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Discussion Starter · #1 ·
Just wondering what are all the vacuum lines on the throttle bodies for? Recently cracked one of the plastic fittings on accident and im pretty sure its caused a vacuum leak, was considering blocking off the hoses and leaving it but decided ill just replace the fitting instead. Anyone know what all those hoses are for? What would happen if you just removed them and blocked off the nipples that they attach to?
 

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2nd-Gen machine assume? They're critically important. Each throttle body generates vacuum and there are four independent throttle bodies.

The vacuum they generate is used to attenuate fuel-return by the fuel pressure regulator. Unplug the vacuum line and the pressure regulator won't return the fuel that it normally does at idle and part-throttle operation.

They also pull vacuum against the Intake Air Pressure sensor; used to calculate MAP for the fuel injection system.

Visit the hardware store and get three feet of vacuum line. Make sure they don't hand you washer fluid line, like they did me. Though it looks the same, it won't stand up to the heat of an engine bay; it'll collapse under vacuum. Washer fluid line may say "1 bar" or similar on the hose.

Photograph your assembly. Cut up the hose in sections that match the lengths in your original. Use those new sections to replace the degraded sections of your original.

My hoses visually looked fine. It was code 20 that led me into replacing them. More information here...

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Discussion Starter · #3 ·
2nd-Gen machine assume? They're critically important. Each throttle body generates vacuum and there are four independent throttle bodies.

The vacuum they generate is used to attenuate fuel-return by the fuel pressure regulator. Unplug the vacuum line and the pressure regulator won't return the fuel that it normally does at idle and part-throttle operation.

They also pull vacuum against the Intake Air Pressure sensor; used to calculate MAP for the fuel injection system.

Visit the hardware store and get three feet of vacuum line. Make sure they don't hand you washer fluid line, like they did me. Though it looks the same, it won't stand up to the heat of an engine bay; it'll collapse under vacuum. Washer fluid line may say "1 bar" or similar on the hose.

Photograph your assembly. Cut up the hose in sections that match the lengths in your original. Use those new sections to replace the degraded sections of your original.

My hoses visually looked fine. It was code 20 that led me into replacing them. More information here...

View attachment 378172
Thanks, I was just really curious what they were for. I actually have the hose unplugged from the fuel pressure regulator since it increases the fuel pressure which I needed since I have homemade slide stops and don’t have a fuel pressure booster. I originally just had the hose plugged off but accidentally cracked the fitting that the pressure regulator hose would be hooked up to. Turns out I actually have a spare one of those fittings off a set of throttle bodies for a 08 r1, and it doesn’t have the nipple for the fuel pressure regulator hose which is actually perfect for what I’m using it for. I’ll put a picture of the part I cracked, and the one off a r1 that I’ll be using instead.
 

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Auto parts stores carry vacuum tee sets; they can be used to reconstruct missing or broken parts. You may need some caps to go along with them.
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Not sure what you mean by "homemake slide stops" ? Are you referring to the sliders for the auto-choke system?
 

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Discussion Starter · #5 ·

Auto parts stores carry vacuum tee sets; they can be used to reconstruct missing or broken parts. You may need some caps to go along with them.
View attachment 378175


Not sure what you mean by "homemake slide stops" ? Are you referring to the sliders for the auto-choke system?
No, slide stops just hold the vacuum slides wide open for increased throttle response. I didn’t feel like buying the graves slide stop kit just incase I ended up not liking them so I just made them myself out of some pvc, does the exact same thing only downside was that I didn’t have the fuel pressure booster that usually comes with the kit, then after doing some research I found out that u can increase the fuel pressure by just unplugging the vacuum hose from the regulator and plugging off the hose, which is what I did.
 

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Oh those. Okay the black slides are called "Throttle Valves" and the rubber bladder or boots are called "Diaphrams".

I forgot about those and you're right, those are also operated by vacuum.
 

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I forgot about those and you're right, those are also operated by vacuum.
Something that is interesting, idle has high vacuum only because the throttle plate is closed. That vacuum disappears as the throttle plate is opened and before the engine (air pump) has a chance to catch up.

But you don't want these throttle valves open at idle (high vacuum) and closed at WOT (low vacuum).

So they're vacuum operated but must be sucked open at a time when vacuum is lower.

I suspect they're sucked open, only by rapidly moving air.
 
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