can any one help here? shed some light on this subject for me and my grandfather?

 

It is a vacuum operated secondary. When the load on the engine is sufficient, the primary opened to a certain degree and (I believe) the choke open at least 3/4, it will open based on the amount of vacuum present in the primary barrel. It can be reworked to be a manual secondary.

Maybe this writeup could be Helpful, if you want to convert your carburetor's Vacuum operated secondary, onto a more reliable mechanical operated Secondary:

 

~► http://www.ultimatesubaru.org/forum/topic/147163-mechanical-conversion-on-hitachi-carburetors/

 

Kind Regards.

Thanks guys ill see what me and gran dad can do

You're Welcome!

 

Please let us Know what route you'll choose... and the Results.

 

Kind Regards.

I would like to do the mech secondary. The write up isn't all to descriptive so I think my grand dad and I will have small issue fallowing it

... The write up isn't all to descriptive so I think my grand dad and I will have small issue fallowing it

 

I agree that the Writeup is not so Descriptive; the Reason is because it is written / intended for people with previous Mechanical Experience and Knowledge on Carburetors, they'll understand easily the ideas.

 

So if you are newbies in the Carburetor escenario, it is better idea to take your Carburetor to a Professional mechanic, or someone who has more experience with carburetors, otherwise it could be Dangerous to play with it, for your safety and health.

 

Remember: Carburetion is somehow an Art, while Fuel injection is a science, to play with a carburetor is like playing with Fire and Gasoline, so please do not misunderstand me, I'm not disrespectful nor rude, I'm only concerned for your safety.

 

Kind Regards.

If the modification seems difficult for you, call Carbs Unlimited, in Kent. They deal with Hitachi carbs. Check their websites first.