[JLMounce]

For a couple of weeks now I've been noticing that the engine in my 69 bird has not been running the same. I wouldn't say it was running poorly, just not the same.

The idle quality has become rough compared to previously and I've also noticed that at times the clatter that I've always had in the valvetrain will increase, then subside.

At certain times there is a hard thudding gate to the idle as well that you can feel in the car. Almost like one or two cylinders are pumping much harder than the rest.

Yesterday, my suspicions of something going south were confirmed. Had the car out with my My in-laws and my parents and their corvettes. While horsing around a bit, The engine refused to rev past 4000 rpm. I don't let engines do things they don't want to do so I immediately got out of it at that point.

Curiosity got the better of me however and I did a quick bit of testing. Fired up the AFR guage on the FiTech handheld and wanted to verify I wasn't leaning out. At least via this observation method, my fueling is accurate around 12.6:1 at WOT. If I stay in it however I'll get a backfire through the throttle body.

If I nail the throttle the engine stutters badly and then will accelerate. If I roll into the throttle easily it will accelerate, at least up to about 4000 rpm where it falls on it's face. Overall power is down as well and the engine does not sound happy at all beyond 3500 rpm.

I need to put a fuel pressure gauge on the system to verify for sure this isn't fuel related, but I'm about 90% sure I can rule that out.

What I'm currently thinking is that I've got a valvespring or lifter issue, possibly both.

The top end was put into service in mid 2015 and I'd say I have around 30K on it. KRE D-ports with whatever springs Kauffman installed. The cam is a comp roller at 232/238 112+4. It uses the following XFI lobes.

Intake - 13081B
Exhuast - 13141B

.543 and .538 gross lift with 1.5 rockers

I know these lobes are pretty aggressive and were originally designed with intended use of a beehive spring. I have dual cylindrical springs in my setup.

I'm hopeful this can be a spring and lifter change without removing the heads, but I need to get in and do some diagnostics this week.

I'm not sure if weak valve springs will show up on a compression test, but that is first on the list as well as visual inspection of the current valve springs. From there I'll take the intake and valley pan off and start inspecting the lifters and the cam itself.

I'd really love to hear from more of you on anything I might not be thinking about here. I had this engine out of the car last year, inspected everything and visually it was all gravy. Bearings looked fantastic etc. I'm pretty bummed that it's giving me fits currently.