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October 9 2017 at 10:40 AM
Dan  (Login 32bantam)

Response to Any horror, or good, stories about 8 stack injection

Hey John,

What system/engine do you have? Is this a modern EFI unit or a mechanical set-up put on a crate engine? Either way it is very common on those units I've worked on to not have the butterflies sync'd properly. It is also common that shaft rotation is wrong so one side doesn't seat correctly. Many units are opposed shaft rotation for equal flow per bank but it is common to see them assembled where the butterflies on each bank park on the same side and rotate parallel to each other. If the casting isn't machined for this the backward side bleeds more air at idle and doesn't brake fully on release. Then the way the air enters the port affects fuel distribution through the range so that side often runs lean. Some units use an under/over linkage for the opposed opening shafts which means you can set them for opening rate or opening distance but not both at the same time. Generally not a huge issue on a drag car but still not equal at all times and a compounding problem on a roadrace or street setup. Others use a jackshaft system that solves this but it can suffer similar issues if split shafts are used. Think motorcycle carbs where they are linked together with a single drive but must be indexed. I've found this to be the problem on several units as the idea is to install the intake and then set each shaft after torquing the manifold while making sure the intake bores are still parallel. Due to this they are often not shipped set-up, the installer just cranks the intake down which binds the shafts and butterflies resulting in premature wear creating more leakage and inconsistent operation. Yet it is most common that the links are simply not adjusted or even worked loose.

I'm not sure if this pertains to your problem but linkage and adjustment is where I start and it seems the last place the shops before me look usually blaming the electronics, barrel valve, nozzles etc.

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