Carb Slide Sticking - Only When Bike is Running

I have a single carb setup with an Amal MKII. I just got the bike up and running and want to move into dialing the carb (the jetting doesn't match some of the recommended settings I've seen) but an immediate problem I'm having is that the slide sticks, but ONLY when the bike is on; and it's not consistent.

The slide springs back beautifully when the bikes off—no drag at all. When the bike is running, it'll sometimes stay at about 1/4 throttle for a good 30 secs or so, then calm down to normal position. There's no air filter on there right now so I can watch the slide go up and down and it's definitely staying open. Throttle cable is free, all should be in working order, as far as I can suss out. I'm wondering if it's some kind of suction thing?

I'm thinking of switching to a Mikuni anyway (just have to figure out if I want VM or TM but that's a convo for another thread ) but it's bugging me that I can't figure this out and I'm just curious.

Any ideas or suggestions would be great. Thanks!

It's common for a single carb slide to stick under the draw of a Norton.

Use a tougher spring. I have, in the past, simply stretched out the stock spring a bit to increase its resistance. Being that it is a single carb, you could reasonably add a spring with twice the resistance, if needed, and still have a comfortable pull.

Considerable discussion on carb slide sticking at the link below. Let us know if any of the descriptions offered in the link are common to your situation.

http://www.accessnorton.com/mk2-carbs-t23822.html?hilit=slide

pete.v said:

It's common for a single carb slide to stick under the draw of a Norton.

Use a tougher spring. I have, in the past, simply stretched out the stock spring a bit to increase its resistance. Being that it is a single carb, you could reasonably add a spring with twice the resistance, if needed, and still have a comfortable pull.

Click to expand...

Nice yeah, that's what I was thinking. Seems like a vacuum thing. I'll poke around the hardware store for a spring to add or replace. Would it be totally crazy to add a bit of lube to the slide as well? WD-40 or a light coat of engine oil? (I sense a lot of flak coming for that question...)

WZ507 said:

Considerable discussion on carb slide sticking at the link below. Let us know if any of the descriptions offered in the link are common to your situation.

http://www.accessnorton.com/mk2-carbs-t23822.html?hilit=slide

Click to expand...

Thanks for the link. I read through the thread but I'm in California so I don't suspect it's a moisture/weather thing.

Had the same problem, stretching the spring only worked temporarily. After fitting a (heavier) chromed brass throttle slide never experienced any sticking again :idea:

the chrome/brass slide should solve the problem but why not go to a single 34 MM Mikuni VM? They are cheap on EBAY, under $100, just make sure it comes with a 2.5 slide otherwise no bargain. The proper jetting has been posted here a million times

nortonspeed said:

Had the same problem, stretching the spring only worked temporarily. After fitting a (heavier) chromed brass throttle slide never experienced any sticking again :idea:

Click to expand...

That makes sense. I saw that the chrome slide is spec'ed by people for this application and I was wondering what the difference would be.

seattle##gs said:

the chrome/brass slide should solve the problem but why not go to a single 34 MM Mikuni VM? They are cheap on EBAY, under $100, just make sure it comes with a 2.5 slide otherwise no bargain. The proper jetting has been posted here a million times

Click to expand...

Yup, I'm trying to decide between a VM and a TM. Seems like people like the TM but I've noticed a lot of the kits sold by reputable people (Rocky Point Cycle, Colorado Norton Works) are VM's. I spoke with the guy from Rocky Point and he mentioned that VM's perform better down low, which is where most people want the power for a Commando, and that the jetting is more dialed in.

I noticed RGM sell a heavy duty spring for MK2s, I'D try the chrome slide and heavy spring