sputter on take off

I would inspect the float bowls for debris, I have had similar symptoms in the past where some debris in the carb was getting sucked into the main jet under maximum load. I would also check the fuel filter, float bowl vent lines and make sure that the fuel level is correct in the bowls.

It is also worth checking for split carb mounts and bad ignition leads and caps. I take it the fuel pressure is good when you have the problem?

Thanks, yes, I checked the bowls but didn't check the vent lines.   I have had the carbs rebuilt and the problem went away for a few hours then came back.  Yes, fuel pressure is good.  A mechanic also told me to check the slides in the carbs, as they get stuck.  I have not checked this, but know that there are several points, as you mentioned that I need to check and go back over.  I appreciate the suggestions. 

I would suggest you study the following VAF Thread....  https://vansairforce.net/community/showthread.php?t=194385&highlight=vapor+lock 

Thank you, James.

I read the thread and found several points I will look at as I continue exploring the sputtering on takeoff, e.g., such as fuel blend and mixture. First I am going to look at the slides in the carburetors.  A Rotex mechanic told me slide sticking might be the issue as well as the fuel mix, in that excess air or too rich a mixture might be the problem.