Gasoline - 90 Octane, Ethanol Free (89), or additives, How to reduce valve knock Options

[dcecc1968]

We are having some Spring weather this week in Charlotte, NC (and no rain!) so I've been driving the 914 and noticed that after about 20 minutes of driving, the valves intermittently knock from "normal" to very loud for no apparent rhyme or reason.

Outside of the obvious that it may be time for a valve adjustment, I wondered what Gasoline grade folks are using.

What Petro are you using in your 914?

[dcecc1968]

Thanks for your suggestions. I will definitely check the timing on the engine. Little is known about the engine historically other than I've been driving it for 4 years. Was told it was a 1.8L when purchased, but the stamped engine code says it should be a 1.7L.

The engine knock sometimes is more like a rattle/clatter.

I'm running dual weber carbs IDF40's with the air mixture screws @ 1.5 turns out. I didn't think of the engine running lean... that may be part of the problem.

[wndsrfr]

Thanks for your suggestions. I will definitely check the timing on the engine. Little is known about the engine historically other than I've been driving it for 4 years. Was told it was a 1.8L when purchased, but the stamped engine code says it should be a 1.7L.

The engine knock sometimes is more like a rattle/clatter.

I'm running dual weber carbs IDF40's with the air mixture screws @ 1.5 turns out. I didn't think of the engine running lean... that may be part of the problem.

If it's a 1.7 I would use 92 or 93 octane....it's a higher compression ratio engine.