Newbie rejetting MK3 for new filter - Please Help!

This is my first post, but I've been lingering for quite awhile.

I've searched the archives and even though this would seem to be a common topic, I'm not finding anything really related.

I'm currently restoring my dad's MK3. I've restored 3 BMWs, one being a nut/bolt complete restoration, but this is my first british bike.

I currently have it down to the engine sitting in the frame, sitting next to a small fortune in new parts I've purchased for it.

It did not come with the original airbox and I'm converting it to pea shooters. I've bought a set of Premier Amals.

From what I've read, the original MK3 airbox is crap and since buying/finding a new one is not cheap, I'm not super excited about going that route. It came with a K&N that the previous owner (not dad) put on it.

I've kept my BMW's intakes all original because I've read about all of the horror stories of searching for the elusive perfect jetting. In fact, I obtained one of them at an obsenely low price because the previous owner was tired of trying to make his non-original carbs work correctly (I converted it back to stock). I really don't want to have to screw around with this too much as I'm just not experienced in troubleshooting an improperly jetted machine.

So...
1) Do I go original? Do I go with the K&N? If not, what?
2) Considering the pea shooters and the non-original filters, what jetting do I put in the original carbs to compensate for the higher flow rate?

Do I just bite the bullet and put the original air box on and hope that the pea shooters don't alter the flow that much? Or does someone almighty and wise have the magic answer that I'm searching for?

Steve

I would use the K&N. An 850 with peashooters usually wants a 260 main jet and if the carbs are original with the long needles start with the clip in the middle groove.

I don't like K&Ns on the Commando. They don't breathe as freely as the earlier air filter, although they are a lot easier to work on.

By using the reverse cone silencers, you're effectively reverting to the earlier specification. I run my Mk3 on them, with no balance pipe and the 750 / 'non A-suffix 850' paper air filter and find it fine on the 260 mains used by the factory on the earlier model.

You may need to play with needle position but you shouldn't need to change the slides. Bear in mind that the black box 850s had special cutaway spray tubes and specific needles which need to be kept with them. They will work quite happily though with alternative filters.

I just completed my mk3 rebuild, with peashooters and original airbox, 260 main jets were perfect, 106 pilots. I have spare airbox, if interested pm me for price.

Great, thanks all. That'll at least give a baseline to head down.

I was thinking of heading down the path of using a 750 airbox/filter or one of the various aftermarket individual filters may be the way I go. Sounds like I should start at 260 mains more/less no matter which way i go. Also worth noting is that I'm dumping the crossover head pipes as well.

Really appreciate the replies.

I run a MK2A with the plastic black box air filter with peashooters and it runs best with 260 mains, not sure where the idea came from that the black box is bad as once you get rid of the restrictive silencers and rejet the carb the bike runs fine. Mine came with peashooters and kept the 230 mains and could not run properly at the top end until the 260's were fitted.

The crossovers add mid range torque but its difficult to find replacements and they crack too.