Click and short drop in power at high RPMs - 1969 Mercruiser 120hp 2.5l

[mercruiser1969]

Under high RPMs (>2700), my 1969 Mercruiser 120hp 2.5L makes one relatively loud click followed by a very short drop in power then resumes normal operations. This happens within 1 second. I just installed a new head block, so thought that may have something to do with it. It almost sounds like a valve isn't opening somewhere when it should. This does not happen at lower RPMs at all.

Let me know if you have any ideas.

 

[Bondo]

Ayuh,...... Welcome Aboard,...... I have no idea, not any symptom I've heard of before,......

 

[mercruiser1969]

A couple of folks thought it may be a sticky valve guide on the new head. Recommended Marvel Mystery Oil.

 

[Bondo]

A couple of folks thought it may be a sticky valve guide on the new head. Recommended Marvel Mystery Oil.

Ayuh,..... Generally speakin', a sticky valve only sticks once, then the push rod is bent,....
'n a new head, shouldn't have sticky valve guides,....

The fuel pumps on those motors sometime tick as the lever rides on the cam,..... donno,......

 

[kenny nunez]

Did you use new valve springs and /or the valves are slightly too tight .

 

[mercruiser1969]

Realizing it’s more of a puff of air at high speeds. Thinking it’s something either in the fuel pump or the filter/line causing the sound.