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ok this blower is beating me up. It will now run only with choke on and starting it with carb cleaner. Ive replaced the carb, filters bulb, spark plug and the two lines out of the tank. Any suggestions?

You didn't mention adjusting the valves. #1 problem with the 4-Mix units. Must adjust valves at regular intervals. Not certain, but I think they are set at 0.004".

Insert feeler gauge 4180 893 6400 (1) between rocker arm and valve stem. The feeler gauge must slip through with a certain resistance.

Inlet valve = 0.10 ± 0.02 mm
Exhaust valve = 0.10 ± 0.02 mm

Also would not hurt to check the muffler's spark arrester screen.

I will take a look. I didn't think about the valves it is kind of a hard pull and that should take care of that

Nothing helped

If it only runs with the choke on then it is not getting enough fuel
That leaves you with two options
1) carb is not putting enough fuel into the charge
2) air is entering after the fuel has been mixed into the charge

To check for the latter start the blower then saturate the area between the carb and the block with WD 40 or similar from a trigger pack, not a Spray can ( fire risk ) .
If the blower stops or blows white smoke then there is an induction leak.

If that makes no difference then after running the blower for a few minutes, either pull the fuel line off the carb or open the fuel cap.
The fuel tank is pressurised by the return line form the pump
If the tank is not holding pressure not enough fuel will get to the carb.
The pump does not suck very well, like most pumps it blows and the blowing increases the pressure in the fuel tank which forces the fuel up to the carb.
This is paticularly important in back packs because the carb is a lot higher than the tank so the fuel has a long way to go against gravity .

No pressure, possibly bad vent?

Sounds like it
The tank should hold 7 to 10 PSI same as most cube carb engines .
All of my customer have the bigger 600 & 700 series that have a stand alone tank vent
The 400's have a double vented cap if you have the standard tank or a single vented cap & pressure valve with the bigger tank.

There was also a problem with fuel pick up when the tank was tilted so there is a new tank that uses 2 fuel filters one of which has 2 barbs so one filter sits at either side of the tank
The bigger blowers have a tank bung with 2 inlets and it has to be fitted the correct way with the inlet tubes crossing over each other ( left side filter feeds right side inlet & visa versa )
Not sure if this set up was used on the 400 as well.

Then I must be understanding the following 400 fuel cap wrong as I see two filters and one check (vent) valve.

Replaced the vent and checked for air leaks with a can of carb cleaner and I am not finding anything. I can still get it to run on choke. After it runs I pulled thd fuel line from the carb and there was still plenty of pressure. Any other ideas?

Are you using proper fresh feul?
Check the flywheel key, with these models they break sometimes.
Check the compression engine might be worn out?

Plenty of compression. Ill check the flywheel key in the morning

Key was fine. Im beining to think the carb is messed up from the factory

In this situation i would do a leak test. Block off the exhaust port an put air pressure on the intake. Do this with a manual air pump. DO NOT go over 0,8 to 0 9 bar when doing this! So you know for sure the engine is air tight.

Did anything change after you changed the carb or is the problem still exactly the same?