Surge at idle when warm

[Vulcan]

So I installed my Audiovox CC system. I used a vacuum reservoir as suggested in the install guide on the internet for FJRs. I purchased the 1 way check valve for the vacuum line going to the CC unit and reservoir but I got the wrong size (doesn't fit inside my vacuum hose). I ended up just connecting the vacuum line from the #3 cylinder port to a T fitting (1 leg to the vacuum res and the other to the CC unit)Bike runs fine and CC works great....my issue is when the engine is at idle I see the RPM moving up and down 300-400 rpm. Prior to the CC install the idle was very stable when the engine was warmed up. I am wondering if this is because I don't have the check valve installed (I plan to add it but I have not had time to track down one of the correct size yet) or did I knock something around when I was playing under the tank?

Any ideas?

 

[Fred W]

So I installed my Audiovox CC system. I used a vacuum reservoir as suggested in the install guide on the internet for FJRs. I purchased the 1 way check valve for the vacuum line going to the CC unit and reservoir but I got the wrong size (doesn't fit inside my vacuum hose). I ended up just connecting the vacuum line from the #3 cylinder port to a T fitting (1 leg to the vacuum res and the other to the CC unit)Bike runs fine and CC works great....my issue is when the engine is at idle I see the RPM moving up and down 300-400 rpm. Prior to the CC install the idle was very stable when the engine was warmed up. I am wondering if this is because I don't have the check valve installed (I plan to add it but I have not had time to track down one of the correct size yet) or did I knock something around when I was playing under the tank?
Any ideas?

The check valve is only so that the vacuum reservoir doesn't bleed down as fast in low vacuum conditions.

Check for a vacuum leak in the plumbing or vacuum reservoir.

 

[jestal]

You need the check valve, especially if you are going to feed off of just one cylinder. You just added a large accumulator to one cylinder, likely leading to the idle surge. It is acting like a big vaccuum leak in a way. That cylinder can "gulp" from the vac canister causing the RPM to rise. Then, when the "extra" mixture is gone (canister empty, high vaccum) the cylinder drops out causing the RPM to lower. Intake vacuum lowers accordingly. Canister refills with air. Cylinder gulps air. Surge repeats itself. That is why you don't connect large (relatively speaking) vacuum canisters to intake vaccum of one cylinder without a check valve. The check valve holds the vacuum when created preventing the canister vacuum from dropping and the canister refilling itself with air....it interupts the surge cycle. You need the check valve. You want the check valve. Put the frick'in check valve in as described....

Or, it could be a vacuum leak elsewhere......

 

[Timbo2015]

What Jestal said, or just get rid of the canister. Mine works fine without it.

 

[bmwhd]

What Jestal said, or just get rid of the canister. Mine works fine without it.

Go with the check valve. I did the same thing and had the same symptom before putting the check valve in. Put it as close to the tap off the engine as possible.

 

[Shane]

You need the check valve, especially if you are going to feed off of just one cylinder. You just added a large accumulator to one cylinder, likely leading to the idle surge. It is acting like a big vaccuum leak in a way. That cylinder can "gulp" from the vac canister causing the RPM to rise. Then, when the "extra" mixture is gone (canister empty, high vaccum) the cylinder drops out causing the RPM to lower. Intake vacuum lowers accordingly. Canister refills with air. Cylinder gulps air. Surge repeats itself. That is why you don't connect large (relatively speaking) vacuum canisters to intake vaccum of one cylinder without a check valve. The check valve holds the vacuum when created preventing the canister vacuum from dropping and the canister refilling itself with air....it interupts the surge cycle. You need the check valve. You want the check valve. Put the frick'in check valve in as described....

Or, it could be a vacuum leak elsewhere......

Yup!

Shane

 

[Vulcan]

Thanks guys.....I will buy a check valve and see if that fixes things before I go crazy looking for something else.