Chevrolet Repair: 454 timing, chev 454, google search

Question
I want to set the timing for a 1987 chev 454 in a motorhome. I live in colorado and I want to know what you recomend I set it to. Also are there any vacume hoses ect. I need to disconnect while setting it. The timing mark on the pully is vertually impossible to see from the top of the engine (class a type motorhome) and I was wondering if it could be done from the bottom of the pully.If you have any suggestions I would appreciate any advice. Right now the engine wants to diesel when you shut it down.            thanks Dale

Answer
Hello Dale,
The dieseling is from hot deposits inside the combustion chamber, and the idle set too high.
They used a lot of things to try to do away with the dieseling.
One is the electric fast idle solenoid, intended to maintain a good idle while the ignition is on, but then drops the throttle plates closed when ignition is cut.
Removing the carbon or ash deposits also helps.
Do a Google search for "water decarbonization", or Sea Foam.
And check the cooling system to see if it is running hotter than it should.

To time it, disconnect the vacuum advance hose, and plug the vacuum source.

From underneath would be possible. First get the timing marks down where you can see them, and use a piece of masking tape stuck on the damper, and copy some of the marks...TDC or "O", and a few others...maybe 5 and 10 degrees.
Then take the tape off and save it.
Then some way or another, get where you can see the regular timing mark pointer, and line "O" up with the pointer.
While it is there, get back underneath, and fabricate some kind of pointer, like a welding rod sharpened, and clamped to some part of the engine so it is close to the damper, and easy to see.
Then stick the tape on the damper, aligning the "O" with the new pointer. Or just use the tape to make some chalk marks on the damper. Be sure to use the tape in the same direction as you made it.

As to what to set it to, I don't know. You might ask a mechanic in that area.
I would probably check it, and then just make small changes till it runs good.

There is also a magnetic timing mark and probe holder if you have access to a magnetic timing light.

Van