Merc 9.8 hp - rough idle

[dajohnson53]

Hi: I posted earlier about a '74 Merc 110 (9.8 hp) that I recently acquired. The thing starts and runs tolerably well, just a little rough. My previous post mentioned that partly for this reason, and partly "for the fun of it", I was going to rebuild the carb. Probably will, but...<br /><br />I'm wondering a little about trouble shooting sequence for a rough idle. Here's what I've done:<br /><br />Checked compression - 125 both cylinders<br />De-carbed using spray method<br />Fresh plugs (plugs that came with it were not the right type; changed to spec'd plugs and it helped a little).<br />Fresh fuel, mixed correctly<br />Cleaned little fuel filter screen that is mounted on carb. Had quite a bit of crud on it.<br /><br />Fiddled with carb. idle adjustment. My understanding is that this is the rich/lean adjustment for idle - out for rich, in for lean, find spot between the "in" and "out" points at which idle gets worse.<br /><br />The idle adjusment doesn't seem to do anything - it might improve idle a *little* at full-in, but there is absolutely no effect at any other setting.<br /><br />The idle in neutral is rough, and I need to keep the rpms fairly high or it will kill. It's hard to shift into gear without killing.<br /><br />In gear, the idle is worse in the sense that it won't even go as low as when in neutral without quitting. At a little higher RPMS (like trolling speed), it will idle all day OK, but kind of rough.<br /><br />There is no overt cough or sneeze or miss, but the idle is rough and the motor shakes quite a bit.<br /><br />I'm wondering if the carb rebuild/cleaning is next or if there are other things I should look at like ignition parts or timing? I know the basics of how a small engine works and have a factory shop manual, but I'm not real experienced at it.<br /><br />Thanks, as usual.