On Tue, 5 May 2009 18:19:31 -0600, "SteveB"
wrote:

Went out to find my low speed jets on an 89 Merc 40. Was shining all over
around in there with a flashlight. Couldn't find them. Saw the plug on top
of the oil injector tank was loose, and went in there to tighten it. Of
course, I only knocked it off, now have to take off the tank to find the
plug which had fallen into the abyss between the tank and the intake
manifold. Which I should have done in the first place to get to the carbs.
As I look over the carbs after I have moved the tank, I notice there are two
holes through the tank specifically aimed at the jet screws. Reachable with
a thin blade long screwdriver.

HAH! Glad it was not a Ford, or I would have probably had to take off the
starter and loosen the motor mounts to do it. So, on the next cruise, I'll
set the jets. Bottomed them out, and came out 1 1/2 turns for now.
Adjusted a couple of hoses that had kinks in them from being cut too long.

Hope to take it out this weekend.

Let us know how that adjustment works out. Personally, I've never had
any luck with carb idle jet screws, 2 or 4 barrel, Carter, Holley or
Rochester.
In my experience they come adjusted to the correct turnout from the
factory or rebuilder, so when you bottom them and turn them out the
correct turns you're back where you started.
And I don't recall any other adjustment being better than that.
Then you've got the throttle idle screw itself to tinker with, which
affects RPM and ear test.
I have had some engines idle better with the screws further out than
spec, but then you're risking washing the cylinders with a over rich
mixture.
IMO without an exhaust gas analyser idle jet screws are a losing
battle.
I'm glad I've tinkered with my last carb long ago.
Geez, I remember in '76 I could get rebuilt 2-bbl Rochester for 25
bucks, a quad for 50. By '90 I couldn't find a Rochester quadrajet
for my 350ci for less than about 400 bucks.
I settled for tinkering and a minor gallop.
Balancing dual carbs is an even bigger PITA. You really need air flow
meters. But maybe I'm just too "perfectionist" and carbed engines
don't allow for that.

--Vic