OK my 1970 521 starts ok but after a few minutes starts to really lope theres no tack but I was wondering which scews are the fuel and air adjustment....I imagine this is the stock carb its got the big glass window on the side and its about 3/4 full.......everything seems to be working good but the plugs were pretty black....thay look new and I cleaned them up..cap is new and coil doesn't look original...any ideas ???????????

Carbs can be a pain!

Try looking here, there is a stock Hitachi carb breakdown in the tech section on the old 620.com web site. zerothread/379438 This would tell you what each part is on the carb and where they go.

As far as the loping after warm up.....check your vaccuum lines if any, then look at the jets. Maybe you are not getting enough fuel after warm-up? Does it rev ok?

It revs ok but it just will not idle after 4-5 min with or with out choke. Could ignition be week or do you think it could be timing, points any ideas would be great. I don't have anyone who understands these old points and stuff in my social circle.