Been having some trouble with my engine for a while now and it seems to be getting worse. My engine runs strong and feels plenty powerful all the way up to about 5,000 rpm. Once I get into this rpm range it will always either just loose power, or start stumbling and after-firing. I generally tend to shift into second if it just loses power but if it starts after-firing I usually panic and let off the gas.
I've noticed from day-one that the needle in my vacuum gauge fluctuates like crazy at idle. The needle quickly dances back and forth over about a 1 inch range. As I understand it, that usually indicates a worn valve guide.
Also, last Fall I had a problem with a sticky lifter. The valve train would start ticking like crazy every now and then for about thirty seconds at a time and then would go away. I ran some Seafoam through the oil and that seemed to fix it, haven't had the problem since. But ever since them my idle vacuum seems to be lower than it used to be, idles at about 12" of vacuum when in gear, used to idle at 15"-16". Also, it seems to be breaking up more at 5,000 rpm and after-firing more often than it used to, almost every single time now. I thought this could possibly have something to do with winter-mix gasoline but it's summer now and I've seen no improvement.
My theory is this: Is it possible that the sticky lifter slapped the valve train around enough to have accelerated the wear in an already bad valve guide? I'm wondering if my valve is not seating properly at higher rpm's.
Here's some specific info on my build, it's a mostly stock 400ci with the exception of the following:
Performer RPM manifold
Road Demon 725 carb
K&N X-Stream filter assembly
Full-length headers
Summit Racing brand cam: 0.442/214 Intake, 0.465/224 Exhaust
Full MSD ingition
14* initial, 38* total timing
Running 87 octane pump gas
No idea on compression but stock compression on these engines can be as low as 7.8:1
Also no idea on the valve springs, I'm going to guess that their stock
Thanks for any help in chasing this problem down. I'm happy to provide any more info that could be in helpful figuring this out.
I've noticed from day-one that the needle in my vacuum gauge fluctuates like crazy at idle. The needle quickly dances back and forth over about a 1 inch range. As I understand it, that usually indicates a worn valve guide.
Also, last Fall I had a problem with a sticky lifter. The valve train would start ticking like crazy every now and then for about thirty seconds at a time and then would go away. I ran some Seafoam through the oil and that seemed to fix it, haven't had the problem since. But ever since them my idle vacuum seems to be lower than it used to be, idles at about 12" of vacuum when in gear, used to idle at 15"-16". Also, it seems to be breaking up more at 5,000 rpm and after-firing more often than it used to, almost every single time now. I thought this could possibly have something to do with winter-mix gasoline but it's summer now and I've seen no improvement.
My theory is this: Is it possible that the sticky lifter slapped the valve train around enough to have accelerated the wear in an already bad valve guide? I'm wondering if my valve is not seating properly at higher rpm's.
Here's some specific info on my build, it's a mostly stock 400ci with the exception of the following:
Performer RPM manifold
Road Demon 725 carb
K&N X-Stream filter assembly
Full-length headers
Summit Racing brand cam: 0.442/214 Intake, 0.465/224 Exhaust
Full MSD ingition
14* initial, 38* total timing
Running 87 octane pump gas
No idea on compression but stock compression on these engines can be as low as 7.8:1
Also no idea on the valve springs, I'm going to guess that their stock
Thanks for any help in chasing this problem down. I'm happy to provide any more info that could be in helpful figuring this out.
