No low idle on Force 40

[The Mutt]

We purchased our boat with a 1997 Force 40 attached, at first the motor wouldn't start, when it did it refused to idle, I changed the plugs and filter, it now starts with the throttle on full rev but cuts out when the throttle is reduced, fuel economy rotten (2 - 2.5 hours run time) and leaves really bad oil smear on the water, I then found the carb float bowl hanging down leaking fuel before it got into the carb, explains the bad economy and fuel spill on the water.

The motor still won't idle.

I have purchased a workshop manual over the internet, it has yet to arrive and I want to get on the water, I know my way around petrol and diesel motors, not outboards, what bits do I adjust to bring the outboard back to factory settings/starting point so I can use the boat until the workshop manual arrives and I can do a proper tune-up?

No info from the previous owner about what has been adjusted on the motor.


Glenn

 

[pnwboat]

Re: No low idle on Force 40

You should probably do some basic maintenance just to eliminate any future problems.

Perform a compression check. This will tell you what kind of shape the rings/cylinders are in. Poor compression can cause a lot of problems that can have you running around in circles if not diagnosed early.

Change the lower unit oil. You should only see dark colored thick oil coming out. If any milky substance comes out, then the lower unit may have a bad seal. Water intrusion into the lower unit causes the milky effect. Could be a seal inside the lower unit, or as simple as a bad washer on the "Fill" and "Vent" plugs. Also check for glitter in the oil. Glitter is caused by small metallic particles indicating excessive wear.

Replace the water pump impeller. This requires removing the lower unit.

Replace the fuel pump diaphragm. This may be a cause for your idle problem. Or could be idle speed adjustment or idle mixture adjustment. I would caution you about adjusting the idle mixture. They call it idle mixture, but it also affects mixture at higher speeds too. If it's adjusted too lean, you can melt a piston. Typical setting is turning the adjustment screw one to one and a half turns out from lightly seated.

Replace the carburetor fuel inlet needle valve, and make sure the float is properly adjusted. Typically, the float should rest parallel to the carburetor body when holding the carburetor upside down.

Check the gas tank for debris or any other contamination.

Install an inline fuel filter (if it doesn't have one) between the fuel pump and carburetor.

 

[The Mutt]

Re: No low idle on Force 40

You should probably do some basic maintenance just to eliminate any future problems.

Perform a compression check. This will tell you what kind of shape the rings/cylinders are in. Poor compression can cause a lot of problems that can have you running around in circles if not diagnosed early.

Will check the compression when the rain stops.

Change the lower unit oil. You should only see dark colored thick oil coming out. If any milky substance comes out, then the lower unit may have a bad seal. Water intrusion into the lower unit causes the milky effect. Could be a seal inside the lower unit, or as simple as a bad washer on the "Fill" and "Vent" plugs. Also check for glitter in the oil. Glitter is caused by small metallic particles indicating excessive wear.


Replace the water pump impeller. This requires removing the lower unit.

Already done the lower leg and impeller, the oil was in good shape with no foreign objects, etc.

Replace the fuel pump diaphragm. This may be a cause for your idle problem. Or could be idle speed adjustment or idle mixture adjustment. I would caution you about adjusting the idle mixture. They call it idle mixture, but it also affects mixture at higher speeds too. If it's adjusted too lean, you can melt a piston. Typical setting is turning the adjustment screw one to one and a half turns out from lightly seated.

Had the mixture 1 turn, 2 turns, 3 turns, etc, same result, only goes at full throttle!

Replace the carburetor fuel inlet needle valve, and make sure the float is properly adjusted. Typically, the float should rest parallel to the carburetor body when holding the carburetor upside down.

Float rests flat when carb upside down, will get a new needle valve.

Check the gas tank for debris or any other contamination.

Am using new fuel in a cleaned out tank, all good here.

Install an inline fuel filter (if it doesn't have one) between the fuel pump and carburetor.

Already changed the filter, the old one was in good shape but I changed it to know the exact condition it was in.

Thanks for the help pnwboat.


Glenn

 

[pnwboat]

Re: No low idle on Force 40

Looks like you've covered most of the basic steps. When the weather clears, check the compression and change that fuel pump diaphragm.

 

[The Mutt]

Re: No low idle on Force 40

Compression test done, 150 psi on both cylinders, same reading multiple times, still got 150 psi with a bit of light oil added to the cylinders before cranking.

Don't know if that within specs, I'm use to small truck diesel engines, glad I still had a petrol engine compression tester from when I had to test V8 motors.

If we can get to our boat parts guy Tomorrow I'll be ordering the parts.

Glenn

 

[pnwboat]

Re: No low idle on Force 40

150 PSI (pounds per square inch), would indicate that the rings and cylinders are in very good shape, however, the addition of light oil has a tendency to increase the reading as opposed to testing "dry" without oil. Typical readings without oil are somewhere in the 120 PSI range. Regardless, both cylinders are equal and probably reading towards the high end which means you have a good seal between the rings and cylinders.

 

[The Mutt]

Re: No low idle on Force 40

Finally got the pump diaphragm kit and needle inlet installed, (Christmas and New Years got in the way) the motor is now a bit easier to start but still won't slow idle.

I turned the screw on to of the carb all the way in, backed off 1 1/2 turns, started the motor, the motor roars, I tried turning the screw 1/4 turn, 1/4 turn, etc in both directions, expecting to hear the the revs increase/decrease ... nothing.

The plugs are clean, the fuel line and bulb are new ............. What am I missing.

Glenn

 

[pnwboat]

Re: No low idle on Force 40

When you say the motors "roars" I am assuming it is revving very high? Try adjusting the idle speed screw. Someone may have cranked it all the way in. See item 13 in the diag. below. There is a lock nut (item 14) to keep the screw from moving. Loosen the lock nut, back the idle speed screw off a bit and see if that helps. Once you get it set, tighten the lock nut back up.

You may have to adjust the idle mixture again. Best way to adjust is on the water with a load on the motor. If it stalls right away when you go from idle to WOT, it is set too lean (turn screw out to rich). If it stumbles and hesitates then picks up, it set too rich (turn screw in to lean out). When you make your adjustments, turn the screw an 1/8 of a turn at a time and let the motor run for 15 20 seconds before testing again.

http://www.boats.net/parts/search/Merc2/Force/40%20H.P.%20%281997%29/0E203000%20THRU%200E287999/SHIFT%20AND%20THROTTLE%20LINKAGE/parts.html

 

[The Mutt]

Re: No low idle on Force 40

My "roars" comment does mean high idle, the motor is running not far from maximum revs.

I adjusted the idle screw out a full turn, that lowered the revs a little, not enough to allow a proper idle, I then would the screw out another full turn which gave a little better idle but not much, the reason there was so little improvement the second time was that the screw was no longer in contact with the motor, is there any other adjuster that I can alter?

Altering the mixture screw did nothing.

I have also sprayed some WD40 around the Carb/motor gasket to see if there was an air leak, the motor didn't alter at all.


Glenn

 

[pnwboat]

Re: No low idle on Force 40

If the throttle plate is open, the idle circuit is basically by-passed. That may be why adjusting the idle mixture screws has little affect.

With the motor shut off and the throttle in the idle position, look into the mouth of the carburetor. The throttle plate should be completely closed. Actually there should be a very very tiny gap, but for all intense purposes for this discussion we'll call it completely closed. If it is still open, then there must be something mis-adjusted in the linkage between the tower shaft (the vertical shaft assy. that the idle screw is attached to) and the carbs. Look at items 7,8,and 9 in the diagram below. The 2 plastic snap fittings (7) are threaded onto the rod (9) and are held in place by lock-nuts(8). If the plastic fittings are adjusted too far away from each other, it will essentially make the whole rod assy. longer, thus opening the throttle plate more. I'm not sure if they can be adjusted too far out to cause the motor to rev that high though. Also look at the throttle cam (item 4). The roller from the carburetor throttle shaft should be resting at the very bottom portion of the throttle cam at idle.

http://www.boats.net/parts/search/Merc2/Force/40%20H.P.%20%281997%29/0E203000%20THRU%200E287999/SHIFT%20AND%20THROTTLE%20LINKAGE/parts.html

Check that out and let us know what you find.

 

[The Mutt]

Re: No low idle on Force 40

The throttle plate is closed, I removed the throttle cam to confirm there was no more movement, the line on the lower edge of the throttle cam lines up with the throttle shaft roller.

As the throttle plate closed up I left the link and plastic snap parts alone.

Glenn

p.s. strange, I would have sworn that the post I made here this Afternoon went through Ok .. oh well.

 

[pnwboat]

Re: No low idle on Force 40

OK so that confirms that the throttle plate is closed and operating correctly. It almost sounds like there is something wrong with the fuel/air mixture. Possibly running too lean. There's only a couple of things that can cause that. A vacuum leak, or I would suspect that there is something wrong with the carburetor, or possibly a problem with the reed valves.

Make sure all of the vacuum hoses are attached and in good working order. No cracks leaks etc.

Double check the carburetor. Used some carburetor cleaner in the aerosol can to clean out all of the passages, especially in the idle circuit. Pay particular attention to the passages and the intermediate jet (item 2) and associated passages. See the diagram below. There may be a screw that covers the intermediate jet.

http://www.boats.net/parts/search/Merc2/Force/40%20H.P.%20%281997%29/0E203000%20THRU%200E287999/CARBURETOR%20-%2040%20H.P./parts.html

If all is well with the carb, then move on to the reed valve assy. If any of the reed valve petals are bent,broken or cracked, you'll have performance problems. To gain access to the reed valve assy, you will have to remove the carburetor and carburetor adapter. There are two gaskets. Use caution to avoid tearing them. Reed valves act as one way valves for the fuel/air mixture flowing into the crankcase and into the combustion chamber. Very important part of the induction system for the motor.

http://www.boats.net/parts/search/Merc2/Force/40%20H.P.%20%281997%29/0E203000%20THRU%200E287999/REED%20PLATE%20AND%20ADAPTER%20FLANGE/parts.html

 

[john from md]

Re: No low idle on Force 40

Have you checked your timing? Advanced timing will cause an engine to run at higher rpm. Also, if you have a vacuum leak at the carb, the engine will tend to run fast.

John

 

[The Mutt]

Re: No low idle on Force 40

I cleaned the Carb passages, still no change, heavy rain brought a halt to pulling apart the reed valve assembly, with any luck I'll be able to get back too it this weekend.

The vacuum hose are in good shape.

If it was a V8 car motor I could adjust the timing, on a 2 stroke where do I start, which part is the alternator, do outboards have points?

An old timer mechanic once showed me that by spaying some WD40 (Water Displacement Spray) around the base of the carb, if there is an air leak the motor will alter in revs temporarily, I have used this technique before and it does work, alas no change to the revs of my outboard.

Glenn

 

[john from md]

Re: No low idle on Force 40

Glenn,

You don't have any points to worry about as your engine uses a Capacitive Discharge Ignition system (CDI). The Alternator is not like you are used to in an auto or truck. It is a set of coils under the flywheel that works in conjunction with the permanent magnets glued to the flywheel.

Timing is controlled by rotating another coil called a trigger which is also under the flywheel. The timing is mechanical in that when you advance the power lever, you are opening the throttle and advancing the timing at the same time via a link from the throttle cable to the trigger. When you get your manual, you can read all about this.

On another note, later Force/Mercury engines used an enrichment solinoid for choking the engine rather than traditional choke plates. If your engine has the solinoid, and it is stuck open, that may be why it is revving so high.

Just a guess.

John

 

[The Mutt]

Re: No low idle on Force 40

I might leave the CDI system till after checking out the Reed Valve Assembly, the engine solenoid, is that item 39.

http://www.boats.net/parts/search/M...IGNITION AND ELECTRICAL COMPONENTS/parts.html

I normally test solenoids by removing all wires going to the solenoid, doing an Ohms test across the contact terminals - replace if reading is anything other than zero, connect 12 volts to the coil contacts, the Ohm meter should read continuity.

Is there a better way of testing the solenoids health?


Glenn

 

[pnwboat]

Re: No low idle on Force 40

I believe John is referring to the "fuel enrichment solenoid", item 11. To see if it is leaking, just disconnect the small line that goes from the solenoid to the mounting base of the carburetor or to the intake manifold. Not sure where it goes on you particular motor. There should be no gas coming out of the line until you engage the choke.

Don't disconnect the line between the fuel bowl and the solenoid or you will drain all the gas out of the bowl. This is the fuel supply to the solenoid.

http://www.boats.net/parts/search/Merc2/Force/40%20H.P.%20%281997%29/0E203000%20THRU%200E287999/RECIRCULATION%20AND%20PRIME%20SYSTEM/parts.html

 

[john from md]

Re: No low idle on Force 40

pnw is correct. Go to the recirculation and prime schematic at the same web site you were using. It is item 11 on that slide.

As he stated, if you pull off the output line, place it in a jar and activate the choke you will see if it works. It should not have any fuel coming out of it until you engage the choke.

As for the CDI's, I don't think you have any problem with them as the engine is running. CDI failure is usually lack of spark.

Let us know what you find.

John

 

[The Mutt]

Re: No low idle on Force 40

Our motor does have the "fuel enrichment solenoid", if it isn't raining I'll check the solenoid and the "Reed Valve Assembly" in the morning.

Thanks for helping me muddle through this, while I know my way around V8 motors and small truck diesel motors, 2 stroke outboards are a beast in their own right, being able to discuss what to do instead of going though a service manual trying to decide which bit to to work on next helps heaps, thanks again.

Glenn

 

[The Mutt]

Re: No low idle on Force 40

Is this the source of all my problems?

I was removing the Carb from the motor to get to the Enrichment solenoid hose connection on the bottom of the Carb housing, the Carb float was still had fuel in it, when the Carb was turn on it's side to remove the hose fuel poured (not a slight dribble) from the hole on the left side of the Carb

Is this correct?

I'll continue to checking the Enrichment solenoid and the Reed Valve Assembly.

Glenn