piston / cylinder question

[Loa]

Hello,

I've removed the heads from my 340 (to machine the valves) and discovered that the piston heads and cylinders were quite blackened (like the bottom of the heads).

Is that normal? Can I or should I clean them? if so, with what?

Thanks

[brads70]

It's normal. Just carbon build up. Might be running a bit rich?  What do the plugs look like?

[dpcd67]

What he said. Your machine shop will clean the heads before they work on them.

[Loa]

The plugs are black and will be changed.

Since I only saw the pistons because we're changing the cam, lifters, redoing the valves and rebuilding the carb, I don't think I can really adjust anything right now...  :-)

I know my carb is too big, a Holley 780. It was already on the engine when I bought it last summer, and I'm planning to change it when I find the cash.

[Chryco Psycho]

set properly a 780 is really not overly large for a 340 , the factory used 800 cfm thermoquads

[Loa]

Nice, and good to know!

Any tips on how I could set it up? The jets are 70 right now. Should I change them?

Loa

[Strawdawg]

Nice, and good to know!

Any tips on how I could set it up? The jets are 70 right now. Should I change them?

Loa

they are probably close...looking at plug color after a wide open throttle run is the tried and proven method.  today, if we buy one, we can use a wide band O2 sensor for tuning a/f but there will not be a significant change in the hands of an experienced tuner that looked at the plugs...

[Chryco Psycho]

in the Archive section there is a basic Holley tuning guide , you need to work through that in order , or every change will affect another circuit , work through that I will can help if you have issues

[Loa]

Found it, will read and apply!

Wow! That is a lot of steps! Glad to have found the guide.

Loa