1996 R1100RT Vacuum specification

Does anyone know what the vacuum specification should be at the throttle body vacuum port? I can't find any reference to it in either of my manuals. Thanks, oldcarman jim

oldcarman said:

Does anyone know what the vacuum specification should be at the throttle body vacuum port? I can't find any reference to it in either of my manuals. Thanks, oldcarman jim

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I don't think there is one. Too many variables. In the old days Chiltons always showed a range of values when using a vacuum guage.

PGlaves said:

I don't think there is one. Too many variables. In the old days Chiltons always showed a range of values when using a vacuum guage.

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Those values were based on multiple cylinders and the gospel for engine diagnosis.

You can get 17 in/hg on our antiques if you tee the hoses on a healthy engine. Those values are irrelevant.

You have to start with a balance, whatever that might be.

Then, go to cruise rpm, me, 4500 rpm and balance.

On an old Chevy, the values had significance. On my new Ford truck, not at all.

I think DY is correct. Balance and not exact figures are what you are after. The throttle bodies are set to a specific flow rate on a "flow bench" set up with the right equipment but I've never seen what the exact spec is. Once set, they paint the adjuster screws with blue paint which should never be cracked or adjusted unless you need to replace the throttle shaft and have to do it.

When rebuilding, you eyeball the throttle plates and center them as per the instructions and use Roger04RT's method using the TPS voltage to set the left side to the correct opening at idle mechanically. Then you balance the right one using a vacuum sync tool to match the left one exactly and go from there with your throttle sync.

My bike was purchased last year with only 10,000 on it. It had done a lot of sitting over the years but still ran pretty nice when I got it. I just finished setting my valve lifter clearances and synced the throttle bodies. Prior to that I also removed the throttle bodies, cleaned them with carb clean, very dirty and sooty. Removed the fuel injectors and cleaned them, removed the idle screws and cleaned them. Just for reference my numbers are as follows. Warmed engine, at idle, about 1,100 rpm, vacuum on each side is about 7 in. Both brass screws set to 1 1/2 turns out. At 3,000 rpm vacuum is about 8 in on each side.

oldcarman said:

My bike was purchased last year with only 10,000 on it. It had done a lot of sitting over the years but still ran pretty nice when I got it. I just finished setting my valve lifter clearances and synced the throttle bodies. Prior to that I also removed the throttle bodies, cleaned them with carb clean, very dirty and sooty. Removed the fuel injectors and cleaned them, removed the idle screws and cleaned them. Just for reference my numbers are as follows. Warmed engine, at idle, about 1,100 rpm, vacuum on each side is about 7 in. Both brass screws set to 1 1/2 turns out. At 3,000 rpm vacuum is about 8 in on each side.

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The values have no significance. I look to make my gauges equal at 4500 rpm(cable stretch etc.).

I rarely care that I have balance at idle. I look to where I spend most of my time, 4000-5000.