High throttle miss

[olddog]

Originally Posted by Texasdoc

One thought previously mentioned was a failing spring causing valve float. I've looked at the springs, even rolled the motor over a few times with the starter while the valve covers were off. I have a spring compressor coming from summit so I can disassemble the valve train to closer inspect the springs. Will a damaged but not broken spring be readily apparent or is there an easy way to test them?

As mentioned you can measure the spring pressure. I was thinking more in the line of a broken spring, which you could visually see. This is assuming that the engine at one time ran perfect and this is a new sudden problem.

As I said I did not read the thread so you may have already ruled out things and you may have already explained things that I do not know.

If I removed a spring, I would run the piston to TDC and measure the valve clearance with the piston, especially if this is an engine you never saw run correctly. A valve lightly kissing a piston at high rpm may give strange results.

The valve spring and clearance may not be the issue, but I didn't want you to over look it because these can totally kill an engine.

On the ignition miss list, I had an issue that on hot days my engine would break up bad. I sounded like someone was turning the key off and on rapidly. In the beginning, it might do it once and not again for another year. It took me 4-5 years to track it down, because it would never do it when I had any tools to troubleshoot with me, and I could not make it do it. In the end, it was the ignition key switch. Yes someone was turning the key off and on rapidly. My dangling key chain.

Good luck