How to adjust the idle on a 350 cc Scrambler 1974 (Amal carb) ?

[Rocla]

Hello everybody,

I have a Scrambler 350cc 1974 which was built in Spain, with Amal carburettor. The idle is not stable and the engine is powerless at low speed... Has somebody the manual for adjusting the iddle with feww pictures and explanations? Or just the process to follow (with the 2 screws) ?

Many thanks

Here below the link to my model:

http://strv.pagesperso-orange.fr/strvmo ... alerie.htm

http://strv.pagesperso-orange.fr/strvmo ... Ducati.htm

Claude

[Nick]

If the slide is worn, air can pass around the slide, making the idle unstable. The cure is to get a new slide. You can also have the carburetor 'Sleeved'. There is a company in the U.S. that puts a stainless steel sleeve around the slide. I'm running sleeved Amals on my BSA and they work fine. The company advertises on Britbike.com

Another possibility is improper air screw adjustment. The starting position for the air screw is one and one-half turns out from fully bottomed. With the bike running, set the idle slightly high and turn the air screw in or out about one-half turn until the engine runs best. Turning the air screw out leans the mixture; in richens it.

Of course, the ignition timing must be correct and the valves properly adjusted.

You can also simply buy a new Amal. They are said to be very good.

[Jordan]

Spanish made Amals are somewhat different from the British made ones.
Some info here:
http://www.britcycle.com/Manuals/amaltune.pdf

[Rocla]

Hello both,

Many thanks. I think I mainly need support to know how to deal with the 2 screws. The first to be adjusted? And the process to get the better idle...

[Jordan]

Study page 9 of the link I posted.

If it's unclear, please ask what part you need help with.

[Rocla]

Thanks Jordan,

Page 9 is very nice, but a little bit complicated. In fact, I've followed a classical procedure which I've found on internet : put the engine at 2000 rpm, once the engine is hot, turn down the throttle screw, then turn up the richness screw up to the highest and steady engine speed possible. Then decrease the throttle position at the normal speed.

It looks like the procedure recommended for my 2 stroke MZ 250cc. Maybe it is sufficient ? The iddle seems to be more regular... I have another problem on my carb : the screws turn by themselves, as they were free... I've put silicon on their head in order to stuck them to the carb body...

Not very orthodox but I hope it will be efficient

[Jordan]

The iddle seems to be more regular... I have another problem on my carb : the screws turn by themselves, as they were free... I've put silicon on their head in order to stuck them to the carb body...

Do you have installed the small O-rings, that fit in grooves in the throttle stop and idle mixture screws?
They provide some friction, to keep the screws from turning, once set. The screws can become loose if the O-rings are worn.

[Rocla]

Hello,
No, I didn't remeber if the screws have o-rings even. I'll check! Many thanks