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At the sand dunes (Gordon Wells), I get a noise, that sounds like pinging/rattling noise at 1/4-1/2 throttle just as it transitions into the power band. Happens both in deep sand, and on the harder flats. Any thoughts? Is this detonation, or is this awful sound typical and O.K.?

I am running PWK bored to 40 mm. DGL middle clip.

If you're running pump gas, run race or av gas, the higher octane should clear it up if that ie what it is.
on the other hand you mentioned 1/4 -1/2 throttle, if you are just crusing with a paddle tire the chain can make a lot of noise.

maddog1927 wrote: Is this detonation.

Yes, and its not ok. Increase octane as instructed, or you can raise the needle to let more fuel in at part throttle and see if that helps.

You have to stop it, or damage will occur.

Running av gas. I'll try raising the needle. What needle has the 1.5 taper Bob suggests for duners?

AV gas sucks...... Raise the needle tell it stops pinging. If you run out of slots go to DGK needle.

What fuel do you recommend for duners? Anyone like running u4? I used to like u2, but no longer available..

I'd say richen the L portion of that needle. DGK like Paul says.

I just run 91 pump gas 50:1 and maybe some Octain boost if I'm out there with you guys. But have found the boost not nessessary.

Av gas is just that. Gas for flying a plane. Has antifreeze in it for altitude temp drops. Leave it for the Cessnas. I run a 50/50 mix of 93 and Klotz 110, because the distributor is 10 miles away from my house. VP C12 would work too.

Isn't it better to lower compression instead of running too fat?