Mercury 50 hp, 4 cyl, 1984 Model, Idle problem

I just had carbs rebuilt by the dealer as well as installed and adjusted by them. The motor will not idle worth a darn, so I called the dealer and they told me to take the water separator out of line. They said the resistance it caused was to much for the fuel pump to pull. Well I did that and it still will not idle. Runs beautiful at mid-high range, but do not try to idle it down. Compression is 130 PSI on all 4 cyl, stator is good and has a new trigger installed. The fuel line is new and the ball pumps till hard. I can keep it at idle if I choke it every 5 seconds and when I do that the RPM's go up till it starts to stall again. What is being missed here? Any ideas out there on how solve this? The dealer says it runs perfect in his shop and it must be my fuel, which it is not. Is the carbs not adjusted correct? I am going to bring it back to him Wednesday for review but I need more ideas.

HELP!!!!!

Dave

Definetly sounds like something was " missed " in the carburetor/s.------Try opening the low speed jet 1/8 turn at a time and one carburetor at a time.------If running / idling improves you will know which carburetor was at fault and also which cylinders had the problem ( 1 and 2 or 3 and 4 )------------Sometimes they run quite nice with no load and no backpressure on a hose and then stumble when submerged and trying to turn a prop in the water.----------------There may be other internal problems with crankcase compression ( leakage ) that are harder to diagnose for sure.

What is the mechanism for the crankcase being the problem if the Compression is good? Also how is a crankcase pressure problem resolved and addressed? Thanks for your help.

Dave

What he means is a bad crank seal or ?? that might be lousing up your idle. It sounds to me that your motor simply needs a better idle adjustment, and that you need to do first.

Try this: Leave the boat on the trailer or tie it to the dock. Warm the engine thoroughly, in gear, keeping it running anyway you can. Then idle it down as much as you can without it stalling. Next, turn one idle adjustment at a time in and out until it runs better. Finally, when you have the best adjustment you can get, open both out (CCW) 1/8th of a turn (45 degrees).

Jeff

Davio---------------Your motor is a " 2 stage air processing machine "---------------A sealed crankcase will draw in air mixed with fuel.----------------It is then compressed in the crankcase and transferred to the cylinder.--------------------When exhaust ports close that new mixture is compressed in the cylinder and ignited.----------------------So you need both on your motor , good sealed crankcases and crankcase compression. and good cylinder compression.---------------------You can have good cylinder compression and no crankcase compression on the same cylinder.--------Confusing perhaps but that is the way it is.

racerone said:

Davio---------------Your motor is a " 2 stage air processing machine "---------------A sealed crankcase will draw in air mixed with fuel.----------------It is then compressed in the crankcase and transferred to the cylinder.--------------------When exhaust ports close that new mixture is compressed in the cylinder and ignited.----------------------So you need both on your motor , good sealed crankcases and crankcase compression. and good cylinder compression.---------------------You can have good cylinder compression and no crankcase compression on the same cylinder.--------Confusing perhaps but that is the way it is.

Click to expand...

I will talk to the dealer about this Wednesday morning. Thanks racerone and I will let you all know.

Dave

Well here's the deal. Took it to the dealer and fired it up with the muffs. Had a bit of a stumble to fire up, but with advancing the throttle and light choke it fired up. After warming up at at a high RPM the motor was bought down to idle. It was on the verge of stalling and the tech then adjusted the set-screw idle (mechanical stop) on the port side of the motor. He did not adjust the carbs at all. This bought the RPM up enough so the motor would not stall. I brought it home and fired it up. It still had a hard time idling down so I adjusted the RPM up a little higher and it performed nicely. The tech dismissed the notion of the crank-case vacuum being to low. I hope that I can now enjoy some time on the water.

Any feedback will be welcome.
Thanks,

Dave