so a new carb looks like it will be the fix.

As my Comet is a rider, not a show pony, I am looking at the Mikuni options.

Anyone fitted a Mikuni to a Comet?

 

[Comet Rider]

Hi Martyn,
I have been running a Mikuni on my Comet since the day I built it some 15+ years ago.
I am running a 34mm, which I now think is a little large for normal use, a 30 or 32 would probably have been better.
I can speak to my carb guy and get a basic setup price if you would like

Neil

 

[Martyn Goodwin]

Hi Martyn,
I have been running a Mikuni on my Comet since the day I built it some 15+ years ago.
I am running a 34mm, which I now think is a little large for normal use, a 30 or 32 would probably have been better.
I can speak to my carb guy and get a basic setup price if you would like

Neil

Hi Neil,

That would be great - say a 30mm? What did you do about a manifold?

Martyn

 

[Comet Rider]

Hi Neil,

That would be great - say a 30mm? What did you do about a manifold?

Martyn

Hi Martyn,
I made my own manifold using aluminium handrail which was 34mm ID.
I'll let you know about pricing ASAP

Neil

 

[stu spalding]

Hi Martyn, you could get away a turned brass collar sweated onto the standard manifold. Pictured are the collars I used with Mk2 Concentrics. Cheers Stu.

 

[Bobv07662]

Hi Neil,

That would be great - say a 30mm? What did you do about a manifold?

Martyn

Martyn, before my Rapide's 1996 renovation it had Mikuni carbs on it. They have been passed down ever since and now reside in my spares boxes. If you need any photos or info about the carbs let me know and I can investigate them and/or post photos.

 

[Martyn Goodwin]

Just found that the spares Co do a manifold for a 30 mm Mikuni - the 28 mm one is also listed but out of stock.

 

[Martyn Goodwin]

So now I am trying to nail down the settings for a 30mm Mikuini

 

[Martyn Goodwin]

I had a Commando here before Christmas that had done about 26,000 miles on a set of new Premier concentric's, in my opinion they were near worn out. The wear in the slide guides was amazing, i had to dremel away parts of the bore to fit new slides.........

Today I stripped down my Mk 1 Amal premier and found small burs in the edges of the groove that the slide locating pin travels in, they were down towards the bottom of travel, like where the slide sits when the throttle is closed. I carefully removed those burs, as suggested by Greg and tomorrow I plan on heading out for a run, around 100 miles, to see if it has made any difference to the idle speed once motor is hot and I come to a halt with motor running.

Stay tuned