I'm working on the intro riff to Layla by Eric Clapton.
Play A open then hammer on 3rd
Play D open then hammer on 3rd follow to a pull off
3rd on A
D open

I'm having trouble with the hammer onto the pull off, Sometimes the pulloff sounds good other times it doesn't sound at all or it's very quiet. Is this just lack of finger strength or maybe bad technique for pull offs? I'm playing slow for now and will work up to actual speed when it's absolutely perfect.
If you've only been playing for a few weeks its just weak fingers so give it a little time.
I've been playing a little over 2 months.
I have no problem doing the hammer on pull off by itself. It's when I try putting the whole thing together, no matter what speed.
2 months=a few weeks

It's probably a little too soon to be trying something like that tbh. Your fingers aren't so much weak, it's more that you dont have anywhere near the level of control over them you need for this kind of stuff. That will only come with time, it's not something you can force.

Stick with simpler, more chord based stuff for the time being and go back to Layla in a few months time and it should be a little easier.
Actually called Mark!

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Its just lack of technique, as you haven't got that much control over what your fingers are doing yet. You said it sounds good sometimes, so you CAN do, its just a case of getting it consistent. Make sure you're pulling off at a slight angle (rather than just lifting your finger off the string), and that you're not inadvertently muting the string with any other fingers.