350 chevy timing

[jonsblacks101981]

i was wandering if u guys could tell me what problem i have 79 350 mild cam hei
initial timing is set 10 or 12 it starts up good but when i turn it off it tries to start back any help appreciated thanks

[stripe]

hot spots in the cylinder head from casting leftovers or carbon build up can cause dieseling. low octane fuel in a high compression motor will do it too. the problem is compounded by the ethanol (evaporates quickly and can ignite in a hot cylinder) that's in today's fuel.
Of course, these all assume there's fuel in the cylinder to burn... if there is, it's probably too rich.

[adh383]

You mean it wants to keep running when you turn it off? Back timing off till it will stop when you turn it off-- also look for vacuum leaks.

[harleyboy]

You mean it wants to keep running when you turn it off? Back timing off till it will stop when you turn it off-- also look for vacuum leaks.

thats about right on the money.

[Scotty_S-15]

Presuming we're talking about engine run-on.........
My first thought would be vacuum leak too. (is there an echo in here?):icon_lol:
Another clue to this is that when starting the engine up, you might have needed to shut down the carb throttle plates (idle speed) to keep it from racing.

Could be something as simple as a hose off, pipe plug out, or wrong/damaged carb gasket.
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[jonsblacks101981]

i dont think its a vacumm leak because i can control curb idle speed might be low grade fuel because i have been running 87 octane it has 10.5.1 compression ratio is 12 degrees intial timing to much

[littlewickeds10]

you running iron heads or aluminum heads? i'd almost guarentee 10.5:1 compression and 87 octane is the culprit....

[coppergmc]

Try a cooler thermostat, use a cooler plug, try better gas, and back the timing down in 2* steps until it stops running on. I'd probably start by checking my timing. Make sure that anything that might advance the timing is the way it is supposed to be. See if unplugging the vacuum advance helps while you are at it.