Re: 1972 Merc 250 - Zeniths & Webers
A couple of notes I have after working on my Zeniths is this..
how's your muffler? Is it old and crusty? If so it may cause you problems with idle.
I could not get my car to idle smoothly until I replaced the muffler. Likewise leaks in the vacuum effect air pressue in the carbs as will leaking or blocked exhaust lines and mufflers.
With the engine cold, start the engine and put your hand under the carbs and feel for air movement that is not coming from the fan. Do this quickly has the exhaust manifold warms up pretty fast and will burn you. Then run your hands near the exhaust pipes and feel for leaks.
I may be incorrect but I think the test to see if your carbs do have leaks is that if you put a folded shop rag over the top of the car then the idle should go down and if leave it on it should stall the engine. If there is no change in the idle then the carb is still getting air from somewhere.
I have also found that using premium gas really does nothing for your car except burn money.
Since you are in a hot climate then the heat risers in the exhaust manifold that are supposed to warm up your carbs should be permanently closed otherwise they will warp your carbs or warp them again. If the rear carb feels much warmer than the front after the car has been running for awhile then the heat riser is probably stuck open and has probably warped the rear carb. Neither carb should be so hot that it might burn you but if it is then it is probably warped.
MB 72 250 M130.923 114.011 170k The Beauty