Hi!
In the US, Samurais were equipped with a Hitachi carburetor.
One of the first things that I would suggest is to check the condition of all of the hoses on it. As they get older, the hoses leak which affects performance.
You can get bulk replacement hose at any auto parts store.
The key to replacing damaged hose is to do the job one hose at a time. It's pretty hard to keep track of them all if you start yanking them all off at once. If you DO lose track of which hose goes where, do a search for vacuum at Ack's FAQ (click on the link in my signature, below) for an article mapping out the vacuum hoses on a Hitachi.
Do a search for redneck tuneup for a procedure that can clean up the carburetor's jets.
Hope that this helps!