Back to original airbox from pods - Adjustment needed?

Hi guys,

Over xmas I spent some time taking off my pods and putting in the original airbox with silencer. The bike is a 1976 Kz900A4. I also took off a 4-1 marving exhaust, and got in a lovely 4-4 replica exhaust.

Carburation had been done less than a year ago with the pods and the Marving, and the bike worked really well. Points were new and adjusted. 

I went for a test ride today, with the new setup, and it works well up to 4-5k RPMs. It will not go over that, and seems to "surge" when it reaches that range. Bike starts great and idles great. 

I´m a bit lost. Has the engine become richer or leaner? What should I try to get this better? Will ajusting my mixture screws solve the problem?

Thank you!

PD: By the by; I tried the 4-4 without internal baffles, and the bike is way too noisy! Beautiful sound with baffles

You will currently be running too rich and need to ensure that the jet needle is in the middle groove (number 3) and that the pilot and main jet are returned to the original sizes.
This information for the correct jet sizes will be in the workshop manual for your machine.
Be wary of some 4-4 replica exhausts as some are known to be restrictive.
 

Are you seeing black smoke when you hit 4 to 5 krpm?
Ride a few minutes at 5K rpm. Hit the kill switch and pull the clutch lever. Coast to a spot you can check the plugs.
Another way I check for too rich or too lean, is to go for a quick ride with out the air cleaner filter. See if the bike runs better or worst.

What carbs. 26mm with air pilots. Meaning the pilot adjustments will be on an angle off the front of carbs (airbox side) those would be the original. I ask because if you don’t have a manual, I do and will look up factory jet sizes later this evening. I think it’s 15 pilot, 110 main.

Yes. This is my next move. Take out the air filter element and silencer, and see if it behaves differently. 

Thank you. Carbs are stock 26mm. No pilot on the side, but in the bottom of the carb. 

The original jets were 115 main jet, 17.5 pilot jet and 5DL31 needles.  Those are for the VM26SS carbs with the fuel/air screw on the intake side of the carb.  Needles should be in position 3 as zed1015 has said.

wrote:

Thank you. Carbs are stock 26mm. No pilot on the side, but in the bottom of the carb. 

Just FYI, those are factory carbs (stock) but not original to your bike. Claim is they are a tad better then you bikes original. I don’t like them, got tired of melting my hand trying to adjust the #2,3, carbs. 
 

wrote:

Yes. This is my next move. Take out the air filter element and silencer, and see if it behaves differently. 

Just put the carb settings back to stock and you should be good to go.
Removing the filter element etc will improve the current carburation because you will be removing a restriction and leaning off the mixture..
This will increase the air ratio closer to what the current jetting required for running pods but frankly is pointless and a waste of time if you want to run the stock airbox.
Whatever you do apart from refitting the pods etc will require a change of jetting which cannot be avoided or got around by removing parts of the intake to try and match the airflow to the current jetting.

Indeed. I will have to have it rejetted. I just want to try without the filter… but I’ll have to have it done. It’s beyond my abilities

There were two versions of those carbs.  The standard version had 107.5 jets and 5CN8 needles.  The LTD version had 105 main jets with 5DL31 needles and 15 pilot jets.  In both versions the needles were set in the middle (3) position.

A common reason for running rich is the choke plunger seal is worn.  When you pull the choke plunger you can see the seal on the bottom.  zed1015 can rebuild them for you.

OK. Went for a test ride today, taking off the snorkel silencer (the 2-eyed contraption), but leaving the filter in place. The bike ran a bit better, with the ability to rise to 7-8k rpm, but feeling still "heavy". 

Inspired by your comments, I´ve taken the plunge into my main jets, as they can be replaced with the carbs in place. I do have another set of carbs (with a side regulation bolt, as @mikaw said. Findings are:

1.- Current jets on bike are 115
2.- Jets on my other set of carbs are 102,5

I can´t say if the needle is in the 3rd slot, as I don´t want to go into the carbs; but I´m tempted to just plugging in the 102,5 jets, and see how it goes. 

What do you guys think?