Date registered: Jan 2007
Mentioned: 2 Post(s)
Quoted: 85 Post(s)
The Zeniths are fine carburetors, but they suffer from warping because of excess heat from the exhaust manifolds. This is caused by the flaps in the heat riser mechanism sticking in the open position, rather than closing as the engine warms up.
Once the warping, usually of the top plates, occurs it is nearly impossible to get the carbs to work right. The warping causes air leaks which cause high idle and backfiring on acceleration. The attempted fix is overtightening of the screws that hold the top plate to the carb body, which generally makes things worse.
In this situation, the only way to get the car to run right is to find a set of un-warped carbs, or go the Weber route.
I have owned five 250Cs and worked on many others. I have spent a lot of time ajdusting Zeniths and trying to fix their air leaks. I will say that the best running 250 I encountered had Webers.
Falls Church VA