sometimes trying to repair these is difficult to 'get it right the first time', it's generally quicker and less time involving to just get a new one or reman one if available and swap it out.

Basically, problem with engine goes idle was solved after we cleaned carburetor. But engine still starts very bad. We found that the problem is he gets too much fuel. There is a main hose from a regulator to the carburetor. When we are taking this hose off during the engine starts we are reducing the amount of fuel and the engine starts properly. So my question is how can I reduce fuel flow. This AISAN type C regulator seems doesn't have a manual regulation. The lock-off valve seems works fine.

Mine turned out to be the injector. Good luck with yours.

Check your fuel shut off solenoid- I would bet it's gummed up. Installing a coolant thermostat in line with the regulator works wonders

lukaz if you need any further help give us a serial number of the truck
also the engine series and fuel system make. Impco or Aisan?

without this info i cant help you

I get the same code on an H60FTM. It is normally hard to start. Have to crank it for about 10 seconds before it will fire. Then it runs well. If I give it a shot of ether it will start much faster. Did you try ether? The operator tells me it just dies out sometimes but I haven't seen that happen, yet. Would help if I knew a bit more about the theory of the system.

DTC 522655-1 - Short Term Closed Loop Correction Bank 1 Greater Than NOR 40% (Lean Engine Operation)

Common problems that may cause lean codes:

- Contaminated/clogged trim fuel injector's filter and/or LPG regulator's filter
- Contaminated/clogged trim fuel injector
- Faulty trim fuel injector or wiring
- Contaminated LPG fuel
- Low primary LPG fuel pressure (for trim fuel injector)
- Low secondary LPG fuel pressure (for carburetor)
- Clogged fuel hoses
- Contaminated/dirty carburetor
- Faulty fuel shutoff solenoids
- Engine overheating
- Exhaust leaks prior to or near oxygen (O2) sensor
- Manifold vacuum leaks
- Improper ECU grounds on engine block
- Faulty ECU injector driver 2

Thank you both for your answers. Still working on it.
Sometimes there is error code 522655-1 on te display for few seconds then disappears.

plenty of things can cause this
edwards suggestion is certainly a problem to check

also you might want to:
look for vacuum leaks
check the ignition system
check the engine sensors
check your grounds
check the connections at the ECM

but first and foremost are there any DTC's showing up on the display?

as far as the "Searching" for engine speed, you may need to pop the clips off the plastic side of the throttle body, use compressed air (and a dust-mask for you) and blow out the accumulated dust from the corners of the throttle body.