TOPIC:

So my 81 kz650csr runs great without air filters, I purchased the bike as a basket case and there is no airbox. Bought a set of 4 pod filters on amazon for like 20$

The bike will barely run past 1/4 throttle with the pod filters installed. I remember seeing some kind of mod where an extra jet was installed into the throat of the carbs that supposedly helped these things run better with pods, but Im having trouble finding it right now.

Ideally I would just buy an airbox but they are kinda expensive. Anyways, I would appreciate any info related to this topic.

Your talking about the air corrector jets that zed1015 makes. They flatten out the off idle stumble. I'm not sure that's what your experiencing. 20 dollar pods are where your problem lies. Cheap pods can restrict the air flow even more than the stock box / filter set up. Additionally, they can cover the pilot air intake completely.
You say it runs fine without the pods so that's where your problem lies. 
Either refit an air box and filter or buy quality pods. 

If it runs fine without any air filter(s) it sounds like it has been re jetted from stock.  What size jets are currently in the carbs?  
As was stated some of the less expensive pods have a lip on the rubber part that attaches to the carb that alters or blocks air flow to the air jets in the intake bell of the carb. Some also have less air flow than a stock air box and filter do.  Good pods flow more air than the stock setup does and do require some re-jetting to work well.

Not to put words in zed's mouth, but as I understand it he suggests keeping all stock jetting except to increase the main jet size and add the air corrector jet in the main air jet location. 

 

 

I agree that the cheap pods will be the cause of the poor running and they should be avoided like the plague.
Use only good quality free flowing well known brands such as K&N, S&B, APE, UniFilter, Pipercross or Ram Air..
With the air correctors ALL carb settings remain stock apart from a small increase of the mains .
I can supply the air corrector jets via PM if required.

These are your carbs and the ports that you don’t want to block. I’d be tempted to back the pods off an 1/8” just as an experiment while you wait for new better pods. Then you’ll know if the pods you have are too restrictive or covering the ports or both. If it’s just the port holes maybe take an exacto and cut that part out. Then just watch that the filter material doesn’t disintegrate on you and into the engine. Which all pods will likely at some point do.

Gd4now +1. It should be lean without any filters or box. It must be jetted real fat. I’d be looking at what Jets are installed. 

If the carbs are the stock set and the bike was intended for the US market they would of stock had an accelerator pump. For other markets it would not have a set with the pump. There are differences between them. Which set do you have?

You'll need to check what jets are installed. The main jets & pilot jets are easily accessed/removed.  They should have numbers on them. Typically w individual pod filters, the main jets would be in the 110-120 range or thereabouts (stock is #92.5 for US models) & the pilot jets would be #17.5 (stock is #15).  An aftermarket exhaust system such as a Kerker 4-1 w pods would need main jets closer to the 120 end of the main jet range in general.  On the US models the stock jet needles don't have any grooves. If yours have grooves, then they've been swapped out.

As for an airbox, you can probably use one from a 77-80 KZ650 & new ducts are still available. The 650-CSR airbox is actually a KZ750E/H airbox, so you could get one from one of those models or a csr of course.  But the ducts for the 81 csr are NLA & are unique to the 81 model. So you'd have to get the 750 ducts then make up the difference where they fit onto the carburetors by making donuts from radiator hose or something.  Someone on another forum did this. Old used ducts have typically hardened & are no good.

Manual. If you don't have a manual, there's a 1981 KZ650 FSM floating around the internet. The jarlef z650 site has it in the Files section.