outboard hard to idle at dock?

[tavacska]

It happened many times, especially when I tried to retrieve the boat at dock.
Engine is 1977 1150 inline 6 mercury, boat is a 1977 boston whaler Newport.

When in open water area, the engine idles forward and back very good, sometimes a little bit choke, most time no problem. It could only dies when I lower the speed to idle in a sudden.

But when I park the boat at dock, get my truck ready, it's very hard to put it in idle gear position. Whenever I put it to gear, it chokes and dies. It already caused 3 scratches on my boat because of the problem.

My guess is the water in docking area put more resistance and load to propeller, the same as when I lower the speed in a sudden in open water. And my idle speed is too low in that case.

Idle speed was 900-1000 rpm idle no gear, 600-700 rpm in gear.
Now I turn it to 1200 rpm idle no gear, 700-800 rpm in gear.
Have not tried in water yet. But first want to know if anyone has the same experience.

 

[racerone]

Open low speed jets 1/4 turn.----Costs nothing to try that.

 

[Chris1956]

1200 RPM in neutral is too high. The gears will take abuse when shifting at that speed.

900-1000 RPM is the right idle speed in neutral.

If you have a cold start lever on your controls, pull it up, when you go get your truck. Put it back down before shifting.

As Racer said, your idle mixture may be off, or the carbs are dirty.

 

[tavacska]

I tried that 1/4 several times already.
Now it's already 2 1/2 - 2 3/4 turn from seat. The manual recommends 1 1/2 for start.
Will try that again for 3 full turn.

The carb can not be dirty, for sure. I cleaned it several times thoroughly just month before.

 

[racerone]

If you have already done the carburetor adjustment , then something else is wrong.---What has been done to this engine and what trouble shooting has been done ?

 

[tavacska]

If you have already done the carburetor adjustment , then something else is wrong.---What has been done to this engine and what trouble shooting has been done ?

This is a used motor and boat.
I basically replaced everything for the outboard, except for the crank 12-pole alternator.
All the oil, spark system is brand new. Carburetor cleaned thoroughly. All wiring is re-wired. Piston rings replaced too.

Only concern is I installed the restrict plug in the exhaust tiny holes, as suggested in manual. I don't know whether it helps or hurts the idle situation.

Now the motor runs good at high speed, never dare to try the full wide throttle, because it is already 40 mph with 4000 rpm. Only concern is the idle running.

1. First start always takes some time, like 10 sec. I have to wait patiently to hear the motor pickup the spark.
2. Idle neutral is good. But put in gear at dock can be a failure, (50%). But once it doesn't die, I runs ok with idle forward. In open area, it runs good, 90% success when put in idle forward.
3. When in idle neutral or in gear, the tachometer finger vibrates up and down, about 100 rpm in range. However in high speed, it looks pretty stable.
4. Never calibrate or know the accuracy of the tachometer. I have tried to compare it with another used one side by side, this tachometer now in use is 100-200 rpm lower than the other one.
5. The carburetor idle setting is tuned in water tank. Can hear no difference between 2 turn - 3 1/2 turn. I set it to 2 turn at first, find it to be too hard to start. So set it to 2 1/2 - 2 3/4, easier to start.

My concerns,

1. The tachometer vibrates up and down at idle really bother me but I have nothing to do about it. The spark gap is tested to be 3/4", switch, trigger, sparks all new. Cleaned the distributor house. But I didn't change the spark lines.
2. The RPM is not calibrated. I tried the multi-meter rpm test, still no good data available. There is some click motion when I put in gear, but seems no difference between the 1000 rpm and 1200 rpm.

 

[racerone]

Do you mean the 5 restrictors located behind the intake bypass covers ??----Those would help the idle.

 

[tavacska]

Yes, That's what I am talking about, thanks.

 

[racerone]

Have to ask----Why did you mention " exhaust tiny holes " in post # 6 ?

 

[tavacska]

Have to ask----Why did you mention " exhaust tiny holes " in post # 6 ?

My bad, I did mean the intake, not the exhaust. I never cleaned the exhaust side.

 

[DeepCMark58A]

I did not see something on the list, did you rebuild the fuel pump and replace the check valves inside the fuel pump, second question did you use genuine Mercury rebuild parts?

 

[tavacska]

I did not see something on the list, did you rebuild the fuel pump and replace the check valves inside the fuel pump, second question did you use genuine Mercury rebuild parts?

I don't remember the check valves inside the fuel pump. I did replace the plastic parts of with the OEM package. And I do a test when I crank the engine, the fuel pumped out flawlessly.

The OEM parts I replaced are: switch/coil/all the gasket/carb kit/fuel pump/water pump/piston ring
No OEM parts I replaced are: solenoids, starter, trigger, sparks

But your question about fuel reminds me of the fuel tank.

I am using Moeller 12 gallon tank with the self-blabla cap. I always have doubt on the cap, because whenever I push that button, it sucks air into tank, which means there is not a good air port for the tank. Could that be the reason that sometimes the idle dies ?

 

[tavacska]

Before taking the boat out to water, I did a tachometer calibration today.

I use the multi-meter Hz test on the Tachometer signal and ground and found out an interesting result.

For neutral gear, run RPM from 1500 to 2400 RPM, the multi-meter shows 150 Hz - 230 Hz, which is correct and means the tachometer is accurate. The formula is RPM = Hz * 60 / 6;(for 12 pole 6 cycle pulses)

However, when the RPM turn to idle around 1000 RPM, the multi-meter reads 300-400 Hz. Tried this several times, and the change line is around 1200-1300 RPM.

This is very interesting, and I can't explain this.

The multi-meter reading must be right. I tried another method testing by wrapping around #1 spark line and have the same result as 300-400 Hz for 1000 RPM.

 

[tavacska]

Updates:

Put the boat on water yesterday.
Did the following:

1. Mixture screw set to 3 full turns from seating.
2.Set idle to 1100-1200 rpm in neutral, which results in 700-750 rpm in forward gear. I know 1100-1200 is high. But the RPM in forward gear just vibrate at 700 RPM. The manual doesn't mention for 1977 1150. But for others newer, it says 600-700 in forward gear, but doesn't mention RPM in neutral. So mine is set on the upper edge.


Tests:
1. Good idle at port. No stall or choke.
2. Quick slow down from 20mph won't stall the motor.

Cons:
1. Still loud in idle, not as smooth as a car engine. But with its age, maybe that's ok?
2. Smoke in idle, a lot. I am using quicksilver oil.
3. Right on the up limit of idle speed. In neutral, it can reach 1200 sometimes. But forward always come down to 700.
4. My hope is 1200 won't hurt too much comparing to 1000 as accepted by most.

 

[garbageguy]

...

My guess is the water in docking area put more resistance and load to propeller, the same as when I lower the speed in a sudden in open water. And my idle speed is too low in that case.

...

I don't see that this has been discussed further - but unless there's a significant amount of something mixed with the water in the open vs docking area - I would doubt that this comes into play