Mercury 165 Idle issues

[jamnajar]

I have been fighting a low hour Mercury 165 (mid 70s boat/engine/outdrive) for a bit now. I feel like I have read every thread I can find regarding 'Low Idle' and 'staling going into gear'.

Root issue: Rough idle, Boat dies while trying to put it in gear (in the water). If we do get it into gear and it is still running it will stumble then die. It also does not idle like it should when out of the water on ear-muffs. (sounds like a miss? Sometimes if I just let it idle out of gear (on ear muffs) it will idle for a bit (15 seconds?) then will stall. But it is intermittent!

Parts recently replaced:
Fuel pump (with a fancy new marine one with the 3rd barb)
Rebuilt the original Rochester Carb (which looked brand new inside) cleaned out the in-carb filter. Set back to factory specs.
New Cap + Wires + Spark plugs (all from legit marine store)
Bought 'Hot Spark' ignition module and coil. Ended up taking the drop in out and going back to points (verified 12 volts on the coil, and still wouldn't run worth a dang, sounded like it was running on one cylinder! Figured I got a bum drop in, or the wrong magnets)
Verified timing at 6' BTDC

Warm compression test showed all cylinders between 115 and 120psi. When I pulled the plugs they all looked decent (light brown on the center insulator, proper gap etc)

Also noted: right as it is stalling i hear the carb sucking air (like when you slam it WOT) but the throttle is closed.

Thanks in advance! This forum has saved me so many times!

What should I check next? Valves?

 

[Grub54891]

Re: Mercury 165 Idle issues

I would do a compression test and post the results.Warm the ,motor,check it, add a teaspoon of oil and check again. You could do a leakdown test also to really see where the motor is at. If it dont sound right is must not be! Let us know how it goes. Grub

Did you check the rest of the fuel systym? check for any blockage all the way through the systym.

 

[mrlassi1]

Re: Mercury 165 Idle issues

Look for an intake manifold leak or a faulty ignition coil. Consider an electronic ignition module, I'm not familiar with "hot spark", but had success with a model called "Petronix Ignitor". You must have the red lead to the electronic ignition module wired so that it sees the proper resistance through the coil.

Good luck!

 

[Silvertip]

Re: Mercury 165 Idle issues

Choke operating properly? How did you clean the internal fuel filter? They are either sintered bro9nze or a pleated paper element. Either one should be replaced. Did you get the filter installed the correct way? If it sounds like it is missing, do you have the idle mixture adjusted properly and are you certain you have the firing order correct? How thorough a job did you do on the internal passages in the carb. Simply washing out the float bowl is not adequate.

 

[Fishermark]

Re: Mercury 165 Idle issues

How's the dwell? See if it fluctuates. Could be a worn distributor bushing.

Have you checked to see if the switch interrupt is engaging when you are shifting into gear? (It shouldn't).

 

[Oshkosh1]

Re: Mercury 165 Idle issues

I would do a compression test and post the results.

Ummm...

Warm compression test showed all cylinders between 115 and 120psi.

Did you check for any obstructions in the exhaust?

 

[jamnajar]

Re: Mercury 165 Idle issues

Thanks for all of the suggestions, you guys are awesome!

When I went through the carb everything looked brand new, I still went through each orifice with carb cleaner and my air compressor. The choke seems to be functioning correctly, (I even closed it to see if it was not being choked enough. I changed all fuel filters except for the one built into the fuel pump. I think I will get a normal barb to replace it, and run a paper filter upstream. I havent checked the dwell. I am debating replacing the condensor + points or just getting a Pertronix (I always ran pertronix in my vintage VWs), I will also double check the wiring to the coil (I did this once and verified 12v but ill check it again) The exhaust seems to flow fine but I'll see if I can find any obstructions.

Q's: is there any decent way to check for fuel blockage from the fuel tank itself? (maybe run a temporary separate fuel tank?)

 

[Fishermark]

Re: Mercury 165 Idle issues

Q's: is there any decent way to check for fuel blockage from the fuel tank itself? (maybe run a temporary separate fuel tank?)

That is the easiest way to verify if the tank or plumbing is the problem. Just get a portable tank diesigned for an outboard and plumb it to your pump. See if the problem goes away.

 

[RenkenII]

Re: Mercury 165 Idle issues

DOn't forget the screen that is in the elbow coming out of the fuel tank. I had a similar issue, cleaned that and I was off. The ethanol is removing any build-up that has been in the tank for years and plugging everything. Relating to that, I also did the carb rebuild and found that mine to be fairly clean. BUt replacement of the accelerator pump and adjusting the float to the proper setting and the boat runs like new. Based on your description, I would say your dealing with a fuel delivery issue as opposed to an electrical issue.

 

[jamnajar]

Re: Mercury 165 Idle issues

DOn't forget the screen that is in the elbow coming out of the fuel tank. Based on your description, I would say your dealing with a fuel delivery issue as opposed to an electrical issue.

I will need to see how I can get at that screen., I will get a separate fuel tank and test that side of the fuel delivery system tomorrow. (I think I have one for a sand rail sitting around) I will post the results. Thanks!

 

[jamnajar]

Re: Mercury 165 Idle issues

SO I tested with another fuel tank and it ended up running better out of the water but in the water it was doing the same thing. THe boat would barely idle while cold, and in gear, would stumble horribly on WOT, and once warm would not idle in gear at all. I had the pleasure of helping row the boat a few thousand yards to the dock =( I noticed that the accelerator pump barely squirts into the throats. That would explain the stutter on hard acceleration but would it effect the idle? I did adjust the valves after we got it back to the house (did it warm method on muffs) I guess the next thing to do will be to pull the carb and check the float height and the accel pump?

 

[888]

Re: Mercury 165 Idle issues

Have you checked to see if the switch interrupt is engaging when you are shifting into gear? (It shouldn't).

Sure sounds like the issue to me too. Works great on trailer but dies in water cause the shift interrupter switch either needs adjusted or replaced. Try this,remove the engine cover next time your out on water and have someone operate the interrupt switch while you drive. The switch activates when u shift gears and sounds like urs is sticking.

 

[jamnajar]

Re: Mercury 165 Idle issues

. The switch activates when u shift gears and sounds like urs is sticking.

I will check that out. Does the switch activate only when you shift out of a gear,(going into neutral) or when you shift into gear? (Going into forward or reverse) Is the switch is on the transom near the end of the shift cable?

 

[jamnajar]

Re: Mercury 165 Idle issues

What I did today: I rebuilt the carb (with a new carb kit), checked the interrupt switch and verified proper operation. (it wasn't sticking). I verified the float drop and height settings, and soaked the accelerator pump before reinstalling, and verified proper choke operation.

I noticed something today: When in neutral and idling (on muffs) if I punched it to WOT then immediately back to idle (as fast as I could) I would stall the engine. In fact when I went WOT fast (never letting the RPMS run away) the engine would sputter (Bog down)for a moment then would pick up RPMS. (still on muffs) I did verify the distributer was at 6' BTDC. Does this sound like the distributor weights are sticking and not advancing fast enough or like there is not enough fuel getting immediately to the pistons?

 

[RenkenII]

Re: Mercury 165 Idle issues

Try getting it into the water and run it for a while. Make sure your gas is good (no water - add some dry gas or Stabile) and just run it at a moderate pace for a while. Allow the carb and motor to warm up good - get the juices flowing per say. I think this may help. It may allow you to evaluate it better also. Just a thought.

 

[jamnajar]

Re: Mercury 165 Idle issues

Try getting it into the water and run it for a while. Make sure your gas is good (no water - add some dry gas or Stabile) and just run it at a moderate pace for a while. Allow the carb and motor to warm up good - get the juices flowing per say. I think this may help. It may allow you to evaluate it better also. Just a thought.

When I did this the previous time my friend and I ended up having to paddle the boat in 1000 yards or so back to the docks. =) The gas is good, (brand new and I am not using the factory fuel tank, I'm still using the one from my sand rail)

 

[mrbuilder11377]

Re: Mercury 165 Idle issues

your intermittent switch is not in the right position I had the exact same problem up untill today take the cowl off look at how the shifter operates and make sure the switch goes in the right positions or replace it if its not in the right position it will lead you to believe you have carb problems fuel pump problems and so on

I have been fighting a low hour Mercury 165 (mid 70s boat/engine/outdrive) for a bit now. I feel like I have read every thread I can find regarding 'Low Idle' and 'staling going into gear'.

Root issue: Rough idle, Boat dies while trying to put it in gear (in the water). If we do get it into gear and it is still running it will stumble then die. It also does not idle like it should when out of the water on ear-muffs. (sounds like a miss? Sometimes if I just let it idle out of gear (on ear muffs) it will idle for a bit (15 seconds?) then will stall. But it is intermittent!

Parts recently replaced:
Fuel pump (with a fancy new marine one with the 3rd barb)
Rebuilt the original Rochester Carb (which looked brand new inside) cleaned out the in-carb filter. Set back to factory specs.
New Cap + Wires + Spark plugs (all from legit marine store)
Bought 'Hot Spark' ignition module and coil. Ended up taking the drop in out and going back to points (verified 12 volts on the coil, and still wouldn't run worth a dang, sounded like it was running on one cylinder! Figured I got a bum drop in, or the wrong magnets)
Verified timing at 6' BTDC

Warm compression test showed all cylinders between 115 and 120psi. When I pulled the plugs they all looked decent (light brown on the center insulator, proper gap etc)

Also noted: right as it is stalling i hear the carb sucking air (like when you slam it WOT) but the throttle is closed.

Thanks in advance! This forum has saved me so many times!

What should I check next? Valves?

 

[jamnajar]

Re: Mercury 165 Idle issues

your intermittent switch is not in the right position I had the exact same problem up untill today take the cowl off look at how the shifter operates and make sure the switch goes in the right positions or replace it if its not in the right position it will lead you to believe you have carb problems fuel pump problems and so on

I will got isolate the interrupter switch and test today. THanks!