250f is fine. 300f is pushing it a bit!

I stopped using temp guns years ago. I only tune with spit now, as it is always consistant.

If you dab a drop of spit to the cooling head and it stays there and slowly evaporates then you are too cold. If it quickly jumps off the head then you are generally too hot. You want the spit to sizzle for about 1-2 seconds then dissapear to be within a safe range.

More important in my opinion is to remove the head button regularly and view the combustion color on the head button and piston crown. This gives you a much better idea as to whats going on inside the engine. Also you will get quick warnings to dangerous running conditions such as detonation and lean conditions.

Also look for slight wetness to the piston top. Too much oil and your too rich, and dry piston you are too lean.

Constantly removing the head button will also give you the opportunity to readjust the head clearance with shims, which is one of the most important tuning adjustments with these engines for all out performance. Just take care to always seat the head correctly and tighten evenly. And lastly, don't overtighten the head screws or you can deform the block putting pressure on the piston sleeve. This will cause pressure points and you WILL loose power and destroy your piston/sleeve set.

Just my 50cents worth!

BK