1997 Mercury 15hp two stroke - only runs on choke.

[Soporific]

Basically yes!!! One prime for cool, two for cold and none for warm motor. Then turn to the right until warm then to the left to idle down before shifting. Also can be used to fast troll and catch the big one!!

[staylor]

I've had 3 of these 15's over the years and setting the idle speed/mixture is a bit tricky. Baseline mixture setting for the idle jet is 1 and 1/2 turns out from lightly closed. After this put motor in neutral, have primer pushed in and turned all the way counterclockwise. Next turn idle speed screw out until it is not touching cam follower, then turn in until it just touches follower, then turn in an additional 1/2 turn. if your motor does not have an idle speed screw, then loosen the cam locking screw, press cam follower down until it touches the throttle cam, and re-tighten screw. If the carb is OK, then these settings should get the motor to idle OK with primer off and knob turned full counterclockwise after warming up for a couple of minutes. Assuming you then have an engine that idles with the primer knob turned full counterclockwise, then play with the idle mixture until it runs smooth- I usually turn the mixture screw in until I get a slight lean roll-off, then I open the screw 1/4 turn. Lastly, you should reset the fast idle speed with motor in neutral and throttle handle turned to lowest idle position. The primer assembly has a wire attached to it at the top of the primer linkage arm with a screw adjustment. Tighten this screw to take almost all slack out of the wire.

If the above doesn't give you an engine that idles, then check the assembly of the primer rod and diaphragm. If you bought a carb kit from Merc make sure you have the later model kit with a blue plastic primer rod. The early kits with a white primer rod are missing a little spear-like projection on the bottom of the rod that forces the primer ball off its internal seat. Missing this projection causes the rubber primer diaphragm to force the primer ball off its seat hydraulically- causing leaks over time and an engine that won't idle. Also- many of the repair kits from Merc for motor S/N above 9831800 delete a little gasket that goes under the primer diaphragm. I usually re-use the old gasket since the carb casting where the diaphragm seats is a bit on the rough side- allowing leaks to occur.

The carb Merc uses on the 15's appears to be a Japanese Mikuni carb- as distinct from the older Mercarb used on earlier motors- the Mercarbs were simple and reliable and rarely had much that could act up.
Doug

[staylor]

Two more thoughts:
When you set the idle timing the primer knob must be turned all the way counterclockwise since the knob actually advances the spark thru the control wire at the tip of the fast idle arm. Since your setting to an rpm, the motor must be running at idle speed without the fast idle engaged. If you set with the knob turned to a fast idle position your actual timing with the knob turned full counterclockwise will be retarded quite a bit.

Also- if the exhaust relief ports at the top of the lower unit tower are blocked with carbon the motor will not idle- this is a common problem with this motor if they are used a lot for fishing. Use a drill bit by hand to clean out the carbon. I had one motor that would start on the primer but died whenever you turned the knob down. Simply cleaning out the carbon fixed the problem and the motor ran like a watch.
Doug