[Malibujoel]

Hi all.
I have a 66’ Mustang with a 289. Motor was built in the 80’s and now in my 66’. Car that motor was in the 80’s got hit so I pulled motor out and it’s been sitting in garage ever since, till now. Put new seals on motor and upgraded the carb to a Edelbrock AVS 2 and a HEI distributor.
Problem I ran into is when car is warmed up it idles at 1250 rpm. Put C4 auto in gear and idle drops to 350-420rpm.
New gas tank. I checked compression and most cylinders were at 120-125psi. #1 and #8 were at 90psi. So I took another round of compression readings and a few of the 120psi now dropped to 90 psi. My only thoughts are the lifters are failing after sitting in engine 30 years plus.
Any thoughts would be greatly appreciated.
Thank you.

 

[dennis111]

Overheated weak valve springs can do that too.

 

[Malibujoel]

Thank you Dennis.
I did replace all the valve seals. Is it possible to put springs in the wrong direction?

 

[dennis111]

No there are not normally directional (unless they are conical.)

 

[69StangRestomod]

you do have the throttle all the way open when testing right? Having the throttle blades closed can give wacky readings.

 

[Malibujoel]

I did not have throttle plate open all the way. Will retest this morning and repost results. Thank you.

 

[Malibujoel]

Perfect! Thanks again Dennis

 

[Malibujoel]

I took vacuum readings at idle and at 1200 rpm vacuum has a needle fluctuation between 16.5-18. When putting trans in gear idle still drops to 380-420 and vacuum drops to 15. I decided to re-check valve adjustments and push rods were loose at TDC. so I readjusted vale’s and took compression again now number #2 cylnder drop to 60 psi and push rods are a bit loose again at tdc. I believe this to be the lifters to be failing after sitting in engine since the 80’s and not fired up till now. Any input would be greatly appreciated!
Thank you in advance

 

[Malibujoel]

I removed intake manifold this morning and removed both lifters from the #2 cylnder that seem to have the most fluctuations in compression readings. The lifters slid out 2/3 of the way and had to use plyers to get the out as they got stuck at this point. Will replace valve springs like Dennis mentioned and lifters as I’m there already. Do I still need to use break in lube on lifters or just soak them in oil for a couple days and just install? Anything else I should look for at this point?

 

[Malibujoel]

I just took a look at top of valve stems of #2 cylnder were I removed the rockers to get out the lifters. The top of the exhaust valve is mushroomed on a angle. Measured from keepers to top of valve. 0.151”-0.105”. The intake measures from keepers 0.177” all the way around as it’s not mushroomed. I took a visual of the other valves that still have springs on them and there are a few more that are mushroomed at top of valve. Wonder what causes this? I looked at roller rockers and they look and roll ok.