@bosswrench posted:There is also a split 8-stack Weber intake that uses a valley cover. They're sensitive to throttle linkage routing, whether carbed or EFI. One friend had EFI on such an intake pair and it was subject to idle creep when hot. The cold idle was 900 rpm but when it warmed up, the idle always crept up to about 1200 rpm.
On a dyno, someone finally found that the two banks of EFI throttle bodies were linked by rods, heims and a bellcrank in the valley. With aluminum heads when hot, the two heads (and intakes) expanded away from each other enough to pull on the linking rod connections, which increased the idle by about 300 more rpms.
He had to figure out a different method of linking the two sets of throttle bodies using cables..I think the original linkage would have done the same with carbs, on those heads. Iron heads apparently don't expand that much. An aluminum block would likely be worse. Fun with 8-stacks....
I've had that problem as well on my first run at the Webers. I've also heard this mentioned before BUT I have come to the conclusion that it isn't the heat expansion that causes it.
What happens is that you have to find where the linkage is "zeroed". This takes a bit of experience and if you are building your own first linkages, at least three or four variations before you find the one that lets the carbs return to zero on a hot engine.
One of the things overlooked to a good extent is that the carbs or efi tend to act as heat sinks. When you shut the engine off it rises up first just to boil and percolate the fuel out of the bowls all over the engine and often down into the intake runners.
You can't just use the paper gaskets supplied with the carbs or the o-rings with the efi's, you MUST use the thick asbestos gaskets which reduce the heat rising (not all because of the carb studs transfer some) but also prevent the carbs from walking on the manifold pushing on the linkages.
This isn't a simple thing to do and if you are even a bit schizophrentic tending your mind will run wild with conspiracy theories and you will just slip helplessly into psychotic episodes which will preclude you from further dabbling in Webers or the like.
This was all seemingly proprietary information when I decided to take the plunge in the late '70s on this. The only help there was, was Jim Inglese and he was in the learning lane as well.