2f Idle help (1 Viewer)

Chad717

SILVER Star
Joined
Jul 26, 2017
Messages
242
Location
Castle Rock, CO
when I was struggling to get my truck through emissions this fall I set my idle a little high, around 950 rpm, and I hadn't really gotten a chance to set it back down to 650, so I went in and started the lean drop method again after checking the timing. I am using the tach on my timing light and it moves around a bit, so it is kind of hard to do. I am also using a vacuum gauge, but I started to get a little movement of the needle when it is idling that low. I'll post the videos below and I guess my question is how much movement in the vacuum needle is ok. I had always read that it should be pretty steady, but I'm having a hard time fine tuning idle at 650. Here are the relevant specs:

Rebuilt motor with about 500 miles on it.
Just recently adjusted the valves cold, but planning on giving it another go
The cam is not stock, it is a very mild cam that the shop recommended
I'm at 6500 feet elevation, so I think my readings of around 17-18 on the vacuum gauge are pretty good
I can't find any vacuum leaks as of yet.
Vacuum taken off the brake booster


Here is the vacuum at 850 rpm.

Here is the Idle on my tach around 650 rpm.
 

Chad717

SILVER Star
Joined
Jul 26, 2017
Messages
242
Location
Castle Rock, CO
Also some of that clicking you hear in the video with the timing tach is the bad check valve from the ABV to the exhaust. It sounds bad, but I've got a new one on order..
 

OSS

Joined
Jun 30, 2017
Messages
3,283
Location
Oblivion
The idle mixture screw shouldn't be used to set the idle speed. Use the idle speed adjusting screw. Now that you've messed with the mixture screw, your next smog test might fail. A slight repetitive hiccup of the vacuum gauge is normal at lower RPMs.
Even a brand new 2F isn't very happy idling at 650 RPM. Especially when hot. Especially when cold. I'd set it to at least 750.
 

Chad717

SILVER Star
Joined
Jul 26, 2017
Messages
242
Location
Castle Rock, CO
Thanks @OSS. Good info as always. It also makes me feel better! And to clarify, I was using the idle speed adjusting screw to set idle speed.

Since I was working on it, I thought I would lean drop it using the FSM method to make sure it was still good. So I used the idle speed screw to set it to 690 and then used the idle mixture screw to get highest rpm and vacuum. Once I did that a couple times I then set the idle speed to 650. But the 750 sounds like a good plan, it seems much happier there.
 

Chad717

SILVER Star
Joined
Jul 26, 2017
Messages
242
Location
Castle Rock, CO
I did notice today that two of my carb screws that hold the top of the carb on had vibrated loose. I’m gonna take the air cleaner off and make sure they are all tight, probably readjust the valves, make sure I didn’t mess up the idle mixture to much and go from there.
 

Users who are viewing this thread

Top Bottom