[BearInTheCorner]

Hi everyone, I have been loving lurking this page for over two years and never actually made an account to create a post.

I have a '91 Sierra and seem to be in the minority of users who doesn't have any issues with their carby. However for some reason the secondary on my Sierra has been disconnected by a previous owner. The vac line has been cut and the hose plugged with a bolt. I don't really want to mess with it as it is running rather well (although it could definitely use a couple more horsepower (the 1800-2500 rpm range is terrible).

Does anyone know why this change would/could have been made to the carby?
I have tried to find info online but most searches just bring up info on how to ensure the secondary is working correctly. I did find a vague post which insinuated that the Sierra ran better with only the primary, but there wasn't much detail as to why.

[fordem]

Let me start by saying I haven't touched an 8v G13 in maybe a decade ...

I can't see the engine running "better" with only one barrel operating, but that might depend on what your idea of better is, if your focus is on fuel economy, then maybe, a single barrel will restrict air flow at the top end, and limit power.

Why - my guess would be the vacuum actuator developed a hole.

[Gwagensteve]

Or the secondary jet was blocked and it fell on its face when the secondary opened?

[BearInTheCorner1]

Both great suggestions, I can't imagine anyone wanting to sacrifice power for fuel economy in an already underpowered engine but I guess anything is possible.

Steve I think your suggestion sounds more likely. In your experience, is it worth investigating getting the secondary working again? (Ie unblocking the jet and reconnecting the vacuum? Am I likely to see a decent benefit? And if so would it only be at higher rpm and high load situations? Or could it give me the boost I am desperately needing when caught on soft sand in the awkward 2nd gear 2-2.5k rpm range? (I have stock transfer at the moment but have ordered 4.16 gears)

[Gwagensteve]

I don't know if my idea is more likely - the idle jet is the smallest. It's unlikely the secondary jet blocked before the primary.

In any case, I can't imagine how bad a Sierra would be to drive with no secondary. You must be a very patient and gentle driver. Yes, you will se an amazing improvement in performance. You're giving up a substantial amount of torque. through the midrange.

[BearInTheCorner1]

Haha it is my first Sierra, I assumed it was just a slug. I will investigate hooking up the secondary and hope that it unleashes some hidden power.