View Full Version : rough idle in gear when warm

ski n fly
07-30-2006, 11:55 PM
Have a 87 Prostar190 with a holley 4 barrel carb. The carb is fairly new and we operate at 6000' msl. The boat will idle in gear great and run at high rpm also very well untill the boat is 'warmed up" ( after one pass/set). Then when in idle and in gear, the boat will run rough and cut out/ engine will quit. The plugs are all clean and have electronic ignition. All temp and pressure guages read normal. PLEASE HELP...ANY SUGGESTIONS............... Bad fuel pump, bad gas, bad water pump, what??????????????

07-31-2006, 10:22 AM
Try adjusting the 2 air/idle screws, 1 each side, behind the front bowls. Turn screw all the way in till it stops and quickly back out somewhere around 1 1/2 turns, slightly adjust in or out till engine runs smooth at idle when warm, hopefully this helps. I usually adjust once a year just to keep it smooth running when at idle. Also, adjust idle speed screw in port side of carb near linkage/with spring behind it, to 600 RPM at idle in gear.

07-31-2006, 02:04 PM
is this a new problem ? boat ran fine at this elevation last summer ?
it sounds like it runs fine at fast idle [engine warm up] and runs lousy at idle when warm ? if it ran fine before what has changed since then ?
is it just a new carb ?

I like TMCNo1 idea of setting the idle mixture / throttle speed screws first and see where that takes you.

post more info


07-31-2006, 04:54 PM
Older engines with carbs, need periodic adjustments, unlike the newer engines with computers that do it for you no matter what the elevation, barometric pressure, temperature, humidity, etc.