You might be pulling in air, leaning out the mixture. With an engine this
old, if it's been run a lot, I'd suggest you check for any play in the crank
and/or replace the crank seals, look for any other possible area for an air
leak.
LD

"lybarra" wrote in message
...
I have a 1970 Mercury 800 80hp outboard motor I've been working on. It
starts great but once warmed up, it has a rough idle and I can't seem to
bring the idle down. We did everything the service manual said and can't
get the idle right. We set the timing, check the fuel fitlers, adjusted
all
the screws. Does anyone have a clue what we are doing wrong?

Thanks