Problem tuning dual KEI HIN carbs on a EA-81

[Underground boy]

My father and I decided on using a SUBARU EA-81 1.8liter engine on a motor handglider. It's all OK bacause the engine is light and powerfull. The problem is that we had to make some changes and rebuild it for a flying machine. We removed the original carb as it is way too complicated and unusefull for our purpose, as well as there was no place for it in the middle of the engine. From a local friend we bought two KEI HIN carbs, which were from a group of 4 for a Kawazaki motor I think. We installed a metal tube about 15mm or something that connected the 2 inlets together between the carbs and the heads. This is to remove the difference in the 2 carbs if there is some. We encountered that the carbs gave way too much air that was needed for the specific RPM. I don't know how cc is the motor we have taken the carbs from but i think we have a big difference here. If the Kawazaki is 1000cc /for instance/ and it is using 4 of these carbs it comes that a single carb drives 250cc. In our case we are trying to make 2 of them drive 1800cc. 4cyl. This is makes 450cc for each cyl which is about twice as much as the original. Another thing which contributes to our problem is that each carb drives 2 cyl one after another and in the time while the other head works it is not used.
The kei hin carbs are horizontal and look much like 2-stroke ones outside. Operating the gas you rotate an air-valve as a normal 4-stroke carb. Before it there is a sliding rule which moves automatically up and down delivering the right amount of air needed. We think that the bigger cyl makes more vacuum in the carb and moves this rule up more than usual which makes the air-fuel mixture deficient in fuel.
The engine should make around 5200RPM and to this moment it gives only 3000. I would be thankful for any suggestions given on this problem!