Amal Premier Throttle Return Springs

Hi All-

After fitting new Amal Premiers to my ‘74 MKII Commando, I am very impressed with the improved performance of my bike.

It seems, however, that excess pressure is required to turn the throttle. Just wondering if the return springs in the carb body fitted to the Premier carb are stiffer by design or if I have something else going on here. It doesn’t appear to be a cable routing issue, but I am open to suggestions. Also wondering if others have noticed the same stiffness with the Premier carb setup.

Thanks for your comments!!

Tom

Not sure. When i put my Premiers on a couple years ago the guage of the spring metal seemed more flimsy rhan on the knackered old Concetrics i pulled off.

Never validated that, however, and the springs could have been sprung on the old ones even if they were heavier guage.

Maybe your old ones are...old?

Yes. I notice that some of my springs are longer than others, a lot longer. I find the twist effort to be too much. I have read that heavier springs keep the slide from bouncing up and down.

I have just been messing with my 850 carbs, now fitted with the new Hard Anodised throttle slides and noticed they would not lift all the way to the top. Further investigation showed that the return spring on one carb is .030" bigger in outside diameter than the other and this is enough to coil bind the spring in the valve before full travel is achieved. This is because the spring increases slightly in diameter as it is compressed and in this case exceeds the diametr of the recess in the valve.

Hope this is of some help to someone experiencing problems

Cheesehead Commando said:

Hi All-

After fitting new Amal Premiers to my ‘74 MKII Commando, I am very impressed with the improved performance of my bike.

It seems, however, that excess pressure is required to turn the throttle. Just wondering if the return springs in the carb body fitted to the Premier carb are stiffer by design or if I have something else going on here. It doesn’t appear to be a cable routing issue, but I am open to suggestions. Also wondering if others have noticed the same stiffness with the Premier carb setup.

Thanks for your comments!!

Tom

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They do seem stiffer but that may be the difference in new and old springs. The Amal part number for the throttle return spring in all MK1 standard and premier carbs, both 900-series and 600-series is 622/131. They also have 622/277 for the 600-series carbs that are called Lightweight. The 622/277 springs are quite a bit lighter but they are also quite a bit longer. I see no way that they would work in 600-series carbs. They should work in 900-series carbs but I've never tried it.

marshg246 said:

They do seem stiffer but that may be the difference in new and old springs. The Amal part number for the throttle return spring in all MK1 standard and premier carbs, both 900-series and 600-series is 622/131. They also have 622/277 for the 600-series carbs that are called Lightweight. The 622/277 springs are quite a bit lighter but they are also quite a bit longer. I see no way that they would work in 600-series carbs. They should work in 900-series carbs but I've never tried it.

Click to expand...

The 622/277 springs were specified for Triumph triples which use the 600 series carbs so won't be too long to fit. Check that the outside diameter is not expanding enough as the spring compresses to coilbind in the slide. Just discovered this happening in my 850 fitted with the hard anodised slides (as per Premiers)

plumridge said:

The 622/277 springs were specified for Triumph triples which use the 600 series carbs so won't be too long to fit. Check that the outside diameter is not expanding enough as the spring compresses to coilbind in the slide. Just discovered this happening in my 850 fitted with the hard anodised slides (as per Premiers)

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Actually, today Amal simply specifies them as 600-series. In a non-triple, non-premier they bunch like a snake and don't work well at all. A standard spring with one loop cut off is better. I haven't checked them against the original 622/277 springs in my Triples. In a hard anodized slide, the spring is in a tube which prevents snaking part way up but could cause even more above the slide - I have no proof of that. The 900-series carbs are so much taller that I don't think cutting a loop would work - haven't tried. I asked Amal long ago for a standard length but lighter spring - they weren't into it - fear of the throttle sticking open.

I have a huge box of old 900-series carbs. I'll compare some old springs to the new in the next day or two.

Cheesehead Commando said:

Hi All-

After fitting new Amal Premiers to my ‘74 MKII Commando, I am very impressed with the improved performance of my bike.

It seems, however, that excess pressure is required to turn the throttle. Just wondering if the return springs in the carb body fitted to the Premier carb are stiffer by design or if I have something else going on here. It doesn’t appear to be a cable routing issue, but I am open to suggestions. Also wondering if others have noticed the same stiffness with the Premier carb setup.

Thanks for your comments!!

Tom

Click to expand...

Interesting. I bought a pair of Premier carbs about 2 years ago. And if anything the pull is too light. Slides never stick so that's not an issue, but the throttle is maybe a bit sensitive especially on a bumpy road.

Maybe they have therefore made a recent change to make them a bit stronger.

I took one new factor y sealed spring from stock and took three springs from random old 900-series carb. Here are the measurements:
Current shipping standard spring: 3" free length, 0.049" wire diameter
Old spring 1: 2.930: free length, 0.048" wire diameter
Old spring 2: 2.875" free length, 0.045" wire diameter
Old spring 3: 2.95" free length, 0.049" wire diameter

Squeezing between thumb and index finger - they all seem the same (I know it's a silly test but it's what I can do).

I'm thinking the difference might be that the hard anodized slides don't let the springs deflect as much and therefore make them more effective (feel stronger).

I don't have any lightweight springs left in stock so I can't measure them. I did find several carbs with at least one coil cut off so I guess people have been doing that for a long time even in 900-serials carbs. These are not carbs I used, they came in a big parts stock I bought.

The problem I was having was not that the spring was too stiff or too long. It was just too big in outside diameter. The wire guage was the same for both springs, as was the number of turns and the overall free length. The problem arose because the spring "grows" in overall diameter as it compresses and the coils flatten out. This then caused the larger diameter spring to bind in the slide hole it sits in before full travel was reached.

If you are experiencing an overly stiff action then you probably want to look at cable routing and lubrication and how free your twistgrip is to spin on the handlebars. You would amazed at how many poorly fitting twistgrips I get to see. Not forgetting of course how well the slides go up and down on their own and if the choke slide is rubbing it causing friction